Mybatis Plus为我们提供了如下的一些条件构造器,我们可以利用它们实现查询条件、删除条件、更新条件的构造。
条件构造器用于给如下的Mapper方法传参,通常情况下:
public interface BaseMapper<T> extends Mapper<T> {
int delete(@Param("ew") Wrapper<T> wrapper);
int update(@Param("et") T entity, @Param("ew") Wrapper<T> updateWrapper);
T selectOne(@Param("ew") Wrapper<T> queryWrapper);
Integer selectCount(@Param("ew") Wrapper<T> queryWrapper);
List<T> selectList(@Param("ew") Wrapper<T> queryWrapper);
List<Map<String, Object>> selectMaps(@Param("ew") Wrapper<T> queryWrapper);
List<Object> selectObjs(@Param("ew") Wrapper<T> queryWrapper);
IPage<T> selectPage(IPage<T> page, @Param("ew") Wrapper<T> queryWrapper);
IPage<Map<String, Object>> selectMapsPage(IPage<T> page, @Param("ew") Wrapper<T> queryWrapper);
}
String name = "字母"; //name不为空
String email = ""; //email为空串
QueryWrapper<User> query = new QueryWrapper<>();
query.like(StringUtils.isNotEmpty(name), "name", name)
//因为email为空串,该条件未生效
.like(StringUtils.isNotEmpty(email), "email", email);
List<User> list = userMapper.selectList(query);
list.forEach(System.out::println);
email=“”
,所以.like(StringUtils.isNotEmpty(email), "email", email);
的条件不成立。
//构造条件
QueryWrapper<User> query = new QueryWrapper<>();
Map<String, Object> params = new HashMap<>();
params.put("name", "字母哥");
params.put("age", 18);
params.put("email", null);
// query.allEq(params,false);
query.allEq((k, v) -> !k.equals("name"), params, false);
List<User> list = userMapper.selectList(query);
list.forEach(System.out::println);
params.put("name", "字母哥");
这个查询条件被过滤掉params.put("email", null);
这个查询条件被过滤掉最终执行的SQL如下:
SELECT id,name,age,email,create_time
FROM user
WHERE age = ?
请参考:官方文档:条件构造器
// LambdaQueryWrapper<User> lambdaQ = new QueryWrapper<User>().lambda();
// LambdaQueryWrapper<User> lambdaQ = new LambdaQueryWrapper<>();
LambdaQueryWrapper<User> lambdaQ = Wrappers.lambdaQuery();
lambdaQ.like(User::getName, "字母")
.lt(User::getAge, 18);
List<User> list = userMapper.selectList(lambdaQ);
lambda条件构造器,最终执行SQL如下:
SELECT id,name,age,email,create_time
FROM user
WHERE name LIKE %字母%
AND age < 18
List<User> list = new LambdaQueryChainWrapper<User>(userMapper)
.likeRight(User::getName, "字母")
.and(q -> q.lt(User::getAge, 40)
.or()
.isNotNull(User::getEmail)
)
.list();
list.forEach(System.out::println);
lambda条件构造器,最终执行SQL如下:
SELECT id,name,age,email,create_time
FROM user
WHERE name LIKE '字母%'
AND ( age < 18 OR email IS NOT NULL )
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