mybatis-plus高級操作

lambda條件構造器 使用

 

  /**
     * lambda 條件構造器
     * 生成的sql語句 SELECT id,name,age,email,manager_id,create_time FROM user WHERE name LIKE ? AND age < ?
     */
    @Test
    public void selectLambda() {
        //創建lambda 條件構造器 的三種方法
//       LambdaQueryWrapper<User> lambda2 = new LambdaQueryWrapper<>();
// LambdaQueryWrapper<User> lambda = new QueryWrapper<User>().lambda();
 LambdaQueryWrapper<User> lambda3 = Wrappers.<User>lambdaQuery();
        lambda3.like(User::getName, "雨").lt(User::getAge, 40);
        List<User> users = userMapper.selectList(lambda3);
        users.forEach(System.out::println);


    }

/**
 * 名字為王姓並且（年齡小於40並且郵箱不為空）
 * name like '王%' and (age <40 or email in not null)
 * 生成的sql語句 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();
 lambda3.likeRight(User::getName, "王").and(qw -> qw.lt(User::getAge, 40).or().isNotNull(User::getEmail));

 List<User> users = userMapper.selectList(lambda3);
    users.forEach(System.out::println);


}

/**
 * 自定義sql 使用
 * Dao層  代碼：
 *
 * @Select("select * from ${ew.customSqlSegment}")
 * List<User> selectAll(@Param(Constants.WRAPPER)Wrapper<User> wrapper);
 */
@Test
public void selectLambda4my() {
    LambdaQueryWrapper<User> lambda3 = Wrappers.<User>lambdaQuery();
 lambda3.likeRight(User::getName, "王").and(qw -> qw.lt(User::getAge, 40).or().isNotNull(User::getEmail));

 List<User> users = userMapper.selectAll(lambda3);
    users.forEach(System.out::println);


}
xml方式自定義sql 這里只是個單表演示
application.yml 添加

mybatis-plus:
  mapper-locations:
    - com/mp/mapper/*
UserMapper 接口 添加方法

List<User> selectAll(@Param(Constants.WRAPPER) Wrapper<User> wrapper);

IPage<User> selectUserPage(Page<User> page,@Param(Constants.WRAPPER)Wrapper<User> wrapper);

UserMpper.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.mp.dao.UserMapper">
    <select id="selectAll" resultType="com.mp.entity.User">
        select * from user ${ew.customSqlSegment}
    </select>

    <select id="selectUserPage" resultType="com.mp.entity.User">
        select * from user ${ew.customSqlSegment}
    </select>
</mapper>

/**
 * lambda 條件構造器第四種創建方式 MP 3.0.7 新增的方式
 * 生成的sql語句 SELECT id,name,age,email,manager_id,create_time FROM user WHERE name LIKE ? AND age >= ?
 * 這個例子可以看出  代碼更簡潔了
 * 生成的sql語句 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, "雨").ge(User::getAge, 20).list();

    users.forEach(System.out::println);
}

MP的分頁操作
baseMapper接口提供兩種分頁方法來實現物理分頁（注：導包時導MP的包）
第一個返回實體對象 允許null 第二個人返回map 對象多用於在指定放回字段時使用，避免為指定字段null值出現

 IPage<T> selectPage(IPage<T> page, @Param("ew") Wrapper<T> queryWrapper);

    IPage<Map<String, Object>> selectMapsPage(IPage<T> page, @Param("ew") Wrapper<T> queryWrapper);


使用MP的分頁需要配置 類

package com.mp.configuration;

import com.baomidou.mybatisplus.extension.plugins.PaginationInterceptor;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class MybatisPlusConfig {


    @Bean
    public PaginationInterceptor paginationInterceptor() {
        return new PaginationInterceptor();
    }
}

/**
 * 分頁MP 分頁插件 
 */
@Test
public void selectPage() {
    QueryWrapper<User> queryWrapper = new QueryWrapper<User>();
    queryWrapper.ge("age", 26);
    //后面參數false  表示不查詢總記錄數
 Page<User> userPage = new Page<>(1, 2, false);
 /* IPage<User> iPage = userMapper.selectPage(userPage, queryWrapper);
    System.out.println("總頁數"+iPage.getPages());
    System.out.println("總記錄數"+iPage.getTotal());
    List<User> records = iPage.getRecords();
    records.forEach(System.out::println);
    */
 IPage<Map<String, Object>> iPage = userMapper.selectMapsPage(userPage, queryWrapper);
    System.out.println("總頁數" + iPage.getPages());
    System.out.println("總記錄數" + iPage.getTotal());
    List<Map<String, Object>> records = iPage.getRecords();

    records.forEach(System.out::println);

}

自定義分頁
UserMapper接口添加 xml方式和注解方式sql是相同的 上面有示例

IPage<User> selectUserPage(Page<User> page,@Param(Constants.WRAPPER)Wrapper<User> wrapper);

UserMpper.xml 添加

<select id="selectUserPage" resultType="com.mp.entity.User">
    select * from user ${ew.customSqlSegment}
</select>

/**
 * 自定義分頁方法
 */
@Test
public void selectMyPage() {
    QueryWrapper<User> queryWrapper = new QueryWrapper<User>();
    queryWrapper.ge("age", 26);
    //后面參數false  表示不查詢總記錄數
    Page<User> page = new Page<>(1, 2);

    IPage<User> iPage = userMapper.selectUserPage(page, queryWrapper);
    System.out.println("總頁數" + iPage.getPages());
    System.out.println("總記錄數" + iPage.getTotal());
    List<User> records = iPage.getRecords();
    records.forEach(System.out::println);
}