Mybatis resultMap使用

    今天在項目中用了mybatis的resultMap。之前用的時候都是一些簡單的查詢，修改，分頁。此次涉及到了POJO對象之間的一對多和多對一的關係映射。

    mybatis有幾種使用方式, 我喜歡用mapper的方式,而後用spring來管理mybatis.

    開發工具是Eclipse jee, mybatis版本是3.0.5, mybatis-sprint-1.0.1

   

mybatis-config.xml 是mybatis的配置文件：

 

<configuration>
    <settings>
        <setting name="cacheEnabled" value="false" />
        <setting name="useGeneratedKeys" value="true" />
        <setting name="defaultExecutorType" value="REUSE" />
    </settings>
	<mappers>
        <mapper resource="com/exam/persistence/mapper/ClientMapper.xml" />
    </mappers>
</configuration>

applicationContext.xml:

 

<bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
	<property name="dataSource" ref="dataSource" />
	<property name="configLocation" value="/WEB-INF/mybatis-config.xml" />
</bean>

<bean id="clientMapper" class="org.mybatis.spring.mapper.MapperFactoryBean">
 
    <property name="mapperInterface" value="com.exam.persistence.mapper.ClientMapper" />
 
    <property name="sqlSessionFactory" ref="sqlSessionFactory" />
</bean>
 

配置文件就是這些了。主要的東西在下面：

業務邏輯涉及到三張表: Client, Subscriber, Account. 其中Client表和Subscriber表是多對一的關係. Client表和Account是一對多的關係。

 在com.example.persistence.mapper目錄下，須要建立兩個文件分別是：ClientMapper.java 和 ClientMapper.xml

對象映射關係主要在ClientMapper.xml中定義：

 

<?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.exam.persistence.mapper.ClientMapper">
    <resultMap id="clients" type="com.exam.entity.Clients">
    	<id property="externalId" column="externalId" />
    	<result property="id" column="id"/>
    	<result property="subscriptionId" column="subscriptionId"/>
    	<association property="subscription" column="subscriptionId" javaType="com.exam.entity.Subscription" select="selectSubscription"/>
    	<collection property="accounts" column="id" ofType="com.exam.entity.Accounts" select="selectAccounts"/>
    </resultMap>
    
    <select id="getClientByID" resultMap="clients" parameterType="java.lang.String">
       select 
           client.internal_id as id,
           client.external_id as externalId,
       from CLIENT client 
            left outer join SUBSCRIPTION subscription on client.subscription_id = subscription.subscription_id
            left outer join ACCOUNT accounts on client.internal_id = accounts.id
        where client.external_id = #{external_id}
    </select>
    
    <select id="selectAccounts" parameterType="int" resultType="com.exam.entity.Accounts">
    	select * from ACCOUNT where client_id=#{client_id}
    </select>
    <select id="selectSubscription" parameterType="java.lang.String" resultType="com.exam.entity.Subscription">
    	select * from SUBSCRIPTION where subscription_id = #{subscription_id}
    </select>
</mapper>

這個xml文件定義了一個resultMap id="clients". clients裏面包含了一個assoction(多對一)和一個collection(一對多). 這兩個分別對應了兩個select id.

 ClientMapper.java是一個interface：

import java.util.List;
import com.exam.entity.Clients;
public interface ClientMapper {
  public List<Clients> getClientByID(String external_id);
}

其中函數名"getClientByID"應該和ClientMapper.xml中的select id的值相同。

 在com.exam.entity目錄下面須要定義Clients, Accounts, Subscription 三個POJO類。就不在這裏寫POJO類了。

這樣咱們在service邏輯中就可使用ClientMapper.

 

public class ClientServiceImpl implements ClientService {
	private ClientMapper clientMapper;

	public ClientMapper getClientMapper() {
		return deviceMapper;
	}

	public void setClientMapper(ClientMapper clientMapper) {
		this.clientMapper = clientMapper;
	}

         @Override
	public List<Clients> getClientByID(String external_id) {
	    return getClientMapper().getClientByID(external_id);
	}
}咱們須要在applicationContext中把clientMapper注入到這個server類中就ok了。

先寫到這裏。