【 MyBatis-Plus | 精讲 】

<dependency>
    <groupId>com.baomidou</groupId>
    <artifactId>mybatis-plus-boot-starter</artifactId>
    <version>3.5.3.1</version>
</dependency>

package com.itzhanghada.mp.mapper;

import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import com.itzhanghada.mp.domain.po.User;

public interface UserMapper extends BaseMapper<User> {
}

@TableName("user")
public class User {
    private Long id;
    private String name;
}

@TableName("user")
public class User {
    @TableId
    private Long id;
    private String name;
}

@TableName("user")
public class User {
    @TableId
    private Long id;
    private String name;
    private Integer age;
    @TableField(is_married")
    private Boolean isMarried;
    @TableField("`concat`")
    private String concat;
}

mybatis-plus:
  type-aliases-package: com.itzhanghada.mp.domain.po
  global-config:
    db-config:
      id-type: auto # 全局id类型为自增长

@Test
void testQueryWrapper() {
    // 1.构建查询条件 where name like "%o%" AND balance >= 1000
    QueryWrapper<User> wrapper = new QueryWrapper<User>()
            .select("id", "username", "info", "balance")
            .like("username", "o")
            .ge("balance", 1000);
    // 2.查询数据
    List<User> users = userMapper.selectList(wrapper);
    users.forEach(System.out::println);
}

@Test
void testUpdateByQueryWrapper() {
    // 1.构建查询条件 where name = "Jack"
    QueryWrapper<User> wrapper = new QueryWrapper<User>().eq("username", "Jack");
    // 2.更新数据，user中非null字段都会作为set语句
    User user = new User();
    user.setBalance(2000);
    userMapper.update(user, wrapper);
}

@Test
void testUpdateWrapper() {
    List<Long> ids = List.of(1L, 2L, 4L);
    // 1.生成SQL
    UpdateWrapper<User> wrapper = new UpdateWrapper<User>()
            .setSql("balance = balance - 200") // SET balance = balance - 200
            .in("id", ids); // WHERE id in (1, 2, 4)
        // 2.更新，注意第一个参数可以给null，也就是不填更新字段和数据，
    // 而是基于UpdateWrapper中的setSQL来更新
    userMapper.update(null, wrapper);
}

@Test
void testLambdaQueryWrapper() {
    // 1.构建条件 WHERE username LIKE "%o%" AND balance >= 1000
    LambdaQueryWrapper<User> wrapper = new LambdaQueryWrapper<>();
    wrapper
           .select(User::getId, User::getUsername, User::getInfo, User::getBalance)
           .like(User::getUsername, "o")
           .ge(User::getBalance, 1000);
    // 2.查询
    List<User> users = userMapper.selectList(wrapper);
    users.forEach(System.out::println);
}

mybatis-plus:
  global-config:
    db-config:
      logic-delete-field: deleted # 全局逻辑删除的实体字段名(since 3.3.0,配置后可以忽略不配置步骤2)
      logic-delete-value: 1 # 逻辑已删除值(默认为 1)
      logic-not-delete-value: 0 # 逻辑未删除值(默认为 0)

mybatis-plus:
  configuration:
    default-enum-type-handler: com.baomidou.mybatisplus.core.handlers.MybatisEnumTypeHandler

package com.itzhanghada.mp.enums;

import com.baomidou.mybatisplus.annotation.EnumValue;
import lombok.Getter;

@Getter
public enum UserStatus {
    NORMAL(1, "正常"),
    FREEZE(2, "冻结")
    ;
    @EnumValue
    private final int value;
    private final String desc;

    UserStatus(int value, String desc) {
        this.value = value;
        this.desc = desc;
    }
}

@Configuration​
public class MybatisConfig {​
​
    @Bean​
    public MybatisPlusInterceptor mybatisPlusInterceptor() {​
        // 初始化核心插件​
        MybatisPlusInterceptor interceptor = new MybatisPlusInterceptor();​
        // 添加分页插件​
        interceptor.addInnerInterceptor(new PaginationInnerInterceptor(DbType.MYSQL));​
        return interceptor;​
    }​
}

@Test
void testPageQuery() {
    // 1.分页查询，new Page()的两个参数分别是：页码、每页大小
    Page<User> p = userService.page(new Page<>(2, 2));
    // 2.总条数
    System.out.println("total = " + p.getTotal());
    // 3.总页数
    System.out.println("pages = " + p.getPages());
    // 4.数据
    List<User> records = p.getRecords();
    records.forEach(System.out::println);
}

int pageNo = 1, pageSize = 5;
// 分页参数
Page<User> page = Page.of(pageNo, pageSize);
// 排序参数, 通过OrderItem来指定
page.addOrder(new OrderItem("balance", false));

userService.page(page);

@Data​
public class PageQuery {​
    private Integer pageNo;​
    private Integer pageSize;​
    private String sortBy;​
    private Boolean isAsc;​
​
    public <T>  Page<T> toMpPage(OrderItem ... orders){​
        // 1.分页条件​
        Page<T> p = Page.of(pageNo, pageSize);​
        // 2.排序条件​
        // 2.1.先看前端有没有传排序字段​
        if (sortBy != null) {​
            p.addOrder(new OrderItem(sortBy, isAsc));​
            return p;​
        }​
        // 2.2.再看有没有手动指定排序字段​
        if(orders != null){​
            p.addOrder(orders);​
        }​
        return p;​
    }​
​
    public <T> Page<T> toMpPage(String defaultSortBy, boolean isAsc){​
        return this.toMpPage(new OrderItem(defaultSortBy, isAsc));​
    }​
​
    public <T> Page<T> toMpPageDefaultSortByCreateTimeDesc() {​
        return toMpPage("create_time", false);​
    }​
​
    public <T> Page<T> toMpPageDefaultSortByUpdateTimeDesc() {​
        return toMpPage("update_time", false);​
    }​
}

@Data​
@NoArgsConstructor​
@AllArgsConstructor​
public class PageDTO<V> {​
    private Long total;​
    private Long pages;​
    private List<V> list;​
​
    /**​
     * 返回空分页结果​
     * @param p MybatisPlus的分页结果​
     * @param <V> 目标VO类型​
     * @param <P> 原始PO类型​
     * @return VO的分页对象​
     */​
    public static <V, P> PageDTO<V> empty(Page<P> p){​
        return new PageDTO<>(p.getTotal(), p.getPages(), Collections.emptyList());​
    }​
​
    /**​
     * 将MybatisPlus分页结果转为 VO分页结果​
     * @param p MybatisPlus的分页结果​
     * @param voClass 目标VO类型的字节码​
     * @param <V> 目标VO类型​
     * @param <P> 原始PO类型​
     * @return VO的分页对象​
     */​
    public static <V, P> PageDTO<V> of(Page<P> p, Class<V> voClass) {​
        // 1.非空校验​
        List<P> records = p.getRecords();​
        if (records == null || records.size() <= 0) {​
            // 无数据，返回空结果​
            return empty(p);​
        }​
        // 2.数据转换​
        List<V> vos = BeanUtil.copyToList(records, voClass);​
        // 3.封装返回​
        return new PageDTO<>(p.getTotal(), p.getPages(), vos);​
    }​
​
    /**​
     * 将MybatisPlus分页结果转为 VO分页结果，允许用户自定义PO到VO的转换方式​
     * @param p MybatisPlus的分页结果​
     * @param convertor PO到VO的转换函数​
     * @param <V> 目标VO类型​
     * @param <P> 原始PO类型​
     * @return VO的分页对象​
     */​
    public static <V, P> PageDTO<V> of(Page<P> p, Function<P, V> convertor) {​
        // 1.非空校验​
        List<P> records = p.getRecords();​
        if (records == null || records.size() <= 0) {​
            // 无数据，返回空结果​
            return empty(p);​
        }​
        // 2.数据转换​
        List<V> vos = records.stream().map(convertor).collect(Collectors.toList());​
        // 3.封装返回​
        return new PageDTO<>(p.getTotal(), p.getPages(), vos);​
    }​
}