mybatis collection和association

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本文介绍了一个使用MyBatis进行复杂关联映射的例子，包括一对一、一对多及多对多关系的处理方式。具体涉及表结构设计、Java对象模型定义、SQL查询语句与映射文件配置等内容。

1.表结构

CREATE TABLE `a` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(255) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=utf8;

CREATE TABLE `b` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(255) DEFAULT NULL,
  `aid` int(11) DEFAULT NULL,
  `c1` int(11) DEFAULT NULL,
  `c2` int(11) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8;

CREATE TABLE `c` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(255) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8;

2.对象

package com.testmybatis.model;

import java.util.List;

public class A {
	int id;
	String name;
	
	private List<B> blist;
	

	public List<B> getBlist() {
		return blist;
	}

	public void setBlist(List<B> blist) {
		this.blist = blist;
	}

	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;
	}

}

package com.testmybatis.model;

public class B {
	private int id;
	private String name;
	private int aid;
	private int c1;
	private int c2;
	
	private C c1obj;
	private C c2obj;
	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 int getAid() {
		return aid;
	}
	public void setAid(int aid) {
		this.aid = aid;
	}
	public int getC1() {
		return c1;
	}
	public void setC1(int c1) {
		this.c1 = c1;
	}
	public int getC2() {
		return c2;
	}
	public void setC2(int c2) {
		this.c2 = c2;
	}
	public C getC1obj() {
		return c1obj;
	}
	public void setC1obj(C c1obj) {
		this.c1obj = c1obj;
	}
	public C getC2obj() {
		return c2obj;
	}
	public void setC2obj(C c2obj) {
		this.c2obj = c2obj;
	}
	
	
}

3.collection

<select id="test" resultMap="aMap1">
		select 
			a.id as id,
			a.name as name,
			b.id as bid,
			b.name as bname,
			b.aid as aid,
			b.c1 as c1,
			b.c2 as c2
		from A a
		left join B b on a.id=b.aid
	</select>
	
    
    <resultMap type="com.testmybatis.model.A" id="aMap1">
        <id property="id" column="id"/> 
      	<result property="name" column="name"/>
        <collection property="blist" ofType="com.testmybatis.model.B">
            <id property="id" column="bid"/>
            <result property="name" column="bname"/>
            <result property="aid" column="aid"/>
            <result property="c1" column="c1"/>
            <result property="c2" column="c2"/>
        </collection>
    </resultMap>

4.association

<select id="testb" resultMap="aMap2">
		select 
			b.id as bid,
			b.name as bname,
			b.aid as aid,
			b.c1 as c1,
			b.c2 as c2,
			c1.id as c1id,
			c1.name as c1name,
			c2.id as c2id,
			c2.name as c2name 
		from B b
		left join C c1 on b.c1=c1.id
		left join C c2 on b.c2=c2.id 
	</select>
	
    
    <resultMap type="com.testmybatis.model.B" id="aMap2">
            <id property="id" column="bid"/>
            <result property="name" column="bname"/>
            <result property="aid" column="aid"/>
            <result property="c1" column="c1"/>
            <result property="c2" column="c2"/>
            <association property="c1obj" javaType="com.testmybatis.model.C" >
            	<id property="id" column="c1id"/>
            	<result property="name" column="c1name"/>
            </association>
            <association property="c2obj" javaType="com.testmybatis.model.C" >
            	<id property="id" column="c2id"/>
            	<result property="name" column="c2name"/>
            </association>
    </resultMap>

5. collection和association嵌套

<select id="test" resultMap="aMap">
		select 
			a.*,
			b.id bid,b.name bname,
			c1.id c1id,c1.name c1name,
			c2.id c2id,c2.name c2name 
		from A a
		left join B b on a.id=b.aid
		left join C c1 on b.c1=c1.id
		left join C c2 on b.c2=c2.id 
	</select>
	
	
	<resultMap type="com.testmybatis.model.A" id="aMap">
        <id property="id" column="id"/> 
      	<result property="name" column="name"/>
        <collection property="blist" ofType="com.testmybatis.model.B">
            <id property="id" column="bid"/>
            <result property="name" column="bname"/>
            
            <association property="c1obj" javaType="com.testmybatis.model.C" >
            	<id property="id" column="c1id"/>
            	<result property="name" column="c1name"/>
            </association>
            
            <association property="c2obj" javaType="com.testmybatis.model.C" >
            	<id property="id" column="c2id"/>
            	<result property="name" column="c2name"/>
            </association>
            
        </collection>
    </resultMap>