你還在手寫(xiě) join 聯(lián)表查詢？MyBatis-Plus 這樣寫(xiě)太香了！
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使用方法
安裝
Maven
<dependency>
<groupId>com.github.yulichang</groupId>
<artifactId>mybatis-plus-join</artifactId>
<version>1.2.4</version>
</dependency>
Gradle
implementation 'com.github.yulichang:mybatis-plus-join:1.2.4'
或者clone代碼到本地執(zhí)行 mvn install, 再引入以上依賴
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使用
mapper繼承MPJBaseMapper (必選) service繼承MPJBaseService (可選) serviceImpl繼承MPJBaseServiceImpl (可選)
核心類 MPJLambdaWrapper和MPJQueryWrapper
MPJLambdaWrapper用法
簡(jiǎn)單的三表查詢
class test {
@Resource
private UserMapper userMapper;
void testJoin() {
List<UserDTO> list = userMapper.selectJoinList(UserDTO.class,
new MPJLambdaWrapper<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(UserDO::getId, 1)
.like(UserAddressDO::getTel, "1")
.gt(UserDO::getId, 5));
}
}
對(duì)應(yīng)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(shuō)明:
UserDTO.class 查詢結(jié)果返回類(resultType) selectAll() 查詢指定實(shí)體類的全部字段 select() 查詢指定的字段,支持可變參數(shù),同一個(gè)select只能查詢相同表的字段 故將UserAddressDO和AreaDO分開(kāi)為兩個(gè)select() selectAs() 字段別名查詢,用于數(shù)據(jù)庫(kù)字段與業(yè)務(wù)實(shí)體類屬性名不一致時(shí)使用 leftJoin() 參數(shù)說(shuō)明 第一個(gè)參數(shù): 參與連表的實(shí)體類class 第二個(gè)參數(shù): 連表的ON字段,這個(gè)屬性必須是第一個(gè)參數(shù)實(shí)體類的屬性 第三個(gè)參數(shù): 參與連表的ON的另一個(gè)實(shí)體類屬性 默認(rèn)主表別名是t,其他的表別名以先后調(diào)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(diào)用mp原生的方法,正常使用沒(méi)有sql注入風(fēng)險(xiǎn)
分頁(yè)查詢
class test {
@Resource
private UserMapper userMapper;
void testJoin() {
IPage<UserDTO> iPage = userMapper.selectJoinPage(new Page<>(2, 10), UserDTO.class,
new MPJLambdaWrapper<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(duì)應(yīng)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 ?,?
MPJQueryWrapper
簡(jiǎn)單的3表查詢
class test {
@Resource
private UserMapper userMapper;
void testJoin() {
List<UserDTO> list = userMapper.selectJoinList(UserDTO.class,
new MPJQueryWrapper<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")
.like("addr.tel", "1")
.le("a.province", "1"));
}
}
對(duì)應(yīng)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 (
addr.tel LIKE ?
AND a.province <= ?)
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說(shuō)明:
UserDTO.class 查詢結(jié)果類(resultType) selectAll(UserDO.class) 查詢主表全部字段(主表實(shí)體類)默認(rèn)主表別名 "t" select() mp的select策略是覆蓋,以最后一次為準(zhǔn),這里的策略是追加,可以一直select 主表字段可以用lambda,會(huì)自動(dòng)添加表別名,主表別名默認(rèn)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(guān)聯(lián)條件) 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(diào)用mp原生的方法,正常使用沒(méi)有sql注入風(fēng)險(xiǎn)
分頁(yè)查詢
class test {
@Resource
private UserMapper userMapper;
void testJoin() {
IPage<UserDTO> page = userMapper.selectJoinPage(new Page<>(1, 10), UserDTO.class,
new MPJQueryWrapper<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(duì)應(yīng)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 MPJQueryWrapper<UserDO>()
.selectAll(UserDO.class)
.select("addr.tel", "addr.address")
//行列轉(zhuǎn)換
.select("CASE t.sex WHEN '男' THEN '1' ELSE '0' END AS sex")
//求和函數(shù)
.select("sum(a.province) AS province")
//自定義數(shù)據(jù)集
.leftJoin("(select * from user_address) addr on t.id = addr.user_id")
.rightJoin("area a on addr.area_id = a.id")
.like("addr.tel", "1")
.le("a.province", "1")
.orderByDesc("addr.id"));
}
}
對(duì)應(yīng)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 (
addr.tel LIKE ?
AND a.province <= ?)
ORDER BY
addr.id DESC
作者：陽(yáng)宗德
鏈接：https://juejin.cn/post/7110405284811522085
End
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