mybatis-plus高级操作

lambda条件构造器 使用

  /**
     * lambda 条件构造器
     * 生成的sql语句 SELECT id,name,age,email,manager_id,create_time FROM user WHERE name LIKE ? AND age < ?
     */
    @Test
    public void selectLambda() {
        //创建lambda 条件构造器 的三种方法
//        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);


    }

/**
 * 名字为王姓并且（年龄小于40并且邮箱不为空）
 * name like '王%' and (age <40 or email in not null)
 * 生成的sql语句 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);


}

/**
 * 自定义sql 使用
 * Dao层  代码：
 *
 * @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方式自定义sql 这里只是个单表演示
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 条件构造器第四种创建方式 MP 3.0.7 新增的方式
 * 生成的sql语句 SELECT id,name,age,email,manager_id,create_time FROM user WHERE name LIKE ? AND age >= ?
 * 这个例子可以看出  代码更简洁了
 * 生成的sql语句 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的分页操作
baseMapper接口提供两种分页方法来实现物理分页（注：导包时导MP的包）
第一个返回实体对象 允许null 第二个人返回map 对象多用于在指定放回字段时使用，避免为指定字段null值出现

 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的分页需要配置 类

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();
    }
}

/**
 * 分页MP 分页插件 
 */
@Test
public void selectPage() {
    QueryWrapper<User> queryWrapper = new QueryWrapper<User>();
    queryWrapper.ge("age", 26);
    //后面参数false  表示不查询总记录数
    Page<User> userPage = new Page<>(1, 2, false);
  /*  IPage<User> iPage = userMapper.selectPage(userPage, queryWrapper);
    System.out.println("总页数"+iPage.getPages());
    System.out.println("总记录数"+iPage.getTotal());
    List<User> records = iPage.getRecords();
    records.forEach(System.out::println);
    */
    IPage<Map<String, Object>> iPage = userMapper.selectMapsPage(userPage, queryWrapper);
    System.out.println("总页数" + iPage.getPages());
    System.out.println("总记录数" + iPage.getTotal());
    List<Map<String, Object>> records = iPage.getRecords();

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

}

自定义分页
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>

/**
 * 自定义分页方法
 */
@Test
public void selectMyPage() {
    QueryWrapper<User> queryWrapper = new QueryWrapper<User>();
    queryWrapper.ge("age", 26);
    //后面参数false  表示不查询总记录数
    Page<User> page = new Page<>(1, 2);

    IPage<User> iPage = userMapper.selectUserPage(page, queryWrapper);
    System.out.println("总页数" + iPage.getPages());
    System.out.println("总记录数" + iPage.getTotal());
    List<User> records = iPage.getRecords();
    records.forEach(System.out::println);
}