笔记52 Mybatis快速入门（三）

一、更多查询

1.模糊查询

修改Category.xml，提供listCategoryByName查询语句select * from category where name like concat('%',#{0},'%')。concat('%',#{0},'%') 这是mysql的写法，如果是oracle，写法是select * from category_ where name like '%'||#{0}||'%'。

 <select id="listCategoryByName" parameterType="string" resultType="Category">
         select * from   category  where name like concat('%',#{0},'%')
 </select>

     private void queryByName() throws IOException {
         create();
         List<Category> categories = session.selectList("listCategoryByName", "i");
         for (Category category : categories) {
             System.out.println(category.getName());
         }
         close();
     }

2.多条件查询

结合前面的模糊查询，多一个限定id的条件。因为是多个参数，而selectList方法又只接受一个参数对象，所以需要把多个参数放在Map里，然后把这个Map对象作为参数传递进去。

     private void queryByNameId() throws IOException {
         create();
         Map<String, Object> params = new HashMap<String, Object>();
         params.put("id", 8);
         params.put("name", "xiao");
         List<Category> categories = session.selectList("listCategoryByNameId", params);
         for (Category category : categories) {
             System.out.println(category.getName());
         }
         close();
     }

     <select id="listCategoryByNameId" parameterType="map"
         resultType="Category">
         select * from category where id>#{id} and name like
         concat('%',#{0},'%')
     </select>

二、Mybatis的关系映射

1.一对多（一个分类对应多个产品）

<1>创建产品表以及产品表对应的实体。

 package mybatis.pojo;

 public class Product {
     private int id;
     private String name;
     private float price;

     public int getId() {
         return id;
     }

     public void setId(int id) {
         this.id = id;
     }

     public String getName() {
         return name;
     }

     public void setName(String name) {
         this.name = name;
     }

     public float getPrice() {
         return price;
     }

     public void setPrice(float price) {
         this.price = price;
     }

     public String toString() {
         return "Product [id=" + id + ", name=" + name + ", price=" + price + "]";
     }

 }

<2>修改Category实体类，提供product集合。

 package mybatis.pojo;

 import java.util.List;

 public class Category {
     private int id;
     private String name;
     private List<Product> products;

     public int getId() {
         return id;
     }

     public void setId(int id) {
         this.id = id;
     }

     public String getName() {
         return name;
     }

     public void setName(String name) {
         this.name = name;
     }

     public List<Product> getProducts() {
         return products;
     }

     public void setProducts(List<Product> products) {
         this.products = products;
     }

     public String toString() {
         return "Category [id=" + id + ", name=" + name + "]";
     }
 }

<3>修改Category.xml

通过left join关联查询，对Category和Product表进行关联查询。与前面学习的有所区别，这里不是用的resultType, 而是resultMap，通过resultMap把数据取出来放在对应的对象属性里。

注： Category的id字段和Product的id字段同名，Mybatis不知道谁是谁的，所以需要通过取别名cid,pid来区分，name字段同理。

 <?xml version="1.0" encoding="UTF-8"?>
 <!DOCTYPE mapper
     PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">

 <mapper namespace="mybatis.pojo">
     <resultMap type="Category" id="categoryBean">
         <id column="cid" property="id" />
         <result column="cname" property="name" />

         <!-- 一对多关系 -->
         <!-- property:指定的是集合属性的值，ofType：指的是集合中元素的类型 -->
         <collection property="products" ofType="Product">
             <id column="pid" property="id"></id>
             <result column="pname" property="name" />
             <result column="price" property="price" />
         </collection>
     </resultMap>
     <!-- 关联查询分类和产品表 -->
     <select id="listCategory" resultMap="categoryBean">
         select c.*, p.*, c.id 'cid', p.id 'pid', c.name 'cname', p.name 'pname' from
         category c left join product p on c.id = p.cid
     </select>
 </mapper>

<4>测试

 package mybatis.test;

 import java.io.IOException;
 import java.io.InputStream;
 import java.util.List;

 import org.apache.ibatis.session.SqlSession;
 import org.apache.ibatis.session.SqlSessionFactory;
 import org.apache.ibatis.session.SqlSessionFactoryBuilder;

 import mybatis.pojo.Category;
 import mybatis.pojo.Product;

 public class testOneToMany {

     public static void main(String[] args) throws IOException {
         // TODO Auto-generated method stub
         String resource = "mybatis-config.xml";
         InputStream inputStream = org.apache.ibatis.io.Resources.getResourceAsStream(resource);
         SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
         SqlSession session = sqlSessionFactory.openSession();
         List<Category> categories = session.selectList("listCategory");
         for (Category c : categories) {
             System.out.println(c);
             List<Product> products = c.getProducts();
             for (Product product : products) {
                 System.out.println("\t" + product.toString());
             }
         }
         session.commit();
         session.close();
     }

 }

2.多对一（多个产品对应一个分类）

<1>修改Product.java，增加category属性

 package mybatis.pojo;

 import java.util.List;

 public class Category {
     private int id;
     private String name;
     private List<Product> products;

     public int getId() {
         return id;
     }

     public void setId(int id) {
         this.id = id;
     }

     public String getName() {
         return name;
     }

     public void setName(String name) {
         this.name = name;
     }

     public List<Product> getProducts() {
         return products;
     }

     public void setProducts(List<Product> products) {
         this.products = products;
     }

     public String toString() {
         return "Category [id=" + id + ", name=" + name + "]";
     }
 }

<2>新增Product.xml

 <?xml version="1.0" encoding="UTF-8"?>
 <!DOCTYPE mapper
     PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">

 <mapper namespace="mybatis.pojo">

     <select id="getProduct" parameterType="int" resultType="Product">
         select *
         from product where id= #{id}
     </select>

     <update id="updateProduct" parameterType="map">
         update product
         set cid=#{cid} where id=#{pid}
     </update>

     <update id="updateProduct2" parameterType="Product">
         update product
         set cid=#{category.id} where id=#{id}
     </update>

     <resultMap type="Product" id="productBean">
         <id column="pid" property="id" />
         <result column="pname" property="name" />
         <result column="price" property="price" />

         <!-- 多对一关系 -->
         <!-- property:指定的是集合属性的值，ofType：指的是集合中元素的类型 -->
         <association property="category" javaType="Category">
             <id column="cid" property="id" />
             <result column="cname" property="name" />
         </association>
     </resultMap>
     <!-- 关联查询分类和产品表 -->
     <select id="listProduct" resultMap="productBean">
         select c.*, p.*, c.id 'cid',
         p.id 'pid', c.name 'cname', p.name 'pname' from
         category c left join
         product p on c.id = p.cid
     </select>
 </mapper>

通过listProduct配置关联查询的sql语句。然后通过resultMap ，进行字段和属性的对应。使用association 进行多对一关系关联，指定表字段名称与对象属性名称的一一对应关系。

注： Category的id 字段 和Product的id字段同名，Mybatis不知道谁是谁的，所以需要通过取别名cid,pid来区分。name字段同理。

<3>在mybatis-config.xml中增加对于Product.xml的映射

 <mapper resource="mybatis/pojo/Product.xml" />

<4>测试

 package mybatis.test;

 import java.io.IOException;
 import java.io.InputStream;
 import java.util.List;

 import org.apache.ibatis.session.SqlSession;
 import org.apache.ibatis.session.SqlSessionFactory;
 import org.apache.ibatis.session.SqlSessionFactoryBuilder;

 import mybatis.pojo.Category;
 import mybatis.pojo.Product;

 public class testManyToOne {

     public static void update() throws IOException {
         String resource = "mybatis-config.xml";
         InputStream inputStream = org.apache.ibatis.io.Resources.getResourceAsStream(resource);
         SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
         SqlSession session = sqlSessionFactory.openSession();

         Category category = session.selectOne("getCategory", 1);
         Product product = session.selectOne("getProduct", 6);
         product.setCategory(category);
         session.update("updateProduct2", product);

         // Map<String, Integer> params = new HashMap<String, Integer>();
         // params.put("cid", category.getId());
         // params.put("pid", product.getId());
         //
         // session.update("updateProduct", params);

         session.commit();
         session.close();
     }

     public static void main(String[] args) throws IOException {
         // TODO Auto-generated method stub
         update();
         String resource = "mybatis-config.xml";
         InputStream inputStream = org.apache.ibatis.io.Resources.getResourceAsStream(resource);
         SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
         SqlSession session = sqlSessionFactory.openSession();

         List<Product> products = session.selectList("listProduct");
         for (Product product : products) {
             System.out.println(product + "\t对应的分类是：" + product.getCategory());

         }

         session.commit();
         session.close();

     }

 }

练习：修改product(id=5)对应的类别为category(id=1)

两种解决思路

<1>首先查询id=5的product，再查询id=1的category，然后调用setCategory方法设置类别，然后对product进行更新操作。

<2>首先查询id=5的product，然后直接设置参数对product进行修改。

①先准备必要的sql语句。

Product.xml中

在updateProduct2中，因为product的成员变量中包含catergory对象，所以直接使用category.id获取类别的id。

     <select id="getProduct" parameterType="int" resultType="Product">
         select *
         from product where id= #{id}
     </select>

     <update id="updateProduct" parameterType="map">
         update product
         set cid=#{cid} where id=#{pid}
     </update>

     <update id="updateProduct2" parameterType="Product">
         update product
         set cid=#{category.id} where id=#{id}
     </update>

Category.xml中

     <select id="getCategory" parameterType="int" resultType="Category">
         select *
         from category where id= #{id}
     </select>

②测试

第一种思路

     public static void update() throws IOException {
         String resource = "mybatis-config.xml";
         InputStream inputStream = org.apache.ibatis.io.Resources.getResourceAsStream(resource);
         SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
         SqlSession session = sqlSessionFactory.openSession();

         Category category = session.selectOne("getCategory", 1);
         Product product = session.selectOne("getProduct", 6);
         product.setCategory(category);
         session.update("updateProduct2", product);

         session.commit();
         session.close();
     }

第二种思路

     public static void update() throws IOException {
         String resource = "mybatis-config.xml";
         InputStream inputStream = org.apache.ibatis.io.Resources.getResourceAsStream(resource);
         SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
         SqlSession session = sqlSessionFactory.openSession();

         Product product = session.selectOne("getProduct", 6);
          Map<String, Integer> params = new HashMap<String, Integer>();
          params.put("cid", 1);
          params.put("pid", product.getId());

          session.update("updateProduct", params);
         session.commit();
         session.close();
     }

3.多对多（一张订单可以包含多种产品，一种产品可以出现在多张订单中）

为了维系多对多关系，必须要一个中间表。 在这里我们使用订单项(OrderItem)表来作为中间表。

<1>建立order表，order_item表

<2>添加数据

 INSERT INTO order_ VALUES (1,'code000A');
 INSERT INTO order_ VALUES (2,'code000B');

 INSERT INTO order_item VALUES (null, 1, 1, 100);
 INSERT INTO order_item VALUES (null, 1, 2, 100);
 INSERT INTO order_item VALUES (null, 1, 3, 100);
 INSERT INTO order_item VALUES (null, 2, 2, 100);
 INSERT INTO order_item VALUES (null, 2, 3, 100);
 INSERT INTO order_item VALUES (null, 2, 4, 100); 

<3>添加实体类Order和OrderItem

①Order.java

 package mybatis.pojo;

 import java.util.List;

 public class Order {
     private int id;
     private String code;
     private List<OrderItem> orderItems;

     public List<OrderItem> getOrderItems() {
         return orderItems;
     }

     public void setOrderItems(List<OrderItem> orderItems) {
         this.orderItems = orderItems;
     }

     public int getId() {
         return id;
     }

     public void setId(int id) {
         this.id = id;
     }

     public String getCode() {
         return code;
     }

     public void setCode(String code) {
         this.code = code;
     }

 }

②OrderItem.java

 package mybatis.pojo;

 public class OrderItem {
     private int id;
     private int number;
     private Order order;
     private Product product;

     public int getId() {
         return id;
     }

     public void setId(int id) {
         this.id = id;
     }

     public int getNumber() {
         return number;
     }

     public void setNumber(int number) {
         this.number = number;
     }

     public Order getOrder() {
         return order;
     }

     public void setOrder(Order order) {
         this.order = order;
     }

     public Product getProduct() {
         return product;
     }

     public void setProduct(Product product) {
         this.product = product;
     }

 }

<4>映射文件

①Order.xml

 <?xml version="1.0" encoding="UTF-8"?>
 <!DOCTYPE mapper
     PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">

 <mapper namespace="mybatis.pojo">
     <resultMap type="Order" id="orderBean">
         <id column="oid" property="id" />
         <result column="code" property="code" />

         <collection property="orderItems" ofType="OrderItem">
             <id column="oiid" property="id" />
             <result column="number" property="number" />
             <association property="product" javaType="Product">
                 <id column="pid" property="id" />
                 <result column="pname" property="name" />
                 <result column="price" property="price" />
             </association>
         </collection>
     </resultMap>

     <select id="listOrder" resultMap="orderBean">
         select o.*,p.*,oi.*, o.id
         'oid', p.id 'pid', oi.id 'oiid', p.name 'pname'
         from order_ o
         left join
         order_item oi on o.id =oi.oid
         left join product p on p.id = oi.pid
     </select>
     <select id="getOrder" resultMap="orderBean">
         select o.*,p.*,oi.*, o.id 'oid', p.id 'pid', oi.id 'oiid', p.name 'pname'
         from order_ o
         left join order_item oi on o.id =oi.oid
         left join product p on p.id = oi.pid
         where o.id = #{id}
     </select>
 </mapper>

②Product.xml

 <?xml version="1.0" encoding="UTF-8"?>
 <!DOCTYPE mapper
     PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">

 <mapper namespace="mybatis.pojo">

     <!--
     <select id="getProduct" parameterType="int" resultType="Product">
         select *
         from product where id= #{id}
     </select>-->

     <update id="updateProduct" parameterType="map">
         update product
         set
         cid=#{cid} where id=#{pid}
     </update>

     <update id="updateProduct2" parameterType="Product">
         update product
         set
         cid=#{category.id} where id=#{id}
     </update>

     <resultMap type="Product" id="productBean">
         <id column="pid" property="id" />
         <result column="pname" property="name" />
         <result column="price" property="price" />

         <!-- 多对一关系 -->
         <!-- property:指定的是集合属性的值，ofType：指的是集合中元素的类型 -->
         <association property="category" javaType="Category">
             <id column="cid" property="id" />
             <result column="cname" property="name" />
         </association>
     </resultMap>
     <!-- 关联查询分类和产品表 -->
     <select id="listProduct" resultMap="productBean">
         select c.*, p.*, c.id 'cid',
         p.id 'pid', c.name 'cname', p.name 'pname' from
         category c left join
         product p on c.id = p.cid
     </select>
     <select id="getProduct" resultMap="productBean">
         select c.*, p.*, c.id 'cid', p.id 'pid', c.name 'cname', p.name 'pname'
         from category c
         left join product p on c.id = p.cid
         where p.id = #{id}
     </select>
 </mapper>

③OrderItem.xml

 <?xml version="1.0" encoding="UTF-8"?>
 <!DOCTYPE mapper
     PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">

 <mapper namespace="mybatis.pojo">
     <insert id="addOrderItem" parameterType="OrderItem">
         insert into order_item
         values(null,#{order.id},#{product.id},#{number})
     </insert>
     <insert id="deleteOrderItem" parameterType="OrderItem">
         delete from order_item
         where oid = #{order.id} and pid = #{product.id}
     </insert>
 </mapper>

<5>修改mybatis-config.xml

 <mapper resource="mybatis/pojo/Order.xml" />
 <mapper resource="mybatis/pojo/OrderItem.xml" />

<6>查询操作

查询出所有的订单，然后遍历每个订单下的多条订单项，以及订单项对应的产品名称，价格，购买数量。通过Order.xml的listOrder对应的sql语句进行查询：

     <select id="listOrder" resultMap="orderBean">
         select o.*,p.*,oi.*, o.id
         'oid', p.id 'pid', oi.id 'oiid', p.name 'pname'
         from order_ o
         left join
         order_item oi on o.id =oi.oid
         left join product p on p.id = oi.pid
     </select>

联合order_, order_item_, product_ 三张表进行查询

     <resultMap type="Order" id="orderBean">
         <id column="oid" property="id" />
         <result column="code" property="code" />

         <collection property="orderItems" ofType="OrderItem">
             <id column="oiid" property="id" />
             <result column="number" property="number" />
             <association property="product" javaType="Product">
                 <id column="pid" property="id" />
                 <result column="pname" property="name" />
                 <result column="price" property="price" />
             </association>
         </collection>
     </resultMap>

     private static void listOrder(SqlSession session) {
         List<Order> orders = session.selectList("listOrder");
         for (Order order : orders) {
             System.out.println(order.getCode());
             List<OrderItem> orderItems = order.getOrderItems();
             for (OrderItem orderItem : orderItems) {
                 System.out.format("\t%s\t%f\t%d\n", orderItem.getProduct().getName(), orderItem.getProduct().getPrice(),
                         orderItem.getNumber());
             }
         }
     }

<7>建立关系

　　建立了让订单000A和产品z建立了关系。首先通过id分别获取Ordre对象和Product对象，然后创建一个新的OrderItem对象，接着设置Order，设置Product，设置数量，最后调用"addOrderItem" 对应的sql语句插入数据。

     private static void addOrderItem(SqlSession session) {
         Order order = session.selectOne("getOrder", 1);
         Product product = session.selectOne("getProduct", 6);
         OrderItem orderItem = new OrderItem();
         orderItem.setProduct(product);
         orderItem.setOrder(order);
         orderItem.setNumber(200);

         session.insert("addOrderItem", orderItem);
     }

addOrderItem调用insert into 语句插入一条OrderItem记录：

     <insert id="addOrderItem" parameterType="OrderItem">
         insert into order_item
         values(null,#{order.id},#{product.id},#{number})
     </insert> 

<8>删除关系

删除了订单00A和产品z的关系，再次查询，就看不到产品z了。删除关系的时候，通过订单id(1)和产品id(6)进行删除。其实所谓的删除关系，就是删除掉OrderItem记录。

     private static void deleteOrderItem(SqlSession session) {
         Order order = session.selectOne("getOrder", 1);
         Product product = session.selectOne("getProduct", 6);
         OrderItem orderItem = new OrderItem();
         orderItem.setProduct(product);
         orderItem.setOrder(order);
         session.delete("deleteOrderItem", orderItem);
     }

练习：删除订单A，那么就应该删除订单A在订单项里所对应的数据。

通过Mybatis执行多条sql语句需要增加一个参数：allowMultiQueries，多条语句之间用分号隔开。

 <property name="url" value="jdbc:mysql://localhost:3306/test2?characterEncoding=UTF-8&amp;allowMultiQueries=true" />

     <delete id="deleteOrder" parameterType="Order">
         delete from
         order_ where code = #{code};
         delete from
         order_item
         where oid = #{id}
     </delete>

     private static void deleteOrder(SqlSession session) {
         Order order = session.selectOne("getOrder", 1);
         session.delete("deleteOrder", order);
     }