HOL的多表查询——内连接、外连接

1、内连接：

由于学生和班级是多对一的关系，班级对应学生是一对多的关系，因此，需要先对学生和班级进行配置。

（1）创建Student类（多的一方）：

package pers.zhb.domain;
public class Student {
    private int studentno;
    private String sname;
    private String sex;
    private String birthday;
    private String classno;
    private Float point;
    private String phone;
    private Clas aClas;
    public Student(){//无参的构造方法
    }
    public Clas getaClas() {
        return aClas;
    }
    public void setaClas(Clas aClas) {
        this.aClas = aClas;
    }
    public int getStudentno() {
        return studentno;
    }

    public void setStudentno(int studentno) {
        this.studentno = studentno;
    }

    public String getSname() {
        return sname;
    }

    public void setSname(String sname) {
        this.sname = sname;
    }

    public String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }

    public String getBirthday() {
        return birthday;
    }

    public void setBirthday(String birthday) {
        this.birthday = birthday;
    }

    public String getClassno() {
        return classno;
    }

    public void setClassno(String classno) {
        this.classno = classno;
    }

    public float getPoint() {
        return point;
    }

    public void setPoint(float point) {
        this.point = point;
    }

    public String getPhone() {
        return phone;
    }

    public void setPhone(String phone) {
        this.phone = phone;
    }

    @Override
    public String toString() {
        return "Student{" +
                "studentno='" + studentno + '\'' +
                ", sname='" + sname + '\'' +
                ", sex='" + sex + '\'' +
                ", birthday='" + birthday + '\'' +
                ", classno='" + classno + '\'' +
                ", point=" + point +
                ", phone='" + phone + '\'' +
                '}';
    }
}

　配置文件：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC
        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
        "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="pers.zhb.domain">
    <class name="Student" table="student">
        <id name="studentno" column="studentno">
            <generator class="native"></generator>
        </id>
        <property name="birthday" column="birthday"></property>
        <property name="classno" column="classno" insert="false" update="false"></property>
        <property name="phone" column="phone"></property>
        <property name="sex" column="sex"></property>
        <property name="sname" column="sname"></property>
        <property name="point" column="point"></property>
        <many-to-one name="aClas" column="classno" class="Clas"></many-to-one>
    </class>
</hibernate-mapping>

　　

（2）创建Clas类（班级，代表1的一方）：

package pers.zhb.domain;
import java.util.HashSet;
import java.util.Set;
public class Clas {
    private String classno;
    private String department;
    private String monitor;
    private String classname;
    private Set<Student> students=new HashSet<Student>();//使用set集合表达一对多关系,一个班级对应多个学生
    public String getClassno() {
        return classno;
    }

    public void setClassno(String classno) {
        this.classno = classno;
    }

    public String getDepartment() {
        return department;
    }

    public void setDepartment(String department) {
        this.department = department;
    }

    public String getMonitor() {
        return monitor;
    }

    public void setMonitor(String monitor) {
        this.monitor = monitor;
    }
    public void setClassname(String classname) {
        this.classname = classname;
    }
    public String getClassname() {
        return classname;
    }

    public Set<Student> getStudents() {
        return students;
    }

    public void setStudents(Set<Student> students) {
        this.students = students;
    }

    @Override
    public String toString() {
        return "Clas{" +
                "classno=" + classno +
                ", department='" + department + '\'' +
                ", monitor='" + monitor + '\'' +
                ", classname='" + classname + '\'' +
                ", students=" + students +
                '}';
    }

}　　

配置文件：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC
        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
        "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="pers.zhb.domain">
    <class name="Clas" table="class">
        <id name="classno" column="classno">
            <generator class="native"></generator>
        </id><!--主键-->
        <property name="department" column="department"></property>
        <property name="monitor" column="monitor"></property>
        <property name="classname" column="classname"></property>
        <set name="students" table="student"><!--一对多关系配置-->
            <key column="classno" update="false"></key><!--指定了集合表的外键-->
            <one-to-many class="Student"></one-to-many>
        </set>
    </class>
</hibernate-mapping>

　（3）测试HQL的内连接：

 public static void testSel() {
        Session session = HibernateUtils.openSession();
        Transaction transaction = session.beginTransaction();
        String hql="from Clas c inner join c.students";
        Query query=session.createQuery(hql);
        List<Object[]> list=query.list();
        for(Object[] arr:list){
            System.out.println(Arrays.toString(arr));
        }
        transaction.commit();
        session.

表中数据：

学生表：

班级表：

测试结果：

通过SQL语句直接查询：

SELECT *
FROM student,class
WHERE student.classno=class.classno
AND student.classno='tx171'

（4）迫切内连接：

 public static void testSel() {
        Session session = HibernateUtils.openSession();
        Transaction transaction = session.beginTransaction();
        String hql="from Clas c inner join fetch c.students";
        Query query=session.createQuery(hql);
        List<Clas> list=query.list();

        transaction.commit();
        session.close();//游离状态
    }

与内连接不同的是，迫切内连接是把学生对象直接封装到了班级对象中了，而内连接则是将两个对象存储到了数组中。

2、外连接：

（1）左外连接：

public static void testSel() {
        Session session = HibernateUtils.openSession();
        Transaction transaction = session.beginTransaction();
        String hql="from Clas c left join  c.students";
        Query query=session.createQuery(hql);
        List<Clas> list=query.list();
        System.out.println(list);
        transaction.commit();
        session.close();//游离状态
    }

（2）右外连接：

 public static void testSel() {
        Session session = HibernateUtils.openSession();
        Transaction transaction = session.beginTransaction();
        String hql="from Clas c right join  c.students";
        Query query=session.createQuery(hql);
        List<Clas> list=query.list();
        System.out.println(list);
        transaction.commit();
        session.close();//游离状态
    }