mybatis中一对一关系映射

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>

原文地址：https://www.cnblogs.com/Magic-Li/p/11688270.html