Mybatis表的關(guān)聯(lián)查詢詳情

更新時間：2022年09月21日 16:23:58 作者：姓蔡小朋

這篇文章主要介紹了Mybatis表的關(guān)聯(lián)查詢詳情，文章通過圍繞主題展開詳細的內(nèi)容介紹，具有一定的參考價值，需要的小伙伴可以參考一下

導(dǎo)語

關(guān)于＜resultMap＞標(biāo)簽映射，＜association＞＆＜collection＞的使用

什么時候用＜resultMap＞標(biāo)簽映射

1.當(dāng)我們查詢結(jié)果的返回值是由對象封裝的且對象中封裝了另一個對象時，用標(biāo)簽映射：具體細節(jié)見：Mybatis表的關(guān)聯(lián)查詢
2.當(dāng)我們的實體類名與數(shù)據(jù)庫列名不一致時，可以使用標(biāo)簽映射：

什么時候用<association>＆<collection>

當(dāng)我們的實體類中存有另一個實體類對象時，用<association>來映射內(nèi)部的實體類對象。
一對一、多對一的關(guān)聯(lián)關(guān)系一般用<association>。
當(dāng)我們的實體類中存有List或map集合是，用<collection>來映射。
一對多的關(guān)聯(lián)關(guān)系一般用<collection>。
無論是什么關(guān)聯(lián)關(guān)系，如果某方持有另一方的集合，則使用<collection>標(biāo)簽完成映射，如果某方持有另一方的對象，則使用<association>標(biāo)簽完成映射。
具體細節(jié)見：Mybatis表的關(guān)聯(lián)查詢

無論是什么關(guān)聯(lián)關(guān)系，如果某方持有另一方的集合，則使用標(biāo)簽完成映射，如果某方持有另一方的對象，則使用標(biāo)簽完成映射。

Mybatis表的關(guān)聯(lián)查詢

一對多查詢

根據(jù)顧客ID查詢顧客信息（一），同時將顧客名下所有訂單查出（多）。

實現(xiàn)思路：

創(chuàng)建顧客類，存儲顧客信息：注意我們在顧客類中用List集合封裝了顧客名下的訂單信息。

package com.user.pojo;

import java.util.List;

public class Customer {
    //customer表中的三個列
    private Integer id;
    private String name;
    private Integer age;
    //該客戶名下所有訂單集合
    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() {
    }
}

創(chuàng)建訂單類，存儲訂單信息：

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() {
    }
}

動態(tài)代理接口：

package com.user.mapper;

import com.user.pojo.Customer;

public interface CustomerMapper {
    //根據(jù)客戶id查詢客戶所有信息并同時查詢該客戶名下的所有訂單
    Customer getById(Integer id);
}

Mapper.xml文件：

因為我們的查詢結(jié)果包括該顧客信息和顧客所有的訂單信息，所以我們的返回值需要自定義一個map集合來存儲。我們這里使用 <resultMap>標(biāo)簽映射的方式創(chuàng)建我們的集合customermap，并將該集合作為我們的返回值類型。

<?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集合中存儲的數(shù)據(jù)單位，是customer對象
    id：該map結(jié)構(gòu)的標(biāo)識符
    -->
    <resultMap id="customermap" type="customer">
        <!--
        主鍵用id標(biāo)簽綁定，非主鍵用result標(biāo)簽綁定，集合用collection標(biāo)簽綁定
        property是customer類中的屬性，column是屬性對應(yīng)存儲的數(shù)據(jù)庫表中的列名，ofType是集合中存儲的數(shù)據(jù)類型
        -->
        <!--主鍵綁定-->
        <id  property="id" column="id"></id>
        <!--非主鍵綁定-->
        <result property="name" column="name"></result>
        <result property="age" column="age"></result>
        <!--訂單數(shù)據(jù)，不在customer表內(nèi)-->
        <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}為占位符，隨便寫的，表示所要查詢的顧客ID-->
</mapper>

測試程序：

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);
    }
}

其余基礎(chǔ)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>

多對一查詢

根據(jù)訂單ID查詢訂單信息及該訂單所屬的顧客的信息。

實現(xiàn)思路：

創(chuàng)建訂單類，存儲訂單信息：注意我們在訂單類中封裝了該訂單下的顧客的信息。

package com.user.pojo;

public class Order {
    //訂單信息
    private Integer id;
    private String orderNumber;
    private Double orderPrice;
    private Integer customer_id;
    //訂單所屬的客戶
    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() {
    }
}

創(chuàng)建顧客類，存儲顧客信息：

package com.user.pojo;

import java.util.List;

public class Customer {
    //顧客信息
    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() {
    }
}

動態(tài)代理接口：

    package com.user.mapper;

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

    public interface OrderMapper {
        //根據(jù)主鍵查訂單并同時查詢該訂單的客戶信息
        Order getById(Integer id);
    }

Mapper.xml文件：

因為我們的查詢結(jié)果包括該訂單信息和訂單所屬顧客的信息，所以我們的返回值需要自定義一個map集合來存儲。我們這里使用 <resultMap>標(biāo)簽映射的方式創(chuàng)建我們的集合customermap，并將該集合作為我們的返回值類型。

<?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集合中存儲的數(shù)據(jù)單位，是order對象
    id：該map結(jié)構(gòu)的標(biāo)識符
    -->
    <resultMap id="ordermap" type="order">
        <!--
        主鍵用id標(biāo)簽綁定，非主鍵用result標(biāo)簽綁定，集合用collection標(biāo)簽綁定，
        這里沒有用collection標(biāo)簽，而是用了association,因為返回的只有一行數(shù)據(jù)（一個顧客的信息），不需要集合存儲
        property是order類中的屬性，column是屬性對應(yīng)存儲的數(shù)據(jù)庫表中的列名，javaType是返回的數(shù)據(jù)用什么存儲
        -->
        <!--主鍵綁定-->
        <id  property="id" column="id"></id>
        <!--非主鍵綁定-->
        <result property="orderNumber" column="orderNumber"></result>
        <result property="orderPrice" column="orderPrice"></result>
        <result property="customer_id" column="customer_id"></result>
        <!--顧客數(shù)據(jù)，不在order表內(nèi)-->
        <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>

測試類：

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);
    }
}

其余基礎(chǔ)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>