Preface
Lambda expressions are used. The entity field name operation can be used through method reference to avoid miswrite names when writing database table field names directly;
1. LambdaQueryWrapper<>
https:///program/
2. QueryWrapper<entity>().lambda()
/**
* The name is Wang's surname and (age less than 40 and the email address is not empty)
* name like 'king%' and (age <40 or email in not null)
* Generated sql statement SELECT id,name,age,email,manager_id,create_time FROM user WHERE name LIKE ? AND age < ?
*/
@Test
public void selectLambda2() {
LambdaQueryWrapper<User> lambda3 = Wrappers.<User>lambdaQuery();
(User::getName, "king").and(qw -> (User::getAge, 40).or().isNotNull(User::getEmail));
List<User> users = (lambda3);
(::println);
}
3. Wrappers.<entity>lambdaQuery()
/**
* lambda conditional constructor
* Generated sql statement SELECT id,name,age,email,manager_id,create_time FROM user WHERE name LIKE ? AND age < ?
*/
@Test
public void selectLambda() {
//Three ways to create a lambda conditional constructor// LambdaQueryWrapper<User> lambda2 = new LambdaQueryWrapper<>();
// LambdaQueryWrapper<User> lambda = new QueryWrapper<User>().lambda();
LambdaQueryWrapper<User> lambda3 = Wrappers.<User>lambdaQuery();
(User::getName, "rain").lt(User::getAge, 40);
List<User> users = (lambda3);
(::println);
}
/**
* The name is Wang's surname and (age less than 40 and the email address is not empty)
* name like 'king%' and (age <40 or email in not null)
* Generated sql statement SELECT id,name,age,email,manager_id,create_time FROM user WHERE name LIKE ? AND age < ?
*/
@Test
public void selectLambda2() {
LambdaQueryWrapper<User> lambda3 = Wrappers.<User>lambdaQuery();
(User::getName, "king").and(qw -> (User::getAge, 40).or().isNotNull(User::getEmail));
List<User> users = (lambda3);
(::println);
}
/**
* Custom SQL usage
* Dao layer code:
*
* @Select("select * from ${}")
* List<User> selectAll(@Param()Wrapper<User> wrapper);
*/
@Test
public void selectLambda4my() {
LambdaQueryWrapper<User> lambda3 = Wrappers.<User>lambdaQuery();
(User::getName, "king").and(qw -> (User::getAge, 40).or().isNotNull(User::getEmail));
List<User> users = (lambda3);
(::println);
}
Custom SQL in XML is just a single presentation here.
mybatis-plus: mapper-locations: - com/mp/mapper/*
UserMapper interface Add method
List<User> selectAll(@Param() Wrapper<User> wrapper);IPage<User> selectUserPage(Page<User> page,@Param()Wrapper<User> wrapper);
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper
PUBLIC "-////DTD Mapper 3.0//EN"
"/dtd/">
<mapper namespace="">
<select resultType="">
select * from user ${}
</select>
<select resultType="">
select * from user ${}
</select>
</mapper>
4. LambdaQueryChainWrapper<entity>(xxxxMapper)
/**
* The fourth way to create lambda conditional constructor MP 3.0.7 new method
* Generated sql statement SELECT id,name,age,email,manager_id,create_time FROM user WHERE name LIKE ? AND age >= ?
* This example shows that the code is more concise
* Generated sql statement SELECT id,name,age,email,manager_id,create_time FROM user WHERE name LIKE ? AND age >= ?
*/
@Test
public void selectLambda3() {
List<User> users = new LambdaQueryChainWrapper<User>(userMapper)
.like(User::getName, "rain").ge(User::getAge, 20).list();
(::println);
}
5. The application of lambda in pagination
MP pagination operation
The baseMapper interface provides two paging methods to implement physical paging (Note: the package that leads MP when leading packages) The first returns the entity object. Allows null. The second person returns the map object. It is mostly used when putting back a field, so as to avoid the null value of the specified field.
IPage<T> selectPage(IPage<T> page, @Param("ew") Wrapper<T> queryWrapper);
IPage<Map<String, Object>> selectMapsPage(IPage<T> page, @Param("ew") Wrapper<T> queryWrapper);
Pagination using MP requires configuration classes
package ;
import ;
import ;
import ;
@Configuration
public class MybatisPlusConfig {
@Bean
public PaginationInterceptor paginationInterceptor() {
return new PaginationInterceptor();
}
}
/**
* Pagination MP Pagination Plugin
*/
@Test
public void selectPage() {
QueryWrapper<User> queryWrapper = new QueryWrapper<User>();
("age", 26);
//The following parameter false indicates that the total number of records is not queried Page<User> userPage = new Page<>(1, 2, false);
/* IPage<User> iPage = (userPage, queryWrapper);
("Total Pages"+());
("Total record count"+());
List<User> records = ();
(::println);
*/
IPage<Map<String, Object>> iPage = (userPage, queryWrapper);
("Total Pages" + ());
("Total record count" + ());
List<Map<String, Object>> records = ();
(::println);
}
Custom paging
UserMapper interface
IPage<User> selectUserPage(Page<User> page,@Param()Wrapper<User> wrapper);
Add to
<select resultType="">
select * from user ${}
</select>
/**
* Custom paging method
*/
@Test
public void selectMyPage() {
QueryWrapper<User> queryWrapper = new QueryWrapper<User>();
("age", 26);
//The following parameter false indicates that the total number of records is not queried Page<User> page = new Page<>(1, 2);
IPage<User> iPage = (page, queryWrapper);
("Total Pages" + ());
("Total record count" + ());
List<User> records = ();
(::println);
}
This is the end of this article about implementing four lambda expressions in mybatis-plus. For more related content of mybatisplus lambda expressions, please search for my previous articles or continue browsing the related articles below. I hope everyone will support me in the future!