动态sql
if 标签
<!-- 演示动态sql-if标签的使用情景 -->
<select id="getUserByWhere" parameterType="user" resultType="com.itheima.mybatis.pojo.User">
<!-- SELECT * FROM USER WHERE username LIKE '%${username}%' and id = #{id} -->
SELECT * FROM USER where 1 = 1
<!-- if标签的使用 -->
<if test="id != null">
and id = #{id}
</if>
<if test="username != null and username != ''">
and username LIKE '%${username}%'
</if>
</select>
Where 标签
<!-- 演示动态sql-where标签的使用情景 -->
<select id="getUserByWhere2" parameterType="user"
resultType="com.itheima.mybatis.pojo.User">
<!-- include:引入sql片段,refid引入片段id -->
SELECT
*
FROM USER
<!-- where会自动加上where同处理多余的and -->
<where>
<!-- if标签的使用 -->
<if test="id != null">
and id = #{id}
</if>
<if test="username != null and username != ''">
and username LIKE '%${username}%'
</if>
</where>
</select>
foreach 标签
<!-- 演示动态sql-foreach标签的使用情景 -->
<select id="getUserByIds" parameterType="queryvo"
resultType="com.itheima.mybatis.pojo.User">
SELECT
*
FROM USER
<!-- where会自动加上where同处理多余的and -->
<where>
<!-- id IN(1,10,25,30,34) -->
<!-- foreach循环标签
collection:要遍历的集合,来源入参
open:循环开始前的sql
separator:分隔符
close:循环结束拼接的sql
-->
<foreach item="uid" collection="ids" open="id IN(" separator=","
close=")">
#{uid}
</foreach> </where>
</select>
Sql 片段
定义一个SQL片段
<!-- sql片段 定义,id:片段唯一标识 -->
<sql id="user_column">
`id`,
`username`,
`birthday`,
`sex`,
`address`,
`uuid2`
</sql>
使用SQL片段
SELECT
<!-- sql片段的使用:include:引入sql片段,refid引入片段id -->
<include refid="user_column" />
FROM USER
关联查询
一对一关联
- 方法一,使用resultType
- 新建OrderUser的pojo,继承自Order。
public class OrderUser extends Order {
private String username;
private String address;
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
public String getAddress() {
return address;
}
public void setAddress(String address) {
this.address= address;
}
}
新增查询方法getOrderUser。
<!-- 一对一关联查询,使用resultType -->
<select id="getOrderUser" resultType="orderuser">
SELECT
o.`id`,
o.`user_id` userId,
o.`number`,
o.`createtime`,
o.`note`,
u.`username`,
u.`address`
FROM `order` o
LEFT JOIN `user` u
ON u.id = o.`user_id`
</select>
- 方法二,使用resultMap
改造order的pojo
修改order的映射文件
<!-- 一对一关联查询-resultMap -->
<resultMap type="order" id="order_user_map">
<!-- id标签用于绑定主键 -->
<id property="id" column="id"/>
<!-- 使用result绑定普通字段 -->
<result property="userId" column="user_id"/>
<result property="number" column="number"/>
<result property="createtime" column="createtime"/>
<result property="note" column="note"/>
<!-- association:配置一对一关联
property:绑定的用户属性
javaType:属性数据类型,支持别名
-->
<association property="user" javaType="com.itheima.mybatis.pojo.User">
<id property="id" column="user_id"/>
<result property="username" column="username"/>
<result property="address" column="address"/>
<result property="sex" column="sex"/>
</association>
</resultMap>
<!-- 一对一关联查询-使用resultMap -->
<select id="getOrderUser2" resultMap="order_user_map">
SELECT
o.`id`,
o.`user_id`,
o.`number`,
o.`createtime`,
o.`note`,
u.`username`,
u.`address`,
u.`sex`
FROM `order` o
LEFT JOIN `user` u
ON u.id = o.`user_id`
</select>
一对多关联
- 改造user的pojo
修改user的映射文件
<!-- 一对多关联查询 -->
<resultMap type="user" id="user_order_map">
<id property="id" column="id" />
<result property="username" column="username" />
<result property="birthday" column="birthday" />
<result property="address" column="address" />
<result property="sex" column="sex" />
<result property="uuid2" column="uuid2" />
<!-- collection:配置一对多关系
property:用户下的order属性
ofType:property的数据类型,支持别名
-->
<collection property="orders" ofType="order">
<!-- id标签用于绑定主键 -->
<id property="id" column="oid"/>
<!-- 使用result绑定普通字段 -->
<result property="userId" column="id"/>
<result property="number" column="number"/>
<result property="createtime" column="createtime"/>
</collection>
</resultMap>
<!-- 一对多关联查询 -->
<select id="getUserOrder" resultMap="user_order_map">
SELECT
u.`id`,
u.`username`,
u.`birthday`,
u.`sex`,
u.`address`,
u.`uuid2`,
o.`id` oid,
o.`number`,
o.`createtime`
FROM `user` u
LEFT JOIN `order` o
ON o.`user_id` = u.`id`
</select>