mybatis级联查询

查询返回对象里面包含一个对象

<?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.bdm.mappers.EmpMapper">
	<resultMap id="EmpResultMap" type="com.bdm.entities.Emp">
		<id property="id" column="id" />
		<result property="name" column="name" />
		 
		<association property="dept" column="dept_id"
			select="com.bdm.mappers.DeptMapper.getById" />
	</resultMap>
	<select id="getById" parameterType="Integer" resultMap="EmpResultMap">
		select *
		from tbl_emp where id=#{id}
	</select>
</mapper>

<?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.bdm.mappers.DeptMapper">
	<resultMap id="DeptResultMap" type="com.bdm.entities.Dept">
		<id property="id" column="id" />
		<result property="name" column="name" />
		 
	</resultMap>
	<select id="getById" parameterType="Integer" resultMap="DeptResultMap">
		select id from tbl_dept where id = #{id}
	</select>
</mapper>

select="dao路径加方法接口名称"《》-----》对象接口路径下面的方法

column《------------------------》传参数的列名

如果多参数传参---------------------》{key=value,key2=value2}

parameterType：传参类型

查询返回对象里面包含一个对象集合（list）

<?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.bdm.mappers.DeptMapper">
	<resultMap id="DeptResultMap" type="com.bdm.entities.Dept">
		<id property="id" column="id" />
		<result property="deptName" column="dept_name" />
		
		<collection property="emps" column="id" ofType="com.bdm.entities.Emp"
			select="com.bdm.mappers.EmpMapper.getEmpByDeptId" />
	</resultMap>
	<select id="getById" parameterType="Integer" resultMap="DeptResultMap">
		select * from tbl_dept where id = #{id}
	</select>
</mapper>

property：对象里面的集合名称     ofType：实体对应路径

select: dao层路径加具体接口方法名称

column：传参

<?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.bdm.mappers.EmpMapper">
	<resultMap id="EmpResultMap" type="com.bdm.entities.Emp">
		<id property="id" column="id" />
		<result property="name" column="name" />
	</resultMap>
	<select id="getEmpByDeptId" parameterType="Integer" resultMap="EmpResultMap">
		select * from tbl_emp where dept_Id = #{deptId}
	</select>
</mapper>

注意懒加载：使用是才会出发具体的SQL字段或者SQL语句

按照实际情况自行配置

mybatis.configuration.lazy-loading-enabled=true
#false 为按需加载
mybatis.configuration.aggressive-lazy-loading=false
 

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