准备

模型及映射文件

  1. package com.zze.bean;
  2.  
  3. import java.util.HashSet;
  4. import java.util.Set;
  5.  
  6. public class Class {
  7.     public Class() {
  8.     }
  9.  
  10.     public Class(Integer id, String name) {
  11.         this.id = id;
  12.         this.name = name;
  13.     }
  14.  
  15.     private Integer id;
  16.     private String name;
  17.  
  18.     private Set<Student> students = new HashSet<>();
  19.  
  20.     public Integer getId() {
  21.         return id;
  22.     }
  23.  
  24.     public void setId(Integer id) {
  25.         this.id = id;
  26.     }
  27.  
  28.     public String getName() {
  29.         return name;
  30.     }
  31.  
  32.     public void setName(String name) {
  33.         this.name = name;
  34.     }
  35.  
  36.     public Set<Student> getStudents() {
  37.         return students;
  38.     }
  39.  
  40.     public void setStudents(Set<Student> students) {
  41.         this.students = students;
  42.     }
  43.  
  44.     @Override
  45.     public String toString() {
  46.         return "Class{" +
  47.                 "id=" + id +
  48.                 ", name='" + name + '\'' +
  49.                 '}';
  50.     }
  51. }

班级模型：com.zze.bean.Class

  1. <?xml version="1.0" encoding="UTF-8" ?>
  2. <!DOCTYPE hibernate-mapping PUBLIC
  3.         "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
  4.         "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
  5.  
  6. <hibernate-mapping>
  7.     <class name="com.zze.bean.Class" table="class">
  8.         <id name="id">
  9.             <generator class="native"/>
  10.         </id>
  11.         <property name="name" length="32"/>
  12.         <set name="students" cascade="save-update">
  13.             <key column="cid"/>
  14.             <one-to-many class="com.zze.bean.Student"/>
  15.         </set>
  16.     </class>
  17. </hibernate-mapping>

班级映射：com/zze/bean/Class.hbm.xml

  1. package com.zze.bean;
  2.  
  3. import java.util.Date;
  4. import java.util.HashSet;
  5. import java.util.Set;
  6.  
  7. public class Student {
  8.     public Student() {
  9.     }
  10.  
  11.     public Student(Integer id, String name, Integer age,String gender) {
  12.         this.id = id;
  13.         this.name = name;
  14.         this.age = age;
  15.         this.gender = gender;
  16.     }
  17.  
  18.     private Integer id;
  19.     private String name;
  20.     private Integer age;
  21.     private String gender;
  22.  
  23.     private Class clazz;
  24.  
  25.     public Integer getId() {
  26.         return id;
  27.     }
  28.  
  29.     public void setId(Integer id) {
  30.         this.id = id;
  31.     }
  32.  
  33.     public String getName() {
  34.         return name;
  35.     }
  36.  
  37.     public void setName(String name) {
  38.         this.name = name;
  39.     }
  40.  
  41.     public Integer getAge() {
  42.         return age;
  43.     }
  44.  
  45.     public void setAge(Integer age) {
  46.         this.age = age;
  47.     }
  48.  
  49.     public String getGender() {
  50.         return gender;
  51.     }
  52.  
  53.     public void setGender(String gender) {
  54.         this.gender = gender;
  55.     }
  56.  
  57.     public Class getClazz() {
  58.         return clazz;
  59.     }
  60.  
  61.     public void setClazz(Class clazz) {
  62.         this.clazz = clazz;
  63.     }
  64.  
  65.     @Override
  66.     public String toString() {
  67.         return "Student{" +
  68.                 "id=" + id +
  69.                 ", name='" + name + '\'' +
  70.                 '}';
  71.     }
  72. }

学生模型：com.zze.bean.Student

  1. <?xml version="1.0" encoding="UTF-8" ?>
  2. <!DOCTYPE hibernate-mapping PUBLIC
  3.         "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
  4.         "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
  5.  
  6. <hibernate-mapping>
  7.     <class name="com.zze.bean.Student" table="student">
  8.         <id name="id">
  9.             <generator class="native"/>
  10.         </id>
  11.         <property name="name" length="32"/>
  12.         <property name="age"/>
  13.         <property name="gender"/>
  14.         <many-to-one name="clazz" column="cid" class="com.zze.bean.Class"/>
  15.     </class>
  16. </hibernate-mapping>

学生映射：com/zze/bean/Student.hbm.xml

全局配置

  1. <?xml version="1.0" encoding="UTF-8" ?>
  2. <!DOCTYPE hibernate-configuration PUBLIC
  3.         "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
  4.         "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
  5. <hibernate-configuration>
  6.     <session-factory>
  7.         <property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
  8.         <property name="hibernate.connection.url">jdbc:mysql://192.168.208.153:3306/1221</property>
  9.         <property name="hibernate.connection.username">root</property>
  10.         <property name="hibernate.connection.password">root</property>
  11.         <property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>
  12.         <property name="hibernate.show_sql">true</property>
  13.         <property name="hibernate.format_sql">true</property>
  14.         <property name="current_session_context_class">thread</property>
  15.         <property name="hibernate.hbm2ddl.auto">create</property>
  16.         <mapping resource="com/zze/bean/Class.hbm.xml"></mapping>
  17.         <mapping resource="com/zze/bean/Student.hbm.xml"></mapping>
  18.     </session-factory>
  19. </hibernate-configuration>

hibernate.cfg.xml

工具类

  1. package com.zze.util;
  2.  
  3. import org.hibernate.Session;
  4. import org.hibernate.SessionFactory;
  5. import org.hibernate.cfg.Configuration;
  6.  
  7. public class HibernateUtil {
  8.     public static final Configuration cfg;
  9.     public static final SessionFactory sf;
  10.  
  11.     static {
  12.         cfg = new Configuration().configure();
  13.         sf = cfg.buildSessionFactory();
  14.     }
  15.  
  16.     public static Session openSession() {
  17.         return sf.openSession();
  18.     }
  19.  
  20.     public static Session getCurrentSession() {
  21.         return sf.getCurrentSession();
  22.     }
  23. }

com.zze.util.HibernateUtil

初始化数据

  1. @Test
  2. public void initData(){
  3.     Session session = HibernateUtil.getCurrentSession();
  4.     Transaction transaction = session.beginTransaction();
  5.     Class clazz1 = new Class(null,"软件一班");
  6.     Class clazz2 = new Class(null,"软件二班");
  7.     Class clazz3 = new Class(null,"汽修一班");
  8.     Class clazz4 = new Class(null,"汽修二班");
  9.  
  10.     Student student1 = new Student(null, "张三", 12,"男");
  11.     Student student2 = new Student(null, "李四", 13,"女");
  12.     Student student3 = new Student(null, "王五", 14,"男");
  13.     Student student4 = new Student(null, "赵六", 15,"男");
  14.     Student student5 = new Student(null, "吴刚", 39,"男");
  15.     Student student6 = new Student(null, "王如花", 30,"女");
  16.     Student student7 = new Student(null, "李志静", 49,"女");
  17.     Student student8 = new Student(null, "何王天", 30,"男");
  18.  
  19.     clazz1.getStudents().add(student1);
  20.     clazz1.getStudents().add(student2);
  21.     clazz2.getStudents().add(student3);
  22.     clazz2.getStudents().add(student4);
  23.     clazz3.getStudents().add(student5);
  24.     clazz3.getStudents().add(student6);
  25.     clazz4.getStudents().add(student7);
  26.     clazz4.getStudents().add(student8);
  27.  
  28.     session.save(clazz1);
  29.     session.save(clazz2);
  30.     session.save(clazz3);
  31.     session.save(clazz4);
  32.     transaction.commit();
  33. }

init data

几种检索方式

OID检索

  • 简介

    Hibernate 根据对象的 OID（主键）进行检索。

  • 示例

    1. @Test
    2. public void test1(){
    3.     Session session = HibernateUtil.getCurrentSession();
    4.     Transaction transaction = session.beginTransaction();
    5.     Class clazz = session.get(Class.class, 1);
    6.     System.out.println(clazz);
    7.     transaction.commit();
    8.     /*
    9.     Hibernate:
    10.         select
    11.             class0_.id as id1_0_0_,
    12.             class0_.name as name2_0_0_
    13.         from
    14.             class class0_
    15.         where
    16.             class0_.id=?
    17.     Class{id=1, name='软件一班'}
    18.      */
    19. }

    例 1：使用 get 方法

    1. @Test
    2. public void test2() {
    3.     Session session = HibernateUtil.getCurrentSession();
    4.     Transaction transaction = session.beginTransaction();
    5.     Class clazz = session.load(Class.class, 1);
    6.     System.out.println(clazz);
    7.     transaction.commit();
    8.     /*
    9.     Hibernate:
    10.         select
    11.             class0_.id as id1_0_0_,
    12.             class0_.name as name2_0_0_
    13.         from
    14.             class class0_
    15.         where
    16.             class0_.id=?
    17.     Class{id=1, name='软件一班'}
    18.      */
    19. }

    例 2：使用 load 方法

对象导航检索

  • 简介

    Hibernate 根据一个已经查询到的对象，获得其关联的对象的一种查询方式。

  • 示例

    1. @Test
    2. public void test3(){
    3.     Session session = HibernateUtil.getCurrentSession();
    4.     Transaction transaction = session.beginTransaction();
    5.     Class clazz = session.load(Class.class, 1);
    6.     System.out.println(clazz);
    7.     System.out.println(Arrays.toString(clazz.getStudents().toArray()));
    8.     transaction.commit();
    9.     /*
    10.     Hibernate:
    11.         select
    12.             class0_.id as id1_0_0_,
    13.             class0_.name as name2_0_0_
    14.         from
    15.             class class0_
    16.         where
    17.             class0_.id=?
    18.     Class{id=1, name='软件一班'}
    19.     Hibernate:
    20.         select
    21.             students0_.cid as cid5_1_0_,
    22.             students0_.id as id1_1_0_,
    23.             students0_.id as id1_1_1_,
    24.             students0_.name as name2_1_1_,
    25.             students0_.age as age3_1_1_,
    26.             students0_.gender as gender4_1_1_,
    27.             students0_.cid as cid5_1_1_
    28.         from
    29.             student students0_
    30.         where
    31.             students0_.cid=?
    32.     [Student{id=2, name='张三'}, Student{id=1, name='李四'}]
    33.      */
    34. }

    例 3：

HQL检索

  • 简介

    Hibernate Language Query，Hibernate 本身提供语法支持的一种检索方式。

  • 示例

    1. /**
    2.  * 查询所有班级
    3.  */
    4. @Test
    5. public void test4(){
    6.     Session session = HibernateUtil.getCurrentSession();
    7.     Transaction transaction = session.beginTransaction();
    8.     String hql  ="from Class";
    9.     Query query = session.createQuery(hql);
    10.     List<Class> list = query.list();
    11.     System.out.println(list);
    12.     transaction.commit();
    13.     /*
    14.     Hibernate:
    15.         select
    16.             class0_.id as id1_0_,
    17.             class0_.name as name2_0_
    18.         from
    19.             class class0_
    20.     [Class{id=1, name='软件一班'}, Class{id=2, name='软件二班'}, Class{id=3, name='汽修一班'}, Class{id=4, name='汽修二班'}]
    21.      */
    22. }

    例 4：简单查询

    1. @Test
    2. public void test5(){
    3.     Session session = HibernateUtil.getCurrentSession();
    4.     Transaction transaction = session.beginTransaction();
    5.     String hql  ="select c from Class c";
    6.     Query query = session.createQuery(hql);
    7.     List<Class> list = query.list();
    8.     System.out.println(list);
    9.     transaction.commit();
    10.     /*
    11.         Hibernate:
    12.             select
    13.                 class0_.id as id1_0_,
    14.                 class0_.name as name2_0_
    15.             from
    16.                 class class0_
    17.         [Class{id=1, name='软件一班'}, Class{id=2, name='软件二班'}, Class{id=3, name='汽修一班'}, Class{id=4, name='汽修二班'}]
    18.      */
    19. }

    例 5：别名查询

    1. /**
    2.  * 根据年龄排序
    3.  */
    4. @Test
    5. public void test6(){
    6.     Session session = HibernateUtil.getCurrentSession();
    7.     Transaction transaction = session.beginTransaction();
    8.     // 升序
    9.     String hql = "from Student order by age";
    10.     // 降序
    11.     // String hql = "from Student order by age desc";
    12.     Query query = session.createQuery(hql);
    13.     List<Class> list = query.list();
    14.     System.out.println(list);
    15.     transaction.commit();
    16.     /*
    17.     Hibernate:
    18.         select
    19.             student0_.id as id1_1_,
    20.             student0_.name as name2_1_,
    21.             student0_.age as age3_1_,
    22.             student0_.gender as gender4_1_,
    23.             student0_.cid as cid5_1_
    24.         from
    25.             student student0_
    26.         order by
    27.             student0_.age
    28.     [Student{id=2, name='张三'}, Student{id=1, name='李四'}, Student{id=3, name='王五'}, Student{id=4, name='赵六'}, Student{id=6, name='王如花'}, Student{id=8, name='何王天'}, Student{id=5, name='吴刚'}, Student{id=7, name='李志静'}]
    29.      */
    30. }

    例 6：排序查询

    1. /**
    2.  * 一个条件，查询 name='张三' 的 Student
    3.  * 参数按位置绑定
    4.  */
    5. @Test
    6. public void test7() {
    7.     Session session = HibernateUtil.getCurrentSession();
    8.     Transaction transaction = session.beginTransaction();
    9.     String hql = "from Student where name = ?";
    10.     Query query = session.createQuery(hql);
    11.     query.setParameter(0, "张三");
    12.     List<Student> list = query.list();
    13.     System.out.println(list);
    14.     transaction.commit();
    15.     /*
    16.     Hibernate:
    17.         select
    18.             student0_.id as id1_1_,
    19.             student0_.name as name2_1_,
    20.             student0_.age as age3_1_,
    21.             student0_.gender as gender4_1_,
    22.             student0_.cid as cid5_1_
    23.         from
    24.             student student0_
    25.         where
    26.             student0_.name=?
    27.     [Student{id=2, name='张三'}]
    28.      */
    29. }
    30.  
    31. /**
    32.  * 多个条件 查询 name 中包含 '王' 且 age 大于 18 的Student
    33.  * 参数按名称绑定
    34.  */
    35. @Test
    36. public void test8() {
    37.     Session session = HibernateUtil.getCurrentSession();
    38.     Transaction transaction = session.beginTransaction();
    39.     String hql = "from Student where name like :name and age>:age";
    40.     Query query = session.createQuery(hql);
    41.     query.setParameter("name", "%王%");
    42.     query.setParameter("age", 18);
    43.     List<Student> list = query.list();
    44.     System.out.println(list);
    45.     transaction.commit();
    46.     /*
    47.     Hibernate:
    48.         select
    49.             student0_.id as id1_1_,
    50.             student0_.name as name2_1_,
    51.             student0_.age as age3_1_,
    52.             student0_.gender as gender4_1_,
    53.             student0_.cid as cid5_1_
    54.         from
    55.             student student0_
    56.         where
    57.             (
    58.                 student0_.name like ?
    59.             )
    60.             and student0_.age>?
    61.     [Student{id=6, name='王如花'}, Student{id=8, name='何王天'}]
    62.      */
    63. }

    例 7：条件查询

    1. /**
    2.  * 查询单个属性 返回 Object List
    3.  */
    4. @Test
    5. public void test9() {
    6.     Session session = HibernateUtil.getCurrentSession();
    7.     Transaction transaction = session.beginTransaction();
    8.     String hql = "select s.name from Student s";
    9.     Query query = session.createQuery(hql);
    10.     List<Object> list = query.list();
    11.     System.out.println(list);
    12.     transaction.commit();
    13. /*
    14. Hibernate:
    15.     select
    16.         student0_.name as col_0_0_
    17.     from
    18.         student student0_
    19. [李四, 张三, 王五, 赵六, 吴刚, 王如花, 李志静, 何王天]
    20.  */
    21. }
    22.  
    23. /**
    24.  * 查询多个属性 返回 Object[] List
    25.  */
    26. @Test
    27. public void test10() {
    28.     Session session = HibernateUtil.getCurrentSession();
    29.     Transaction transaction = session.beginTransaction();
    30.     String hql = "select s.name,s.age from Student s";
    31.     Query query = session.createQuery(hql);
    32.     List<Object[]> list = query.list();
    33.     for (Object[] objects : list) {
    34.         System.out.println(Arrays.toString(objects));
    35.     }
    36.     transaction.commit();
    37.     /*
    38.     Hibernate:
    39.         select
    40.             student0_.name as col_0_0_,
    41.             student0_.age as col_1_0_
    42.         from
    43.             student student0_
    44.     [李四, 13]
    45.     [张三, 12]
    46.     [王五, 14]
    47.     [赵六, 15]
    48.     [吴刚, 39]
    49.     [王如花, 30]
    50.     [李志静, 49]
    51.     [何王天, 30]
    52.      */
    53. }
    54.  
    55. /**
    56.  * 查询多个属性 返回对应对象类型 List
    57.  */
    58. @Test
    59. public void test11() {
    60.     Session session = HibernateUtil.getCurrentSession();
    61.     Transaction transaction = session.beginTransaction();
    62.     /*
    63.     需要让模型提供对应构造：
    64.         public Student(String name, Integer age) {
    65.             this.name = name;
    66.             this.age = age;
    67.         }
    68.      */
    69.     String hql = "select new Student(name,age) from Student";
    70.     Query query = session.createQuery(hql);
    71.     List<Student> list = query.list();
    72.     System.out.println(list);
    73.     transaction.commit();
    74.     /*
    75.     Hibernate:
    76.         select
    77.             student0_.name as col_0_0_,
    78.             student0_.age as col_1_0_
    79.         from
    80.             student student0_
    81.     [Student{id=null, name='李四'}, Student{id=null, name='张三'}, Student{id=null, name='王五'}, Student{id=null, name='赵六'}, Student{id=null, name='吴刚'}, Student{id=null, name='王如花'}, Student{id=null, name='李志静'}, Student{id=null, name='何王天'}]
    82.      */
    83. }

    例 8：投影查询

    1. @Test
    2. public void test12() {
    3.     Session session = HibernateUtil.getCurrentSession();
    4.     Transaction transaction = session.beginTransaction();
    5.     String hql = "from Student";
    6.     Query query = session.createQuery(hql);
    7.     query.setFirstResult(0); // 起始行索引
    8.     query.setMaxResults(3); // 每页条数
    9.     List<Student> list = query.list();
    10.     System.out.println(list);
    11.     transaction.commit();
    12.     /*
    13.     Hibernate:
    14.         select
    15.             student0_.id as id1_1_,
    16.             student0_.name as name2_1_,
    17.             student0_.age as age3_1_,
    18.             student0_.gender as gender4_1_,
    19.             student0_.cid as cid5_1_
    20.         from
    21.             student student0_ limit ?
    22.     [Student{id=1, name='李四'}, Student{id=2, name='张三'}, Student{id=3, name='王五'}]
    23.  
    24.     Process finished with exit code 0
    25.      */
    26. }

    例 9：分页查询

    1. /**
    2.  * 聚合查询
    3.  */
    4. @Test
    5. public void test13() {
    6.     Session session = HibernateUtil.getCurrentSession();
    7.     Transaction transaction = session.beginTransaction();
    8.     // 聚合函数使用 count max min avg sum
    9.     String hql = "select count(1) from Student";
    10.     Query query = session.createQuery(hql);
    11.     Object o = query.uniqueResult();
    12.     System.out.println(o.getClass());
    13.     System.out.println(o);
    14.     transaction.commit();
    15.     /*
    16.     Hibernate:
    17.         select
    18.             count(1) as col_0_0_
    19.         from
    20.             student student0_
    21.     class java.lang.Long
    22.     8
    23.      */
    24. }
    25.  
    26. /**
    27.  * 分组查询 返回 Object[] List
    28.  * 根据 gender 分组，查询每个 gender 的对应数据条数
    29.  */
    30. @Test
    31. public void test14() {
    32.     Session session = HibernateUtil.getCurrentSession();
    33.     Transaction transaction = session.beginTransaction();
    34.     String hql = "select gender,count(1) from Student group by gender";
    35.     Query query = session.createQuery(hql);
    36.     List<Object[]> list = query.list();
    37.     for (Object[] objects : list) {
    38.         System.out.println(Arrays.toString(objects));
    39.     }
    40.     transaction.commit();
    41.     /*
    42.     Hibernate:
    43.         select
    44.             student0_.gender as col_0_0_,
    45.             count(1) as col_1_0_
    46.         from
    47.             student student0_
    48.         group by
    49.             student0_.gender
    50.     [女, 3]
    51.     [男, 5]
    52.      */
    53. }

    例 10：聚合及分组统计查询

    1. @Test
    2. public void test23() {
    3.     Session session = HibernateUtil.getCurrentSession();
    4.     Transaction transaction = session.beginTransaction();
    5.     String hql = "from Student c join c.clazz";
    6.     Query query = session.createQuery(hql);
    7.     List<Object[]> list = query.list();
    8.     for (Object[] objects : list) {
    9.         System.out.println(Arrays.toString(objects));
    10.     }
    11.     transaction.commit();
    12.     /*
    13.     Hibernate:
    14.         select
    15.             student0_.id as id1_1_0_,
    16.             class1_.id as id1_0_1_,
    17.             student0_.name as name2_1_0_,
    18.             student0_.age as age3_1_0_,
    19.             student0_.gender as gender4_1_0_,
    20.             student0_.cid as cid5_1_0_,
    21.             class1_.name as name2_0_1_
    22.         from
    23.             student student0_
    24.         inner join
    25.             class class1_
    26.                 on student0_.cid=class1_.id
    27.     [Student{id=1, name='李四'}, Class{id=1, name='软件一班'}]
    28.     [Student{id=2, name='张三'}, Class{id=1, name='软件一班'}]
    29.     [Student{id=3, name='王五'}, Class{id=2, name='软件二班'}]
    30.     [Student{id=4, name='赵六'}, Class{id=2, name='软件二班'}]
    31.     [Student{id=5, name='吴刚'}, Class{id=3, name='汽修一班'}]
    32.     [Student{id=6, name='王如花'}, Class{id=3, name='汽修一班'}]
    33.     [Student{id=7, name='李志静'}, Class{id=4, name='汽修二班'}]
    34.     [Student{id=8, name='何王天'}, Class{id=4, name='汽修二班'}]
    35.      */
    36. }

    例 11：普通内连接

    1. /**
    2.  * 查询所有学生及其班级
    3.  */
    4. @Test
    5. public void test24() {
    6.     /*
    7.     迫切内连接
    8.     其实就是在普通的内连接 inner join 后添加关键字 fetch
    9.     将关联表数据封装到查询对象的属性中
    10.      */
    11.     Session session = HibernateUtil.getCurrentSession();
    12.     Transaction transaction = session.beginTransaction();
    13.     String hql = "from Student c join fetch c.clazz";
    14.     Query query = session.createQuery(hql);
    15.     List<Student> list = query.list();
    16.     for (Student student : list) {
    17.         System.out.println(String.format("%s %s", student, student.getClazz()));
    18.     }
    19.     transaction.commit();
    20.     /*
    21.     Hibernate:
    22.         select
    23.             student0_.id as id1_1_0_,
    24.             class1_.id as id1_0_1_,
    25.             student0_.name as name2_1_0_,
    26.             student0_.age as age3_1_0_,
    27.             student0_.gender as gender4_1_0_,
    28.             student0_.cid as cid5_1_0_,
    29.             class1_.name as name2_0_1_
    30.         from
    31.             student student0_
    32.         inner join
    33.             class class1_
    34.                 on student0_.cid=class1_.id
    35.     Student{id=1, name='李四'} Class{id=1, name='软件一班'}
    36.     Student{id=2, name='张三'} Class{id=1, name='软件一班'}
    37.     Student{id=3, name='王五'} Class{id=2, name='软件二班'}
    38.     Student{id=4, name='赵六'} Class{id=2, name='软件二班'}
    39.     Student{id=5, name='吴刚'} Class{id=3, name='汽修一班'}
    40.     Student{id=6, name='王如花'} Class{id=3, name='汽修一班'}
    41.     Student{id=7, name='李志静'} Class{id=4, name='汽修二班'}
    42.     Student{id=8, name='何王天'} Class{id=4, name='汽修二班'}
    43.      */
    44. }
    45.  
    46. /**
    47.  * 查询所有班级及属于该班级的学生
    48.  */
    49. @Test
    50. public void test25() {
    51.     Session session = HibernateUtil.getCurrentSession();
    52.     Transaction transaction = session.beginTransaction();
    53.     String hql = "select distinct c from Class c join fetch c.students";
    54.     Query query = session.createQuery(hql);
    55.     List<Class> list = query.list();
    56.     for (Class clazz : list) {
    57.         System.out.println(String.format("%s %s", clazz, clazz.getStudents()));
    58.     }
    59.     transaction.commit();
    60.     /*
    61.     Class{id=1, name='软件一班'} [Student{id=2, name='张三'}, Student{id=1, name='李四'}]
    62.     Class{id=2, name='软件二班'} [Student{id=4, name='赵六'}, Student{id=3, name='王五'}]
    63.     Class{id=3, name='汽修一班'} [Student{id=5, name='吴刚'}, Student{id=6, name='王如花'}]
    64.     Class{id=4, name='汽修二班'} [Student{id=7, name='李志静'}, Student{id=8, name='何王天'}]
    65.      */
    66. }

    例 12：迫切内连接

QBC检索

  • 简介

    Query By Criteria，条件查询，是一种更加面向对象化的查询方式。

  • 示例

    1. @Test
    2. public void test15(){
    3.     Session session = HibernateUtil.getCurrentSession();
    4.     Transaction transaction = session.beginTransaction();
    5.     Criteria criteria = session.createCriteria(Class.class);
    6.     List<Class> list = criteria.list();
    7.     System.out.println(list);
    8.     transaction.commit();
    9.     /*
    10.     Hibernate:
    11.         select
    12.             this_.id as id1_0_0_,
    13.             this_.name as name2_0_0_
    14.         from
    15.             class this_
    16.     [Class{id=1, name='软件一班'}, Class{id=2, name='软件二班'}, Class{id=3, name='汽修一班'}, Class{id=4, name='汽修二班'}]
    17.      */
    18. }

    例 13：简单查询

    1. @Test
    2. public void test16(){
    3.     Session session = HibernateUtil.getCurrentSession();
    4.     Transaction transaction = session.beginTransaction();
    5.     Criteria criteria = session.createCriteria(Class.class);
    6.     // 升序
    7.     criteria.addOrder(Order.asc("id"));
    8.     // 降序
    9.     // criteria.addOrder(Order.desc("id"));
    10.     List<Class> list = criteria.list();
    11.     System.out.println(list);
    12.     transaction.commit();
    13.     /*
    14.     Hibernate:
    15.         select
    16.             this_.id as id1_0_0_,
    17.             this_.name as name2_0_0_
    18.         from
    19.             class this_
    20.         order by
    21.             this_.id asc
    22.     [Class{id=1, name='软件一班'}, Class{id=2, name='软件二班'}, Class{id=3, name='汽修一班'}, Class{id=4, name='汽修二班'}]
    23.      */
    24. }

    例 14：排序查询

    1. @Test
    2. public void test17() {
    3.     Session session = HibernateUtil.getCurrentSession();
    4.     Transaction transaction = session.beginTransaction();
    5.     Criteria criteria = session.createCriteria(Student.class);
    6.     criteria.setFirstResult(0); // 数据起始索引
    7.     criteria.setMaxResults(2); // 每页数据条数
    8.     List<Student> list = criteria.list();
    9.     System.out.println(list);
    10.     transaction.commit();
    11.     /*
    12.     Hibernate:
    13.         select
    14.             this_.id as id1_1_0_,
    15.             this_.name as name2_1_0_,
    16.             this_.age as age3_1_0_,
    17.             this_.gender as gender4_1_0_,
    18.             this_.cid as cid5_1_0_
    19.         from
    20.             student this_ limit ?
    21.     [Student{id=1, name='李四'}, Student{id=2, name='张三'}]
    22.      */
    23. }

    例 15：分页查询

    1. /**
    2.  * 简单 and 条件查询
    3.  * 查询 name 包含 '王' 且 age>10
    4.  */
    5. @Test
    6. public void test18() {
    7.     Session session = HibernateUtil.getCurrentSession();
    8.     Transaction transaction = session.beginTransaction();
    9.     Criteria criteria = session.createCriteria(Student.class);
    10.     // 默认多个 criteria.add 的条件是用 and 连接
    11.     criteria.add(Restrictions.like("name", "%王%"));
    12.     criteria.add(Restrictions.gt("age", 10));
    13.     List<Student> list = criteria.list();
    14.     System.out.println(list);
    15.     transaction.commit();
    16.     /*
    17.     Hibernate:
    18.         select
    19.             this_.id as id1_1_0_,
    20.             this_.name as name2_1_0_,
    21.             this_.age as age3_1_0_,
    22.             this_.gender as gender4_1_0_,
    23.             this_.cid as cid5_1_0_
    24.         from
    25.             student this_
    26.         where
    27.             this_.name like ?
    28.             and this_.age>?
    29.     [Student{id=3, name='王五'}, Student{id=6, name='王如花'}, Student{id=8, name='何王天'}]
    30.      */
    31. }
    32.  
    33. /**
    34.  * 简单 or 条件查询
    35.  * 查询 name 包含 '王' 或 name 包含 '张'
    36.  */
    37. @Test
    38. public void test19() {
    39.     Session session = HibernateUtil.getCurrentSession();
    40.     Transaction transaction = session.beginTransaction();
    41.     Criteria criteria = session.createCriteria(Student.class);
    42.     // or 条件可以通过 Restrictions.or 方法实现
    43.     criteria.add(Restrictions.or(Restrictions.like("name", "%王%"), Restrictions.like("name", "%张%")));
    44.     List<Student> list = criteria.list();
    45.     System.out.println(list);
    46.     transaction.commit();
    47.  
    48.     /*
    49.     Hibernate:
    50.         select
    51.             this_.id as id1_1_0_,
    52.             this_.name as name2_1_0_,
    53.             this_.age as age3_1_0_,
    54.             this_.gender as gender4_1_0_,
    55.             this_.cid as cid5_1_0_
    56.         from
    57.             student this_
    58.         where
    59.             (
    60.                 this_.name like ?
    61.                 or this_.name like ?
    62.             )
    63.     [Student{id=2, name='张三'}, Student{id=3, name='王五'}, Student{id=6, name='王如花'}, Student{id=8, name='何王天'}]
    64.      */
    65. }
    66.  
    67. /**
    68.  * 复杂 and 和 or 查询
    69.  * 查询 (name 包含 '王' 且 age>10) 或 name 包含 '张'
    70.  */
    71. @Test
    72. public void test20() {
    73.     Session session = HibernateUtil.getCurrentSession();
    74.     Transaction transaction = session.beginTransaction();
    75.     Criteria criteria = session.createCriteria(Student.class);
    76.     // 通过 conjunction.add 添加的条件是 and 连接
    77.     Conjunction conjunction = Restrictions.conjunction();
    78.     conjunction.add(Restrictions.like("name", "%王%"));
    79.     conjunction.add(Restrictions.gt("age", 10));
    80.     // 通过 disjunction.add 添加的条件是 or 连接
    81.     Disjunction disjunction = Restrictions.disjunction();
    82.     disjunction.add(conjunction);
    83.     disjunction.add(Restrictions.like("name", "%张%"));
    84.     criteria.add(disjunction);
    85.     List<Student> list = criteria.list();
    86.     System.out.println(list);
    87.     transaction.commit();
    88.     /*
    89.     Hibernate:
    90.         select
    91.             this_.id as id1_1_0_,
    92.             this_.name as name2_1_0_,
    93.             this_.age as age3_1_0_,
    94.             this_.gender as gender4_1_0_,
    95.             this_.cid as cid5_1_0_
    96.         from
    97.             student this_
    98.         where
    99.             (
    100.                 (
    101.                     this_.name like ?
    102.                     and this_.age>?
    103.                 )
    104.                 or this_.name like ?
    105.             )
    106.     [Student{id=2, name='张三'}, Student{id=3, name='王五'}, Student{id=6, name='王如花'}, Student{id=8, name='何王天'}]
    107.      */
    108. }

    例 16：条件查询

    1. /**
    2.  * 聚合统计查询
    3.  * 统计男女人数及最大年龄
    4.  */
    5. @Test
    6. public void test21() {
    7.     Session session = HibernateUtil.getCurrentSession();
    8.     Transaction transaction = session.beginTransaction();
    9.     Criteria criteria = session.createCriteria(Student.class);
    10.     /*
    11.     criteria :
    12.         add : 普通条件，where
    13.         addOrder : 排序
    14.         setProjection : 聚合函数和 group by having
    15.      */
    16.     ProjectionList projectionList = Projections.projectionList();
    17.     projectionList.add(Projections.groupProperty("gender"));
    18.     projectionList.add(Projections.rowCount());
    19.     projectionList.add(Projections.max("age"));
    20.     criteria.setProjection(projectionList);
    21.  
    22.     List<Object[]> list = criteria.list();
    23.     for (Object[] objects : list) {
    24.         System.out.println(Arrays.toString(objects));
    25.     }
    26.     transaction.commit();
    27.     /*
    28.     Hibernate:
    29.         select
    30.             this_.gender as y0_,
    31.             count(*) as y1_,
    32.             max(this_.age) as y2_
    33.         from
    34.             student this_
    35.         group by
    36.             this_.gender
    37.     [女, 3, 49]
    38.     [男, 5, 39]
    39.      */
    40. }

    例 17：聚合及分组统计查询

    1. /**
    2.  * 离线条件查询
    3.  * 查询 name 包含 '一'
    4.  */
    5. @Test
    6. public void test22(){
    7.     DetachedCriteria detachedCriteria = DetachedCriteria.forClass(Class.class);
    8.     detachedCriteria.add(Restrictions.like("name", "%一%"));
    9.     Session session = HibernateUtil.getCurrentSession();
    10.     Transaction transaction = session.beginTransaction();
    11.     Criteria criteria = detachedCriteria.getExecutableCriteria(session);
    12.     List<Class> list = criteria.list();
    13.     System.out.println(list);
    14.     transaction.commit();
    15.     /*
    16.     Hibernate:
    17.         select
    18.             this_.id as id1_0_0_,
    19.             this_.name as name2_0_0_
    20.         from
    21.             class this_
    22.         where
    23.             this_.name like ?
    24.     [Class{id=1, name='软件一班'}, Class{id=3, name='汽修一班'}]
    25.      */
    26. }

    例 18：离线条件查询

SQL检索

  • 简介

    Hibernate 支持的原生 SQL 查询。

  • 示例

    1. /**
    2.  * 查询所有 Class，返回 Object[] List
    3.  */
    4. @Test
    5. public void test26() {
    6.     Session session = HibernateUtil.getCurrentSession();
    7.     Transaction transaction = session.beginTransaction();
    8.     String sql = "select * from class";
    9.     SQLQuery sqlQuery = session.createSQLQuery(sql);
    10.     List<Object[]> list = sqlQuery.list();
    11.     for (Object[] objects : list) {
    12.         System.out.println(Arrays.toString(objects));
    13.     }
    14.     transaction.commit();
    15.     /*
    16.     Hibernate:
    17.         select
    18.             *
    19.         from
    20.             class
    21.     [1, 软件一班]
    22.     [2, 软件二班]
    23.     [3, 汽修一班]
    24.     [4, 汽修二班]
    25.      */
    26. }
    27.  
    28. /**
    29.  * 查询所有 Class，返回 Class List
    30.  */
    31. @Test
    32. public void test27() {
    33.     Session session = HibernateUtil.getCurrentSession();
    34.     Transaction transaction = session.beginTransaction();
    35.     String sql = "select * from class";
    36.     SQLQuery sqlQuery = session.createSQLQuery(sql);
    37.     sqlQuery.addEntity(Class.class);
    38.     List<Class> list = sqlQuery.list();
    39.     for (Class clazz : list) {
    40.         System.out.println(clazz);
    41.     }
    42.     transaction.commit();
    43.     /*
    44.     Hibernate:
    45.         select
    46.             *
    47.         from
    48.             class
    49.     Class{id=1, name='软件一班'}
    50.     Class{id=2, name='软件二班'}
    51.     Class{id=3, name='汽修一班'}
    52.     Class{id=4, name='汽修二班'}
    53.      */
    54. }

    例 19：原生 SQL 查询

延迟加载

概述

只有真正使用对象的属性时才会发送 SQL 进行查询。如： session.load(Student.class,1); 。

分类

  • 类级别的延迟加载

    指的是查询某个类的对象时，针对这个类的对象是否使用延迟加载。

    除了修改 lazy="false" 这种方式，还可通过如下两种方式让 lazy 失效：

    1、将持久化类以 final 修饰。

    2、通过调用 Hibernate.initialize(proxy); 。

  • 关联级别的延迟加载

    指的是查询到某个对象后，再查询其关联的对象是否使用延迟加载。

示例

  1. /**
  2.  * 懒加载
  3.  * 修改映射文件 ：
  4.  * com/zze/bean/Class.hbm.xml :
  5.  * <class name="com.zze.bean.Class" table="class" lazy="true">
  6.  * lazy 默认为 true
  7.  */
  8. @Test
  9. public void test27() {
  10.     Session session = HibernateUtil.getCurrentSession();
  11.     Transaction transaction = session.beginTransaction();
  12.     Class clazz = session.load(Class.class, 1);
  13.     System.out.println(clazz.getClass()); // class com.zze.bean.Class_$$_jvst718_0
  14.     System.out.println(clazz); // 发出 SQL
  15.     transaction.commit();
  16. }
  17.  
  18. /**
  19.  * 立即加载
  20.  * 修改映射文件 :
  21.  * com/zze/bean/Class.hbm.xml :
  22.  * <class name="com.zze.bean.Class" table="class" lazy="false">
  23.  */
  24. @Test
  25. public void test28() {
  26.     Session session = HibernateUtil.getCurrentSession();
  27.     Transaction transaction = session.beginTransaction();
  28.     Class clazz = session.load(Class.class, 1); // 发出 SQL
  29.     System.out.println(clazz.getClass()); // class com.zze.bean.Class
  30.     System.out.println(clazz);
  31.     transaction.commit();
  32. }

例 20：类级别的延迟加载

  1. /**
  2.  * 懒加载
  3.  * 修改映射文件 ：
  4.  * com/zze/bean/Class.hbm.xml :
  5.  * <set name="students" cascade="save-update" lazy="true">
  6.  * lazy 默认为 true
  7.  */
  8. @Test
  9. public void test29() {
  10.     Session session = HibernateUtil.getCurrentSession();
  11.     Transaction transaction = session.beginTransaction();
  12.     Class clazz = session.get(Class.class, 1);
  13.     Set<Student> students = clazz.getStudents();
  14.     System.out.println(students); // 发出 SQL
  15.     transaction.commit();
  16. }
  17.  
  18. /**
  19.  * 即时加载
  20.  * 修改映射文件 ：
  21.  * com/zze/bean/Class.hbm.xml :
  22.  * <set name="students" cascade="save-update" lazy="false">
  23.  */
  24. @Test
  25. public void test30() {
  26.     Session session = HibernateUtil.getCurrentSession();
  27.     Transaction transaction = session.beginTransaction();
  28.     Class clazz = session.get(Class.class, 1);
  29.     Set<Student> students = clazz.getStudents(); // 发出 SQL
  30.     System.out.println(students);
  31.     transaction.commit();
  32. }
  33.  
  34. /**
  35.  * 懒加载
  36.  * 修改映射文件 :
  37.  * com/zze/bean/Student.hbm.xml :
  38.  * <many-to-one name="clazz" lazy="proxy" column="cid" class="com.zze.bean.Class"/>
  39.  * com/zze/bean/Class.hbm.xml :
  40.  * <class name="com.zze.bean.Class" table="class" lazy="true">
  41.  * <p>
  42.  * proxy : 默认值，表示引用关联类的加载策略。
  43.  */
  44. @Test
  45. public void test31() {
  46.     Session session = HibernateUtil.getCurrentSession();
  47.     Transaction transaction = session.beginTransaction();
  48.     Student student = session.get(Student.class, 1);
  49.     Class clazz = student.getClazz();
  50.     System.out.println(clazz); // 发出 SQL
  51.     transaction.commit();
  52. }
  53.  
  54. /**
  55.  * 即时加载
  56.  * 当关联类的 lazy="false" 时，无论当前类 many-to-one 标签上的 lazy 如何配置，都是即时加载。
  57.  * 修改映射文件 :
  58.  * com/zze/bean/Student.hbm.xml :
  59.  * * <many-to-one name="clazz" lazy="proxy" column="cid" class="com.zze.
  60.  * com/zze/bean/Class.hbm.xml :
  61.  * * <class name="com.zze.bean.Class" table="class" lazy="false">
  62.  * 或 :
  63.  * com/zze/bean/Student.hbm.xml :
  64.  * * <many-to-one name="clazz" lazy="false" column="cid" class="com.zze.bean.Class"/>
  65.  * com/zze/bean/Class.hbm.xml :
  66.  * * <class name="com.zze.bean.Class" table="class" lazy="true">
  67.  */
  68. @Test
  69. public void test32() {
  70.     Session session = HibernateUtil.getCurrentSession();
  71.     Transaction transaction = session.beginTransaction();
  72.     Student student = session.get(Student.class, 1);
  73.     Class clazz = student.getClazz(); // 发出 SQL
  74.     System.out.println(clazz);
  75.     transaction.commit();
  76. }

例 21：关联级别的延迟加载

抓取策略

概述

通过一个对象抓取关联对象需要发送 SQL ，SQL 如何发送及 SQL 的发送规则就可以通过抓取策略进行配置。

通过 <set> 或 <many-to-one> 上的 fetch 属性进行配置。

要考虑fetch 和这些标签上的 lazy 如何配置才能最大化优化发送的 SQL 语句。

set标签上的fetch和lazy

  • fetch

    抓取策略，控制 SQL 语句格式。

    在这里 fetch 有三个可选值：

    select : 默认值，发送普通 select 语句查询关联对象。

    join: 发送一条迫切左外连接查询关联对象。

    subselect : 发送子查询查询关联对象。

  • lazy

    延迟加载，控制查询关联对象时是否使用懒加载。

    在这里 lazy 有三个可选值：

    true : 默认值，查询关联对象时，使用延迟加载。

    false : 查询关联对象时，不使用延迟加载。

    extra : 及其懒惰。

  • 示例

    1. /**
    2.  * com/zze/bean/Class.hbm.xml
    3.  * 默认值：
    4.  * <set name="students" cascade="save-update" fetch="select" lazy="true">
    5.  */
    6. @Test
    7. public void test33() {
    8.     Session session = HibernateUtil.getCurrentSession();
    9.     Transaction transaction = session.beginTransaction();
    10.     Class clazz = session.get(Class.class, 1);
    11.     for (Student student : clazz.getStudents()) {
    12.         System.out.println(student);// 发送 SQL
    13.     }
    14.     transaction.commit();
    15.     /*
    16.     Hibernate:
    17.         select
    18.             class0_.id as id1_0_0_,
    19.             class0_.name as name2_0_0_
    20.         from
    21.             class class0_
    22.         where
    23.             class0_.id=?
    24.     Hibernate:
    25.         select
    26.             students0_.cid as cid5_1_0_,
    27.             students0_.id as id1_1_0_,
    28.             students0_.id as id1_1_1_,
    29.             students0_.name as name2_1_1_,
    30.             students0_.age as age3_1_1_,
    31.             students0_.gender as gender4_1_1_,
    32.             students0_.cid as cid5_1_1_
    33.         from
    34.             student students0_
    35.         where
    36.             students0_.cid=?
    37.     Student{id=2, name='张三'}
    38.     Student{id=1, name='李四'}
    39.      */
    40. }
    41.  
    42. /**
    43.  * com/zze/bean/Class.hbm.xml
    44.  *
    45.  * <set name="students" cascade="save-update" fetch="select" lazy="false">
    46.  */
    47. @Test
    48. public void test34() {
    49.     Session session = HibernateUtil.getCurrentSession();
    50.     Transaction transaction = session.beginTransaction();
    51.     Class clazz = session.get(Class.class, 1); //发送 2 条 SQL
    52.     for (Student student : clazz.getStudents()) {
    53.         System.out.println(student);
    54.     }
    55.     transaction.commit();
    56.     /*
    57.     Hibernate:
    58.         select
    59.             class0_.id as id1_0_0_,
    60.             class0_.name as name2_0_0_
    61.         from
    62.             class class0_
    63.         where
    64.             class0_.id=?
    65.     Hibernate:
    66.         select
    67.             students0_.cid as cid5_1_0_,
    68.             students0_.id as id1_1_0_,
    69.             students0_.id as id1_1_1_,
    70.             students0_.name as name2_1_1_,
    71.             students0_.age as age3_1_1_,
    72.             students0_.gender as gender4_1_1_,
    73.             students0_.cid as cid5_1_1_
    74.         from
    75.             student students0_
    76.         where
    77.             students0_.cid=?
    78.     Student{id=2, name='张三'}
    79.     Student{id=1, name='李四'}
    80.      */
    81. }
    82.  
    83. /**
    84.  * com/zze/bean/Class.hbm.xml
    85.  *
    86.  * <set name="students" cascade="save-update" fetch="select" lazy="extra">
    87.  */
    88. @Test
    89. public void test35() {
    90.     Session session = HibernateUtil.getCurrentSession();
    91.     Transaction transaction = session.beginTransaction();
    92.     Class clazz = session.get(Class.class, 1);
    93.     System.out.println(clazz.getStudents().size()); // 针对数量发送一条sql
    94.     transaction.commit();
    95.     /*
    96.     Hibernate:
    97.         select
    98.             class0_.id as id1_0_0_,
    99.             class0_.name as name2_0_0_
    100.         from
    101.             class class0_
    102.         where
    103.             class0_.id=?
    104.     Hibernate:
    105.         select
    106.             count(id)
    107.         from
    108.             student
    109.         where
    110.             cid =?
    111.      */
    112. }
    113.  
    114. /**
    115.  * com/zze/bean/Class.hbm.xml
    116.  * fetch="join" 时，lazy 失效
    117.  * <set name="students" cascade="save-update" fetch="join" lazy="true">
    118.  */
    119. public void test36() {
    120.     Session session = HibernateUtil.getCurrentSession();
    121.     Transaction transaction = session.beginTransaction();
    122.     Class clazz = session.get(Class.class, 1);// 发送 SQL
    123.     for (Student student : clazz.getStudents()) {
    124.         System.out.println(student);
    125.     }
    126.     transaction.commit();
    127.     /*
    128.     Hibernate:
    129.         select
    130.             class0_.id as id1_0_0_,
    131.             class0_.name as name2_0_0_,
    132.             students1_.cid as cid5_1_1_,
    133.             students1_.id as id1_1_1_,
    134.             students1_.id as id1_1_2_,
    135.             students1_.name as name2_1_2_,
    136.             students1_.age as age3_1_2_,
    137.             students1_.gender as gender4_1_2_,
    138.             students1_.cid as cid5_1_2_
    139.         from
    140.             class class0_
    141.         left outer join
    142.             student students1_
    143.                 on class0_.id=students1_.cid
    144.         where
    145.             class0_.id=?
    146.     Student{id=2, name='张三'}
    147.     Student{id=1, name='李四'}
    148.      */
    149. }
    150.  
    151. /**
    152.  * com/zze/bean/Class.hbm.xml
    153.  *
    154.  * <set name="students" cascade="save-update" fetch="subselect" lazy="true">
    155.  */
    156. @Test
    157. public void test37() {
    158.     Session session = HibernateUtil.getCurrentSession();
    159.     Transaction transaction = session.beginTransaction();
    160.     Query query = session.createQuery("from Class");
    161.     List<Class> list = query.list();
    162.     for (Class clazz : list) {
    163.         Set<Student> students = clazz.getStudents(); // 发送 SQL
    164.         System.out.println(students);
    165.     }
    166.     transaction.commit();
    167.     /*
    168.     Hibernate:
    169.         select
    170.             class0_.id as id1_0_,
    171.             class0_.name as name2_0_
    172.         from
    173.             class class0_
    174.     Hibernate:
    175.         select
    176.             students0_.cid as cid5_1_1_,
    177.             students0_.id as id1_1_1_,
    178.             students0_.id as id1_1_0_,
    179.             students0_.name as name2_1_0_,
    180.             students0_.age as age3_1_0_,
    181.             students0_.gender as gender4_1_0_,
    182.             students0_.cid as cid5_1_0_
    183.         from
    184.             student students0_
    185.         where
    186.             students0_.cid in (
    187.                 select
    188.                     class0_.id
    189.                 from
    190.                     class class0_
    191.             )
    192.     [Student{id=1, name='李四'}, Student{id=2, name='张三'}]
    193.     [Student{id=4, name='赵六'}, Student{id=3, name='王五'}]
    194.     [Student{id=5, name='吴刚'}, Student{id=6, name='王如花'}]
    195.     [Student{id=7, name='李志静'}, Student{id=8, name='何王天'}]
    196.      */
    197. }
    198.  
    199. /**
    200.  * com/zze/bean/Class.hbm.xml
    201.  *
    202.  * <set name="students" cascade="save-update" fetch="subselect" lazy="false">
    203.  */
    204. @Test
    205. public void test38() {
    206.     Session session = HibernateUtil.getCurrentSession();
    207.     Transaction transaction = session.beginTransaction();
    208.     Query query = session.createQuery("from Class");
    209.     List<Class> list = query.list(); // 发送 SQL
    210.     for (Class clazz : list) {
    211.         Set<Student> students = clazz.getStudents();
    212.         System.out.println(students);
    213.     }
    214.     transaction.commit();
    215.     /*
    216.     Hibernate:
    217.         select
    218.             class0_.id as id1_0_,
    219.             class0_.name as name2_0_
    220.         from
    221.             class class0_
    222.     Hibernate:
    223.         select
    224.             students0_.cid as cid5_1_1_,
    225.             students0_.id as id1_1_1_,
    226.             students0_.id as id1_1_0_,
    227.             students0_.name as name2_1_0_,
    228.             students0_.age as age3_1_0_,
    229.             students0_.gender as gender4_1_0_,
    230.             students0_.cid as cid5_1_0_
    231.         from
    232.             student students0_
    233.         where
    234.             students0_.cid in (
    235.                 select
    236.                     class0_.id
    237.                 from
    238.                     class class0_
    239.             )
    240.     [Student{id=1, name='李四'}, Student{id=2, name='张三'}]
    241.     [Student{id=4, name='赵六'}, Student{id=3, name='王五'}]
    242.     [Student{id=5, name='吴刚'}, Student{id=6, name='王如花'}]
    243.     [Student{id=7, name='李志静'}, Student{id=8, name='何王天'}]
    244.      */
    245. }

    例 22：

many-to-one上的fetch和lazy

  • fetch

    抓取策略，控制 SQL 语句格式。

    在这里 fetch 有两个可选值：

    select : 默认值，发送普通的 select 语句查询关联对象。

    join : 发送一条迫切左外连接查询关联对象。

  • lazy

    延迟加载，控制查询关联对象时是否使用懒加载。

    在这里 lazy 有三个可选值：

    proxy : 默认值，引用关联对象类的类级别加载策略。

    flase : 查询关联对象时，不使用延迟加载。

    no-proxy：不使用。

  • 示例

    1. /**
    2.  * com/zze/bean/Student.hbm.xml
    3.  * 默认值
    4.  * <many-to-one name="clazz" column="cid" class="com.zze.bean.Class" fetch="select" lazy="proxy"/>
    5.  *
    6.  * com/zze/bean/Class.hbm.xml
    7.  * <class name="com.zze.bean.Class" table="class" lazy="true">
    8.  */
    9. @Test
    10. public void test39(){
    11.     Session session = HibernateUtil.getCurrentSession();
    12.     Transaction transaction = session.beginTransaction();
    13.     Student student = session.get(Student.class, 1);
    14.     System.out.println(student.getClazz()); // 发送 SQL
    15.     transaction.commit();
    16.     /*
    17.     Hibernate:
    18.         select
    19.             student0_.id as id1_1_0_,
    20.             student0_.name as name2_1_0_,
    21.             student0_.age as age3_1_0_,
    22.             student0_.gender as gender4_1_0_,
    23.             student0_.cid as cid5_1_0_
    24.         from
    25.             student student0_
    26.         where
    27.             student0_.id=?
    28.     Hibernate:
    29.         select
    30.             class0_.id as id1_0_0_,
    31.             class0_.name as name2_0_0_
    32.         from
    33.             class class0_
    34.         where
    35.             class0_.id=?
    36.     Class{id=1, name='软件一班'}
    37.      */
    38. }
    39.  
    40. /**
    41.  * com/zze/bean/Student.hbm.xml
    42.  * 默认值
    43.  * <many-to-one name="clazz" column="cid" class="com.zze.bean.Class" fetch="select" lazy="proxy"/>
    44.  *
    45.  * com/zze/bean/Class.hbm.xml
    46.  * <class name="com.zze.bean.Class" table="class" lazy="false">
    47.  */
    48. @Test
    49. public void test40(){
    50.     Session session = HibernateUtil.getCurrentSession();
    51.     Transaction transaction = session.beginTransaction();
    52.     Student student = session.get(Student.class, 1);// 一次发送 2 条 SQL
    53.     System.out.println(student.getClazz());
    54.     transaction.commit();
    55.     /*
    56.     Hibernate:
    57.         select
    58.             student0_.id as id1_1_0_,
    59.             student0_.name as name2_1_0_,
    60.             student0_.age as age3_1_0_,
    61.             student0_.gender as gender4_1_0_,
    62.             student0_.cid as cid5_1_0_
    63.         from
    64.             student student0_
    65.         where
    66.             student0_.id=?
    67.     Hibernate:
    68.         select
    69.             class0_.id as id1_0_0_,
    70.             class0_.name as name2_0_0_
    71.         from
    72.             class class0_
    73.         where
    74.             class0_.id=?
    75.     Class{id=1, name='软件一班'}
    76.      */
    77. }
    78.  
    79. /**
    80.  * com/zze/bean/Student.hbm.xml
    81.  * fetch="join" 时，lazy 失效
    82.  * <many-to-one name="clazz" column="cid" class="com.zze.bean.Class" fetch="join" lazy="proxy"/>
    83.  */
    84. @Test
    85. public void test41(){
    86.     Session session = HibernateUtil.getCurrentSession();
    87.     Transaction transaction = session.beginTransaction();
    88.     Student student = session.get(Student.class, 1);// 一条关联 SQL
    89.     System.out.println(student.getClazz());
    90.     transaction.commit();
    91.     /*
    92.     Hibernate:
    93.         select
    94.             student0_.id as id1_1_0_,
    95.             student0_.name as name2_1_0_,
    96.             student0_.age as age3_1_0_,
    97.             student0_.gender as gender4_1_0_,
    98.             student0_.cid as cid5_1_0_,
    99.             class1_.id as id1_0_1_,
    100.             class1_.name as name2_0_1_
    101.         from
    102.             student student0_
    103.         left outer join
    104.             class class1_
    105.                 on student0_.cid=class1_.id
    106.         where
    107.             student0_.id=?
    108.     Class{id=1, name='软件一班'}
    109.      */
    110. }

    例 23：

批量抓取

一批指定数量的关联数据一起查询。

  1. /**
  2.  * 查询所有班级 及 所有班级下的学生信息
  3.  * 默认情况下，查询所有班级会发一条 SQL，然后每次查询班级上的学生也会发送一条 SQL
  4.  * 即如下有 4 个班级，会发 5 条SQL
  5.  */
  6. @Test
  7. public void test42() {
  8.     Session session = HibernateUtil.getCurrentSession();
  9.     Transaction transaction = session.beginTransaction();
  10.     Query query = session.createQuery("from Class");
  11.     List<Class> list = query.list();
  12.     for (Class clazz : list) {
  13.         System.out.println(clazz);
  14.         for (Student student : clazz.getStudents()) {
  15.             System.out.println(student);
  16.         }
  17.     }
  18.     transaction.commit();
  19.     /*
  20.     Hibernate:
  21.         select
  22.             class0_.id as id1_0_,
  23.             class0_.name as name2_0_
  24.         from
  25.             class class0_
  26.     Class{id=1, name='软件一班'}
  27.     Hibernate:
  28.         select
  29.             students0_.cid as cid5_1_0_,
  30.             students0_.id as id1_1_0_,
  31.             students0_.id as id1_1_1_,
  32.             students0_.name as name2_1_1_,
  33.             students0_.age as age3_1_1_,
  34.             students0_.gender as gender4_1_1_,
  35.             students0_.cid as cid5_1_1_
  36.         from
  37.             student students0_
  38.         where
  39.             students0_.cid=?
  40.     Student{id=1, name='李四'}
  41.     Student{id=2, name='张三'}
  42.     Class{id=2, name='软件二班'}
  43.     Hibernate:
  44.         select
  45.             students0_.cid as cid5_1_0_,
  46.             students0_.id as id1_1_0_,
  47.             students0_.id as id1_1_1_,
  48.             students0_.name as name2_1_1_,
  49.             students0_.age as age3_1_1_,
  50.             students0_.gender as gender4_1_1_,
  51.             students0_.cid as cid5_1_1_
  52.         from
  53.             student students0_
  54.         where
  55.             students0_.cid=?
  56.     Student{id=4, name='王五'}
  57.     Student{id=3, name='赵六'}
  58.     Class{id=3, name='汽修一班'}
  59.     Hibernate:
  60.         select
  61.             students0_.cid as cid5_1_0_,
  62.             students0_.id as id1_1_0_,
  63.             students0_.id as id1_1_1_,
  64.             students0_.name as name2_1_1_,
  65.             students0_.age as age3_1_1_,
  66.             students0_.gender as gender4_1_1_,
  67.             students0_.cid as cid5_1_1_
  68.         from
  69.             student students0_
  70.         where
  71.             students0_.cid=?
  72.     Student{id=5, name='王如花'}
  73.     Student{id=6, name='吴刚'}
  74.     Class{id=4, name='汽修二班'}
  75.     Hibernate:
  76.         select
  77.             students0_.cid as cid5_1_0_,
  78.             students0_.id as id1_1_0_,
  79.             students0_.id as id1_1_1_,
  80.             students0_.name as name2_1_1_,
  81.             students0_.age as age3_1_1_,
  82.             students0_.gender as gender4_1_1_,
  83.             students0_.cid as cid5_1_1_
  84.         from
  85.             student students0_
  86.         where
  87.             students0_.cid=?
  88.     Student{id=8, name='李志静'}
  89.     Student{id=7, name='何王天'}
  90.      */
  91. }
  92.  
  93. /**
  94.  * com/zze/bean/Class.hbm.xml
  95.  *
  96.  * <set name="students" cascade="save-update" batch-size="4">
  97.  * <p>
  98.  * 一次抓取 4 条，就只需要发送 2 次 SQL
  99.  * 一次查询所有班级，一次查询所有班级下的学生
  100.  */
  101. @Test
  102. public void test43() {
  103.     Session session = HibernateUtil.getCurrentSession();
  104.     Transaction transaction = session.beginTransaction();
  105.     Query query = session.createQuery("from Class");
  106.     List<Class> list = query.list();
  107.     for (Class clazz : list) {
  108.         System.out.println(clazz);
  109.         for (Student student : clazz.getStudents()) {
  110.             System.out.println(student);
  111.         }
  112.     }
  113.     transaction.commit();
  114.     /*
  115.     Hibernate:
  116.         select
  117.             class0_.id as id1_0_,
  118.             class0_.name as name2_0_
  119.         from
  120.             class class0_
  121.     Class{id=1, name='软件一班'}
  122.     Hibernate:
  123.         select
  124.             students0_.cid as cid5_1_1_,
  125.             students0_.id as id1_1_1_,
  126.             students0_.id as id1_1_0_,
  127.             students0_.name as name2_1_0_,
  128.             students0_.age as age3_1_0_,
  129.             students0_.gender as gender4_1_0_,
  130.             students0_.cid as cid5_1_0_
  131.         from
  132.             student students0_
  133.         where
  134.             students0_.cid in (
  135.                 ?, ?, ?, ?
  136.             )
  137.     Student{id=1, name='李四'}
  138.     Student{id=2, name='张三'}
  139.     Class{id=2, name='软件二班'}
  140.     Student{id=4, name='王五'}
  141.     Student{id=3, name='赵六'}
  142.     Class{id=3, name='汽修一班'}
  143.     Student{id=5, name='王如花'}
  144.     Student{id=6, name='吴刚'}
  145.     Class{id=4, name='汽修二班'}
  146.     Student{id=7, name='何王天'}
  147.     Student{id=8, name='李志静'}
  148.      */
  149. }
  150.  
  151. /**
  152.  * 查询所有学生 及 所有学生所属班级信息
  153.  * 默认情况下，查询所有学生会发送 1 条 SQL，然后每次查询每个学生的所属班级时也会发送一条 SQL，
  154.  * 有 8 个学生，但一共有 4 个班级，由于一级缓存的作用，查询班级需要发送 4 条 SQL
  155.  * 共发 5 条 SQL
  156.  */
  157. @Test
  158. public void test44() {
  159.     Session session = HibernateUtil.getCurrentSession();
  160.     Transaction transaction = session.beginTransaction();
  161.     Query query = session.createQuery("from Student");
  162.     List<Student> list = query.list();
  163.     for (Student student : list) {
  164.         System.out.println(student.getClazz());
  165.     }
  166.     transaction.commit();
  167.     /*
  168.     Hibernate:
  169.         select
  170.             student0_.id as id1_1_,
  171.             student0_.name as name2_1_,
  172.             student0_.age as age3_1_,
  173.             student0_.gender as gender4_1_,
  174.             student0_.cid as cid5_1_
  175.         from
  176.             student student0_
  177.     Hibernate:
  178.         select
  179.             class0_.id as id1_0_0_,
  180.             class0_.name as name2_0_0_
  181.         from
  182.             class class0_
  183.         where
  184.             class0_.id=?
  185.     Class{id=1, name='软件一班'}
  186.     Class{id=1, name='软件一班'}
  187.     Hibernate:
  188.         select
  189.             class0_.id as id1_0_0_,
  190.             class0_.name as name2_0_0_
  191.         from
  192.             class class0_
  193.         where
  194.             class0_.id=?
  195.     Class{id=2, name='软件二班'}
  196.     Class{id=2, name='软件二班'}
  197.     Hibernate:
  198.         select
  199.             class0_.id as id1_0_0_,
  200.             class0_.name as name2_0_0_
  201.         from
  202.             class class0_
  203.         where
  204.             class0_.id=?
  205.     Class{id=3, name='汽修一班'}
  206.     Class{id=3, name='汽修一班'}
  207.     Hibernate:
  208.         select
  209.             class0_.id as id1_0_0_,
  210.             class0_.name as name2_0_0_
  211.         from
  212.             class class0_
  213.         where
  214.             class0_.id=?
  215.     Class{id=4, name='汽修二班'}
  216.     Class{id=4, name='汽修二班'}
  217.      */
  218. }
  219.  
  220. /**
  221.  * com/zze/bean/Class.hbm.xml
  222.  * <class name="com.zze.bean.Class" table="class" batch-size="3">
  223.  * <p>
  224.  * many-to-one 关系时需在关联属性类映射文件下配置 batch-size
  225.  * <p>
  226.  * 查询所有学生 1 条 SQL，查询所有班级每次抓取 3 条，一共 4 个班级，会发 2 次 SQL
  227.  */
  228. @Test
  229. public void test45() {
  230.     Session session = HibernateUtil.getCurrentSession();
  231.     Transaction transaction = session.beginTransaction();
  232.     Query query = session.createQuery("from Student");
  233.     List<Student> list = query.list();
  234.     for (Student student : list) {
  235.         System.out.println(student.getClazz());
  236.     }
  237.     transaction.commit();
  238.     /*
  239.     Hibernate:
  240.         select
  241.             student0_.id as id1_1_,
  242.             student0_.name as name2_1_,
  243.             student0_.age as age3_1_,
  244.             student0_.gender as gender4_1_,
  245.             student0_.cid as cid5_1_
  246.         from
  247.             student student0_
  248.     Hibernate:
  249.         select
  250.             class0_.id as id1_0_0_,
  251.             class0_.name as name2_0_0_
  252.         from
  253.             class class0_
  254.         where
  255.             class0_.id in (
  256.                 ?, ?, ?
  257.             )
  258.     Class{id=1, name='软件一班'}
  259.     Class{id=1, name='软件一班'}
  260.     Class{id=2, name='软件二班'}
  261.     Class{id=2, name='软件二班'}
  262.     Class{id=3, name='汽修一班'}
  263.     Class{id=3, name='汽修一班'}
  264.     Hibernate:
  265.         select
  266.             class0_.id as id1_0_0_,
  267.             class0_.name as name2_0_0_
  268.         from
  269.             class class0_
  270.         where
  271.             class0_.id=?
  272.     Class{id=4, name='汽修二班'}
  273.     Class{id=4, name='汽修二班'}
  274.      */
  275. }

例 24：

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