mybatis中一对一关系映射
Posted Magic_Li
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一对一关系中普通的配置方式
一.多表连接查询语句:
<select id="selectStudentWithAddress" parameterType="int" resultMap="StudentWithAddressResult"> select s.stud_id, s.name, s.email,s.dob,s.phone, a.addr_id, a.street, a.city, a.state, a.zip,a.country from students s left outer join addresses a on s.addr_id=a.addr_id where stud_id=#{id} </select>
1. 把所有的查询结果,在一个resultMap中映射
<resultMap type="Student" id="StudentWithAddressResult"> <id property="studId" column="stud_id" /> <result property="name" column="name" /> <result property="email" column="email" /> <result property="phone" column="phone" /> <!--adderss是Student的内置对象--> <result property="address.addrId" column="addr_id" /> <result property="address.street" column="street" /> <result property="address.city" column="city" /> <result property="address.state" column="state" /> <result property="address.zip" column="zip" /> <result property="address.country" column="country" /> </resultMap>
2.使用【嵌套结果】ResultMap,实现一对一关系映射(就是说在一个resultMap中映射部分字段,在另一个映射结果中关联)
<resultMap type="Address" id="AddressResult"> <id property="addrId" column="addr_id" /> <result property="street" column="street" /> <result property="city" column="city" /> <result property="state" column="state" /> <result property="zip" column="zip" /> <result property="country" column="country" /> </resultMap>
注:<association>是关联的意思,常被用来表示(has-one)类型的关联。就是对象1里面关联另一个对象2
<resultMap type="Student" id="StudentWithAddressResult"> <id property="studId" column="stud_id" /> <result property="name" column="name" /> <result property="email" column="email" /> <result property="dob" column="dob" /> <result property="phone" column="phone" /> <association property="address" resultMap="AddressResult" /> </resultMap>
3.定义【内联】的resultMap
<resultMap type="Student" id="StudentWithAddressResult"> <id property="studId" column="stud_id" /> <result property="name" column="name" /> <result property="email" column="email" /> <association property="address" javaType="Address"> <id property="addrId" column="addr_id" /> <result property="street" column="street" /> <result property="city" column="city" /> <result property="state" column="state" /> <result property="zip" column="zip" /> <result property="country" column="country" /> </association> </resultMap>
二.嵌套查询语句select,实现一对一关系映射
在一个映射结果中,嵌套了另一个select语句
<resultMap type="Address" id="AddressResult"> <id property="addrId" column="addr_id" /> <result property="street" column="street" /> <result property="city" column="city" /> <result property="state" column="state" /> <result property="zip" column="zip" /> <result property="country" column="country" /> </resultMap>
独立的select查询,专门查询Address
<select id="findAddressById" parameterType="int" resultMap="AddressResult"> select * from addresses where addr_id=#{id} </select>
Student封装映射,里面关联了查询address使用的select语句,并指定数据库表中的这个关联的外键列的名字,这里是addr_id
<resultMap type="Student" id="StudentWithAddressResult"> <id property="studId" column="stud_id" /> <result property="name" column="name" /> <result property="email" column="email" /> <result property="dob" column="dob" /> <result property="phone" column="phone" /> <!--第一条sql语句查出的addr_id值当作参数传给findAddressById,然后封装个Address对象传给address--> <!--相当于将AddressResult结果集映射进来封装成一个Address类型的对象,传给Student类型中的address属性--> <!-- property="address" 这是类中的属性 将column="addr_id"的值传给select="findAddressById" 这个语句,返回address对应的结果集--> <association property="address" column="addr_id" select="findAddressById" /> </resultMap>
查询Student的select语句,这里不用写多表查询,因为对于address的关联查询,已经在上边定义好了,并且在结果映射中关联进来了
<select id="selectStudentWithAddress" parameterType="int" resultMap="StudentWithAddressResult"> select * from students where stud_id=#{id} </select>
三.实现插入功能,要注意ADDRESSES表中的ADDR_ID字段在STUDENTS表中做主键
<insert id="insertStudent" parameterType="Student"> <selectKey keyProperty="studId" resultType="int" order="BEFORE"> select my_seq.nextval from dual </selectKey> INSERT INTO STUDENTS(STUD_ID,NAME,EMAIL,DOB,PHONE,ADDR_ID) <!-- 这里注意,使用以下的顺序调用,才可以使最后的ADDR_ID有值--> <!-- mapper.insertAddress(address); <!--在这里调用这个方法后address对象就会利用序列自动生成主键addrId,并且保存到address对象中--> mapper.insertStudent(stu); sqlSession.commit(); --> VALUES(#{studId},#{name},#{email},#{dob},#{phone},#{address.addrId}) <!-- 如果是对象自己取自己的值用作插入或判断条件,不可以写#{this.属性} 应当直接写#{属性} --> </insert> <insert id="insertAddress" parameterType="Address"> <selectKey keyProperty="addrId" resultType="int" order="BEFORE"> select my_seq.nextval from dual </selectKey> INSERT INTO ADDRESSES(ADDR_ID,STREET,CITY,STATE,ZIP,COUNTRY) VALUES(#{addrId},#{street},#{city},#{state},#{zip},#{country}) </insert>
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