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Mybatis关联查询

姓蔡小朋 人气:0

导语

关于<resultMap>标签映射,<association>&<collection>的使用

什么时候用<resultMap>标签映射

什么时候用<association>&<collection>

无论是什么关联关系,如果某方持有另一方的集合,则使用标签完成映射,如果某方持有另一方的对象,则使用标签完成映射。

Mybatis表的关联查询

一对多查询

根据顾客ID查询顾客信息(一),同时将顾客名下所有订单查出(多)。

实现思路:

创建顾客类,存储顾客信息:注意我们在顾客类中用List集合封装了顾客名下的订单信息。

package com.user.pojo;

import java.util.List;

public class Customer {
    //customer表中的三个列
    private Integer id;
    private String name;
    private Integer age;
    //该客户名下所有订单集合
    private List<Order> orderList;

    @Override
    public String toString() {
        return "Customer{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", age=" + age +
                ", orderList=" + orderList +
                '}';
    }

    public Integer getId() {
        return id;
    }

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

    public String getName() {
        return name;
    }

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

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    public List<Order> getOrderList() {
        return orderList;
    }

    public void setOrderList(List<Order> orderList) {
        this.orderList = orderList;
    }

    public Customer(Integer id, String name, Integer age, List<Order> orderList) {
        this.id = id;
        this.name = name;
        this.age = age;
        this.orderList = orderList;
    }

    public Customer() {
    }
}

创建订单类,存储订单信息:

package com.user.pojo;

public class Order {
    private Integer id;
    private String orderNumber;
    private Double orderPrice;

    @Override
    public String toString() {
        return "Order{" +
                "id=" + id +
                ", orderNumber='" + orderNumber + '\'' +
                ", orderPrice=" + orderPrice +
                '}';
    }

    public Integer getId() {
        return id;
    }

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

    public String getOrderNumber() {
        return orderNumber;
    }

    public void setOrderNumber(String orderNumber) {
        this.orderNumber = orderNumber;
    }

    public Double getOrderPrice() {
        return orderPrice;
    }

    public void setOrderPrice(Double orderPrice) {
        this.orderPrice = orderPrice;
    }

    public Order(Integer id, String orderNumber, Double orderPrice) {
        this.id = id;
        this.orderNumber = orderNumber;
        this.orderPrice = orderPrice;
    }

    public Order() {
    }
}

动态代理接口:

package com.user.mapper;

import com.user.pojo.Customer;

public interface CustomerMapper {
    //根据客户id查询客户所有信息并同时查询该客户名下的所有订单
    Customer getById(Integer id);
}

Mapper.xml文件:

因为我们的查询结果包括该顾客信息和顾客所有的订单信息,所以我们的返回值需要自定义一个map集合来存储。我们这里使用 <resultMap>标签映射的方式创建我们的集合customermap,并将该集合作为我们的返回值类型。

<?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="com.user.mapper.CustomerMapper">
    <!--
    type:map集合中存储的数据单位,是customer对象
    id:该map结构的标识符
    -->
    <resultMap id="customermap" type="customer">
        <!--
        主键用id标签绑定,非主键用result标签绑定,集合用collection标签绑定
        property是customer类中的属性,column是属性对应存储的数据库表中的列名,ofType是集合中存储的数据类型
        -->
        <!--主键绑定-->
        <id  property="id" column="id"></id>
        <!--非主键绑定-->
        <result property="name" column="name"></result>
        <result property="age" column="age"></result>
        <!--订单数据,不在customer表内-->
        <collection property="orderList" ofType="order">
            <id property="id" column="id"></id>
            <result property="orderNumber" column="orderNumber"></result>
            <result property="orderPrice" column="orderPrice"></result>
        </collection>
    </resultMap>
    <select id="getById" parameterType="Integer" resultMap="customermap">
        select customer.id ,name,age ,orders.id ,orderNumber ,orderPrice ,customer_id
        from customer left join orders on customer.id = orders.customer_id
        where customer.id = #{id}
    </select>
    <!--#{id}为占位符,随便写的,表示所要查询的顾客ID-->
</mapper>

测试程序:

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

public class MyTest {
    SqlSession sqlSession;
    CustomerMapper customerMapper;
    @Before
    public void openSqlSession() throws IOException {
        InputStream in = Resources.getResourceAsStream("SqlMapConfig.xml");
        SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(in);
        sqlSession = factory.openSession();
        customerMapper = sqlSession.getMapper(CustomerMapper.class);
    }
    @After
    public void closeSqlSession(){
        sqlSession.close();
    }
    @Test
    public  void testGetCustomerById(){
        Customer customer = customerMapper.getById(1);
        System.out.println(customer);
    }
}

其余基础配置文件SqlMapConfig.xml:

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
    <properties resource="jdbc.properties"></properties>
    <settings>
        <setting name="logImpl" value="STDOUT_LOGGING"/>
    </settings>
    <typeAliases>
        <package name="com.user.pojo"/>
        <package name="com.user.mapper"/>
    </typeAliases>
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"></transactionManager>
            <dataSource type="POOLED">
                <property name="driver" value="${jdbc.driverClassName}"/>
                <property name="url" value="${jdbc.url}"/>
                <property name="username" value="${jdbc.username}"/>
                <property name="password" value="${jdbc.password}"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <package name="com.user.mapper"></package>
    </mappers>
</configuration>

多对一查询

根据订单ID查询订单信息及该订单所属的顾客的信息。

实现思路:

创建订单类,存储订单信息:注意我们在订单类中封装了该订单下的顾客的信息。

package com.user.pojo;

public class Order {
    //订单信息
    private Integer id;
    private String orderNumber;
    private Double orderPrice;
    private Integer customer_id;
    //订单所属的客户
    private Customer customer;

    @Override
    public String toString() {
        return "Order{" +
                "id=" + id +
                ", orderNumber='" + orderNumber + '\'' +
                ", orderPrice=" + orderPrice +
                ", customer_id=" + customer_id +
                ", customer=" + customer +
                '}';
    }

    public Integer getId() {
        return id;
    }

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

    public String getOrderNumber() {
        return orderNumber;
    }

    public void setOrderNumber(String orderNumber) {
        this.orderNumber = orderNumber;
    }

    public Double getOrderPrice() {
        return orderPrice;
    }

    public void setOrderPrice(Double orderPrice) {
        this.orderPrice = orderPrice;
    }

    public Integer getCustomer_id() {
        return customer_id;
    }

    public void setCustomer_id(Integer customer_id) {
        this.customer_id = customer_id;
    }

    public Customer getCustomer() {
        return customer;
    }

    public void setCustomer(Customer customer) {
        this.customer = customer;
    }

    public Order(Integer id, String orderNumber, Double orderPrice, Integer customer_id, Customer customer) {
        this.id = id;
        this.orderNumber = orderNumber;
        this.orderPrice = orderPrice;
        this.customer_id = customer_id;
        this.customer = customer;
    }
    public Order() {
    }
}

创建顾客类,存储顾客信息:

package com.user.pojo;

import java.util.List;

public class Customer {
    //顾客信息
    private Integer id;
    private String name;
    private Integer age;

    @Override
    public String toString() {
        return "Customer{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", age=" + age +
                '}';
    }

    public Integer getId() {
        return id;
    }

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

    public String getName() {
        return name;
    }

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

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    public Customer(Integer id, String name, Integer age) {
        this.id = id;
        this.name = name;
        this.age = age;
    }
    public Customer() {
    }
}

动态代理接口:

    package com.user.mapper;

    import com.user.pojo.Customer;
    import com.user.pojo.Order;

    public interface OrderMapper {
        //根据主键查订单并同时查询该订单的客户信息
        Order getById(Integer id);
    }

Mapper.xml文件:

因为我们的查询结果包括该订单信息和订单所属顾客的信息,所以我们的返回值需要自定义一个map集合来存储。我们这里使用 <resultMap>标签映射的方式创建我们的集合customermap,并将该集合作为我们的返回值类型。

<?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="com.user.mapper.OrderMapper">
    <!--
    type:map集合中存储的数据单位,是order对象
    id:该map结构的标识符
    -->
    <resultMap id="ordermap" type="order">
        <!--
        主键用id标签绑定,非主键用result标签绑定,集合用collection标签绑定,
        这里没有用collection标签,而是用了association,因为返回的只有一行数据(一个顾客的信息),不需要集合存储
        property是order类中的属性,column是属性对应存储的数据库表中的列名,javaType是返回的数据用什么存储
        -->
        <!--主键绑定-->
        <id  property="id" column="id"></id>
        <!--非主键绑定-->
        <result property="orderNumber" column="orderNumber"></result>
        <result property="orderPrice" column="orderPrice"></result>
        <result property="customer_id" column="customer_id"></result>
        <!--顾客数据,不在order表内-->
        <association property="customer" javaType="customer">
            <id property="id" column="id"></id>
            <result property="name" column="name"></result>
            <result property="age" column="age"></result>
        </association>
    </resultMap>
    <select id="getById" parameterType="Integer" resultMap="ordermap">
        select orders.id ,orderNumber ,orderPrice ,customer_id ,customer.id ,name,age
        from orders left join customer on orders.customer_id = customer.id
        where orders.id = #{id}
    </select>
</mapper>

测试类:

package com.user;

import com.user.mapper.OrderMapper;
import com.user.pojo.Order;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;

import java.io.IOException;
import java.io.InputStream;

public class MyTest {
    SqlSession sqlSession;
    OrderMapper orderMapper;
    @Before
    public void openSqlSession() throws IOException {
        InputStream in = Resources.getResourceAsStream("SqlMapConfig.xml");
        SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(in);
        sqlSession = factory.openSession();
        orderMapper = sqlSession.getMapper(OrderMapper.class);
    }
    @After
    public void closeSqlSession(){
        sqlSession.close();
    }
    @Test
    public void testGetOrderById(){
        Order order = orderMapper.getById(11);
        System.out.println(order);
    }
}

其余基础配置文件:

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
    <properties resource="jdbc.properties"></properties>
    <settings>
        <setting name="logImpl" value="STDOUT_LOGGING"/>
    </settings>
    <typeAliases>
        <package name="com.user.pojo"/>
        <package name="com.user.mapper"/>
    </typeAliases>
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"></transactionManager>
            <dataSource type="POOLED">
                <property name="driver" value="${jdbc.driverClassName}"/>
                <property name="url" value="${jdbc.url}"/>
                <property name="username" value="${jdbc.username}"/>
                <property name="password" value="${jdbc.password}"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <package name="com.user.mapper"></package>
    </mappers>
</configuration>

一对一查询

同多对一。

实体类:

动态代理接口:

mapper.xml文件:

多对多查询

多对多关联中,需要通过中间表化解关联关系。中间表描述两张主键表的关联。

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