MyBatis-Plus 如何實現連表查詢
安裝
-
在項目中添加依賴,依賴已經包含了mybatis-plus-boot-starter<3.4.2>
依賴后無需再次引入mybatis-plus<dependency> <groupId>com.github.yulichang</groupId> <artifactId>mybatis-plus-join</artifactId> <version>1.0.8</version> </dependency>或者clone代碼到本地,執行mvn install,再引入以上依賴
-
配置插件,添加MPJInterceptor
@Configuration public class MybatisPlusConfig { /** * 啟用連表攔截器 */ @Bean public MybatisPlusInterceptor paginationInterceptor() { MybatisPlusInterceptor interceptor = new MybatisPlusInterceptor(); //分頁插件 interceptor.addInnerInterceptor(new PaginationInnerInterceptor()); //連表插件 interceptor.addInnerInterceptor(new MPJInterceptor()); //多租戶,垃圾sql攔截插件...... return interceptor; } }
使用
- mapper繼承MPJBaseMapper (必選)
- service繼承MPJBaseService (可選)
- serviceImpl繼承MPJBaseServiceImpl (可選)
-
MPJBaseMapper繼承BaseMapper,在原有的方法基礎上又添加了以下方法
-
MPJBaseService 繼承了IService,同樣添加以上方法
-
MPJBaseServiceImpl 繼承了ServiceImpl,同樣添加了以上方法
簡單的3表查詢
class test {
@Resource
private UserMapper userMapper;
void testJoin() {
List<UserDTO> list = userMapper.selectJoinList(UserDTO.class,
new MPJLambdaQueryWrapper<UserDO>()
.selectAll(UserDO.class)
.select("addr.tel", "addr.address", "a.province")
.leftJoin("user_address addr on t.id = addr.user_id")
.rightJoin("area a on addr.area_id = a.id")
.gt(true, UserDO::getId, 1)
.eq(true, UserDO::getSex, "男")
.stringQuery()
.like(true, "addr.tel", "1")
.le(true, "a.province", "1"));
}
}
對應sql
SELECT
t.id,
t.name,
t.sex,
t.head_img,
addr.tel,
addr.address,
a.province
FROM
user t
LEFT JOIN user_address addr on t.id = addr.user_id
RIGHT JOIN area a on addr.area_id = a.id
WHERE (
t.id > ?
AND t.sex = ?
AND addr.tel LIKE ?
AND a.province <= ?)
說明:
- UserDTO.class 查詢結果類(resultType)
- selectAll(UserDO.class) 查詢主表全部字段(主表實體類)
- select() mp的select策略是覆蓋,以最后一次為准,這里的策略是追加,可以一直select
主表字段可以用lambda,會自動添加表別名,主表別名默認是 t ,非主表字段必須帶別名查詢 - leftJoin() rightJoin() innerJoin() 傳sql片段 格式 (表 + 別名 + 關聯條件)
- stringQuery() lambda查詢轉string查詢
- lambda() string查詢轉lambda查詢
- 條件查詢,可以查詢主表以及參與連接的所有表的字段,全部調用mp原生的方法,正常使用沒有sql注入風險
分頁查詢
class test {
@Resource
private UserMapper userMapper;
void testJoin() {
IPage<UserDTO> page = userMapper.selectJoinPage(new Page<>(1, 10), UserDTO.class,
new MPJLambdaQueryWrapper<UserDO>()
.selectAll(UserDO.class)
.select("addr.tel", "addr.address")
.select("a.province")
.leftJoin("user_address addr on t.id = addr.user_id")
.rightJoin("area a on addr.area_id = a.id"));
}
}
對應sql
SELECT
t.id,
t.name,
t.sex,
t.head_img,
addr.tel,
addr.address,
a.province
FROM
user t
LEFT JOIN user_address addr on t.id = addr.user_id
RIGHT JOIN area a on addr.area_id = a.id
LIMIT ?,?
還可以這么操作,但不建議
class test {
@Resource
private UserMapper userMapper;
void testJoin() {
List<UserDTO> list = userMapper.selectJoinList(UserDTO.class,
new MPJLambdaQueryWrapper<UserDO>()
.selectAll(UserDO.class)
.select("addr.tel", "addr.address")
//行列轉換
.select("CASE t.sex WHEN '男' THEN '1' ELSE '0' END AS sex")
//求和函數
.select("sum(a.province) AS province")
//自定義數據集
.leftJoin("(select * from user_address) addr on t.id = addr.user_id")
.rightJoin("area a on addr.area_id = a.id")
.eq(true, UserDO::getId, 1)
.stringQuery()
.like(true, "addr.tel", "1")
.le(true, "a.province", "1")
.orderByDesc("addr.id"));
}
}
對應sql
SELECT
t.id,
t.name,
t.sex,
t.head_img,
addr.tel,
addr.address,
CASE t.sex WHEN '男' THEN '1' ELSE '0' END AS sex,
sum(a.province) AS province
FROM
user t
LEFT JOIN (select * from user_address) addr on t.id = addr.user_id
RIGHT JOIN area a on addr.area_id = a.id
WHERE (
t.id = ?
AND addr.tel LIKE ?
AND a.province <= ?)
ORDER BY
addr.id DESC
騷操作
簡單的3表查詢
class test {
@Resource
private UserMapper userMapper;
void testJoin() {
List<UserDTO> list = userMapper.selectJoinList(UserDTO.class,
new MPJJoinLambdaQueryWrapper<UserDO>()
.selectAll(UserDO.class)
.select(UserAddressDO::getTel)
.selectAs(UserAddressDO::getAddress, UserDTO::getUserAddress)
.select(AreaDO::getProvince, AreaDO::getCity)
.leftJoin(UserAddressDO.class, UserAddressDO::getUserId, UserDO::getId)
.leftJoin(AreaDO.class, AreaDO::getId, UserAddressDO::getAreaId)
.eq(true, UserDO::getId, 1)
.like(true, UserAddressDO::getTel, "1")
.gt(true, UserDO::getId, 5));
}
}
對應sql
SELECT
t.id,
t.name,
t.sex,
t.head_img,
t1.tel,
t1.address AS userAddress,
t2.province,
t2.city
FROM
user t
LEFT JOIN user_address t1 ON t1.user_id = t.id
LEFT JOIN area t2 ON t2.id = t1.area_id
WHERE (
t.id = ?
AND t1.tel LIKE ?
AND t.id > ?)
說明:
- UserDTO.class 查詢結果返回類(resultType)
- selectAll() 查詢指定實體類的全部字段
- select() 查詢指定的字段,支持可變參數,同一個select只能查詢相同表的字段
故將UserAddressDO和AreaDO分開為兩個select() - selectAs() 字段別名查詢,用於數據庫字段與業務實體類屬性名不一致時使用
- leftJoin() 參數說明
第一個參數: 參與連表的實體類class
第二個參數: 連表的ON字段,這個屬性必須是第一個參數實體類的屬性
第三個參數: 參與連表的ON的另一個實體類屬性 - 默認主表別名是t,其他的表別名以先后調用的順序使用t1,t2,t3....
- 條件查詢,可以查詢主表以及參與連接的所有表的字段,全部調用mp原生的方法,正常使用沒有sql注入風險
分頁查詢
class test {
@Resource
private UserMapper userMapper;
void testJoin() {
IPage<UserDTO> iPage = userMapper.selectJoinPage(new Page<>(2, 10), UserDTO.class,
new MPJJoinLambdaQueryWrapper<UserDO>()
.selectAll(UserDO.class)
.select(UserAddressDO::getTel)
.selectAs(UserAddressDO::getAddress, UserDTO::getUserAddress)
.select(AreaDO::getProvince, AreaDO::getCity)
.leftJoin(UserAddressDO.class, UserAddressDO::getUserId, UserDO::getId)
.leftJoin(AreaDO.class, AreaDO::getId, UserAddressDO::getAreaId));
}
}
對應sql
SELECT
t.id,
t.name,
t.sex,
t.head_img,
t1.tel,
t1.address AS userAddress,
t2.province,
t2.city
FROM
user t
LEFT JOIN user_address t1 ON t1.user_id = t.id
LEFT JOIN area t2 ON t2.id = t1.area_id
LIMIT ?,?