ew是mapper方法里的@Param(Constants.WRAPPER) Wrapper queryWrapper对象
首先判断ew.emptyOfWhere是否存在where条件，有的话再拼接上去，ew.customSqlSegment是WHERE + sql语句
没有where的时候加上 == false
使用${ew.sqlSegment} 如果是连表查询且查询条件是连表的字段则需在service层拼接查询条件时字段前指定别名
最佳例子1
mapper.xml
<select id="tableList" resultType="java.util.LinkedHashMap">
SELECT
${ew.sqlSelect} // 这里拼接select后面的语句
FROM
${table_name} //如果是单表的话，这里可以写死
${ew.customSqlSegment}
</select>
mapper
IPage<LinkedHashMap<String,Object>> tableList(@Param("table_name") String table_name,
Page page,
@Param(Constants.WRAPPER) QueryWrapper queryWrapper);
test
String responseField = "*"; queryWrapper.select(responseField); // 即 select * ... String responseField = "name"; queryWrapper.select(responseField); // 即 select name ...
最佳例子2
controller
public String saveAddress(HttpSession session) {
UserVO user1 = (UserVO)session.getAttribute("user");
LambdaQueryWrapper<User> lambdaQueryWrapper = Wrappers.<User>lambdaQuery()
.select(User::getNickName, User::getUserId) // 需要查询的列，即 ${ew.sqlSelect}
.eq(User::getUserId, user1.getUserId());// 条件
User user = this.userMapper.selectNickNameAndUserId(lambdaQueryWrapper);
System.out.println(user);
return null;
}
mapper
User selectNickNameAndUserId(@Param(Constants.WRAPPER) LambdaQueryWrapper<User> queryWrapper);
mapper.xml
<select id="selectNickNameAndUserId" resultType="com.example.demo.entity.User">
select
<if test="ew != null and ew.SqlSelect != null and ew.SqlSelect != ''">
${ew.SqlSelect}
</if>
from
user
where is_deleted != 1
<if test="ew != null">
<if test="ew.nonEmptyOfWhere">
AND
</if>
${ew.sqlSegment}
</if>
</select>
<select id="selectNickNameAndUserId" resultType="com.example.demo.entity.User">
select
<if test="ew != null and ew.SqlSelect != null and ew.SqlSelect != ''">
${ew.SqlSelect}
</if>
from
user
${ew.customSqlSegment}
</select>
使用${ew.sqlSegment} 如果是联表查询且查询条件是连表的字段则需在service层拼接查询条件时字段前指定别名，而且不能用lambda的查询了
<select id="selectByRoleId" resultType="com.captain.crewer.mybatis.plus.dto.RolePermsDTO">
SELECT tp.id,
tp.perm_name,
tp.url,
tr.role_id as roleId,
tr.role_name as roleName
FROM tb_role tr
LEFT JOIN tb_perm_role tpr ON tr.role_id = tpr.role_id
LEFT JOIN tb_perm tp ON tpr.perm_id = tp.id ${ew.customSqlSegment}
</select>
mapper
List<RolePermsDTO> selectByRoleId(@Param(Constants.WRAPPER) Wrapper<RolePermsDTO> wrapper);
@Test
public void test2(){
QueryWrapper<RolePermsDTO> wrapper = new QueryWrapper<>();
wrapper.eq("tr.role_id", 1);
tbPermService.selectByRoleId(wrapper);
}