association：用於物件間包含關係對映
方式一：通過association標籤來封裝結果集
<namespace
>
<
resultmap
type
="org.apache.ibatis.submitted.associationtest.car"
id="carresult"
>
<
id column
="carid"
property
="id"
/>
<
result
column
="cartype"
property
="type"
/>
<
association
property
="engine"
resultmap
="engineresult"
/>
<
association
property
="brakes"
resultmap
="brakesresult"
/>
resultmap
>
<
resultmap
type
="org.apache.ibatis.submitted.associationtest.engine"
id="engineresult"
>
<
result
column
="enginetype"
property
="type"
/>
<
result
column
="enginecylinders"
property
="cylinders"
/>
resultmap
>
<
resultmap
type
="org.apache.ibatis.submitted.associationtest.brakes"
id="brakesresult"
>
<
result
column
="brakestype"
property
="type"
/>
resultmap
>
<
select
id="getcars"
resultmap
="carresult"
>
select * from cars
select
>
<
select
id="getcarsnonunique"
resultmap
="carresult"
>
select 1 as carid, cartype, enginetype, enginecylinders, brakestype from cars
select
>
<
select
id="getcars2"
resultmap
="carresult"
>
select 1 as carid, cartype, enginetype, enginecylinders, brakestype from cars where carid in (1,2)
select
>
>
查詢：
<select id="getempanddept" resultmap="complexemp2">
select e.id id,e.last_name last_name,e.email email,e.gender gender,e.d_id d_id,d.id did,d.dept_name dept_name from tb1_emplyee e,tb1_dept d where e.d_id=d.id and e.id=
#select
>
方式二：通過association標籤實現分段查詢
<resultmap
id="myempbystep"
type
="com.test.beans.employee"
>
<
id column
="id"
property
="id"
/>
<
result
column
="last_name"
property
="lastname"
/>
<
result
column
="email"
property
="email"
/>
<
result
column
="gender"
property
="gender"
/>
<
association
property
="dept"
select
column
="d_id"
>
association
>
resultmap
>
對應的department對映檔案:
<namespace
>
<
select
id="getdeptbyid"
resulttype
="com.test.beans.department"
>
select id,dept_name departmentname from tb1_dept where id=#
select
>
>
查詢：
<select
id="getempbyidstep"
resultmap
="myempbystep"
>
select * from tb1_emplyee where id=#
select
>
association標籤還可以實現懶載入的功能
什麼是懶載入呢?
前面的分步查詢,每查詢一次都會執行兩次sql(一次查詢員工,一次查詢部門)
有時候我們並不需要插敘部門的情況,所以懶查詢就可以幫我們解決這個問題,提高效率,減少資源的占用
懶載入的實現也非常簡單,只要在全域性配置檔案中新增如下的配置**即可:
<settings
>
<
setting
name
="lazyloadingenabled"
value
="true"
/>
<
setting
name
="aggressivelazyloading"
value
="false"
/>
settings
>
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