mybatis中一對一關係映射

一對一關係中普通的配置方式

一.多表連接查詢語句:

<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. 把所有的查詢結果，在一個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的內置對象-->
<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【嵌套結果】ResultMap，實現一對一關係映射(就是說在一個resultMap中映射部分欄位，在另一個映射結果中關聯)

<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>    

註:<association>是關聯的意思,常被用來表示(has-one)類型的關聯。就是對象1裡面關聯另一個對象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.定義【內聯】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.嵌套查詢語句select，實現一對一關係映射

在一個映射結果中，嵌套了另一個select語句 

<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>

獨立的select查詢，專門查詢Address

<select id="findAddressById" parameterType="int"
resultMap="AddressResult">
select * from addresses
where addr_id=#{id}
</select>

Student封裝映射，裡面關聯了查詢address使用的select語句，並指定資料庫表中的這個關聯的外鍵列的名字，這裡是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" />
<!--第一條sql語句查出的addr_id值當作參數傳給findAddressById，然後封裝個Address對象傳給address-->
<!--相當於將AddressResult結果集映射進來封裝成一個Address類型的對象,傳給Student類型中的address屬性-->
<!-- property="address" 這是類中的屬性 將column="addr_id"的值傳給select="findAddressById" 這個語句,返回address對應的結果集-->
<association property="address" column="addr_id"
select="findAddressById" />
</resultMap>

查詢Student的select語句，這裡不用寫多表查詢，因為對於address的關聯查詢，已經在上邊定義好了，並且在結果映射中關聯進來了

<select id="selectStudentWithAddress" parameterType="int"
resultMap="StudentWithAddressResult">
select * from students
where stud_id=#{id}
</select> 

三.實現插入功能，要註意ADDRESSES表中的ADDR_ID欄位在STUDENTS表中做主鍵

<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) 
<!-- 這裡註意，使用以下的順序調用，才可以使最後的ADDR_ID有值-->
<!-- mapper.insertAddress(address);
<!--在這裡調用這個方法後address對象就會利用序列自動生成主鍵addrId，並且保存到address對象中-->
mapper.insertStudent(stu);
sqlSession.commit(); 
-->
VALUES(#{studId},#{name},#{email},#{dob},#{phone},#{address.addrId})
<!-- 如果是對象自己取自己的值用作插入或判斷條件，不可以寫#{this.屬性} 應當直接寫#{屬性} -->
</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>