MyBatisPlus插件的学习1

简化开发, 活用插件. 拥抱变化,持续学习.

首先是配置1:

        <dependency>
            <groupId>com.baomidou</groupId>
            <artifactId>mybatis-plus-boot-starter</artifactId>
            <version>3.2.0</version>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
        </dependency>

配置2 :

server:
  port: 8008
  servlet:
    context-path: /mp
spring:
  datasource:
    username: root
    password: 123
    url: jdbc:mysql://127.0.0.1:3306/mp?serverTimezone=GMT%2B8&useUnicode=true&characterEncoding=utf-8
    driver-class-name: com.mysql.cj.jdbc.Driver
logging:
  level:
    root: warn
    com.example.demo.dao: trace
  pattern:
    console: '%p%m%n'
#xml自定义sql
mybatis-plus:
  mapper-locations:
  - com/example/demo/mapper/*

常用注解 @TableName 类名<===>表名

                @TableId  主键映射

                @TableField 列名映射    ps (驼峰命名对应_, managerId <==>  manager_id)

                    当 exist = false 数据不会插入数据库

来自BaseMapper常规API:

 /**
     * 插入一条记录
     *
     * @param entity 实体对象
     */
    int insert(T entity);

    /**
     * 根据 ID 删除
     *
     * @param id 主键ID
     */
    int deleteById(Serializable id);

    /**
     * 根据 columnMap 条件，删除记录
     *
     * @param columnMap 表字段 map 对象  (key数据库的列名,value比较的值)
     */
    int deleteByMap(@Param(Constants.COLUMN_MAP) Map<String, Object> columnMap);

    /**
     * 删除（根据ID 批量删除）
     *
     * @param idList 主键ID列表(不能为 null 以及 empty)
     */
    int deleteBatchIds(@Param(Constants.COLLECTION) Collection<? extends Serializable> idList);

条件构造器AbstractWrapper :

以查询方法举例子(构造实例):
QueryWrapper<User> query = Wrappers.query();
@Param(Constants.WRAPPER) Wrapper<T> queryWrapper
new LambdaQueryChainWrapper<>(userMapper)
LambdaQueryWrapper<User> query = Wrappers.lambdaQuery();

详细案例:

// WHERE (username LIKE ? AND age BETWEEN ? AND ? OR age >= ?) ORDER BY id DESC
        query.likeRight("username", "张").between("age", 20, 30).or().ge("age", 20).orderByDesc("id");
// 子查询,时间格式
// WHERE (date_format(create_time,'%Y-%m-%d') = ? AND manager_id IN (select id from mp_user where username like '大%'))
query.apply("date_format(create_time,'%Y-%m-%d') = {0}", "2019-09-28").inSql("manager_id","select id from mp_user where username like '大%'");

and  or 的使用
// WHERE (username LIKE ? AND ( (email IS NOT NULL OR age <= ?) ))
query.likeLeft("username", "翔").and(wp -> wp.isNotNull("email").or().le("age", 80));
// WHERE (username LIKE ? OR ( (email IS NOT NULL AND age >= ?) ))
query.like("username", "雨").or(wp -> wp.isNotNull("email").ge("age", 89));

   () 优先的设定 和 last取值
// WHERE (( (email IS NOT NULL OR age <= ?) ) AND username LIKE ?)  ORDER BY age ASC limit 2     
        query.nested(wp -> wp.isNotNull("email").or().le("age", 31)).like("username", "张")
        .orderByAsc("age").last("limit 2");

    // (age IN (?,?,?)) 
        query.in("age", Arrays.asList(25,28,32));

 // id, username  排除属性: 用!和&&进行修饰 
        query.select(User.class , wp -> wp.getColumn().equals("id")||wp.getColumn().equals("username")).le("age", 100);
// 当属性和列名不一致的时候不要使用下面的方式
//        query.select("id","username").le("age", 100);

//condition 判断条件是否执行
public Children like(boolean condition, R column, Object val) 
query.like(StringUtils.isNotEmpty(name), "username",name)

query.select("manager_id","avg(age) as avg", "min(age) as min", "max(age) as max")
        .groupBy("manager_id").having("sum(age) < {0}", 500);
List<Map<String, Object>> list = userMapper.selectMaps(query);
selectObject 返回一列
selectOne 返回一行,多了报错
selectCount int
selectMaps 适用于非全量数据的返回