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>