为什么要引入 Mybatis 增强插件

从一个业务开发者的角度来看，这种类似的增强框架使用起来很爽。

单表情况下不必再把思路从 Service 切换到 Mapper，从业务思维（业务流程）切换到数据库思维（数据库字段，编写），一定程度上减少了代码的开发量。
易于维护数据库增改删字段不必再去 xml 里改，一处Refactor，多处修改，也可以避免一些cv 过程中的低级错误

Mybatis-Flex 与 Mybatis-Plus 的区别

基础查询:

Mybatis-Flex:
查询:

QueryWrapper query = QueryWrapper.create()
        .where(EMPLOYEE.LAST_NAME.like(searchWord)) //条件为null时自动忽略
        .and(EMPLOYEE.GENDER.eq(1))
        .and(EMPLOYEE.AGE.gt(24));
List<Employee> employees = employeeMapper.selectListByQuery(query);

Mybatis-Plus：

LambdaQueryWrapper<Employee> queryWrapper = Wrappers.<Employee>lambdaQuery()
        .like(StringUtils.isNotEmpty(searchWord), Employee::getUserName,"B")
        .eq(Employee::getGender, 1)
        .gt(Employee::getAge, 24);
List<Employee> employees = employeeMapper.selectList(queryWrapper);

更新:
Mybatis-Flex:

Account account = UpdateEntity.of(Account.class);
account.setId(100); //设置主键
account.setUserName("michael");
account.setAge(18);
account.setBirthday(null);

accountMapper.update(account);

Mybatis-Plus：

UpdateWrapper<Account> updateWrapper = new UpdateWrapper<>();
updateWrapper.eq("id", 100);
updateWrapper.set("user_name", "michael");
updateWrapper.set("age", 18);
updateWrapper.set("birthday", null);

accountMapper.update(null, updateWrapper);

查询集合函数：

Mybatis-Flex:

QueryWrapper query = QueryWrapper.create()
    .select(
        ACCOUNT.ID,
        ACCOUNT.USER_NAME,
        max(ACCOUNT.BIRTHDAY),
        avg(ACCOUNT.SEX).as("sex_avg")
    );
List<Employee> employees = employeeMapper.selectListByQuery(query);

Mybatis-Plus：

QueryWrapper<Employee> queryWrapper = Wrappers.query()
    .select(
        "id",
        "user_name",
        "max(birthday)",
        "avg(birthday) as sex_avg"
    );
List<Employee> employees = employeeMapper.selectList(queryWrapper);

联表查询 flex 是支持的 mp 不支持,虽然支持但是复杂联表可读性不高,个人觉得关于联表的 sql 还是自行维护在 xml 里面
附示例:

QueryWrapper query = QueryWrapper.create()
    .select().from(ACCOUNT)
    .leftJoin(ARTICLE).on(ACCOUNT.ID.eq(ARTICLE.ACCOUNT_ID))
    .where(ACCOUNT.AGE.ge(10));

List<Account> accounts = mapper.selectListByQuery(query);

QueryWrapper query = new QueryWrapper()
.select(
      ACCOUNT.ID
    , ACCOUNT.USER_NAME
    , ARTICLE.ID.as("articleId")
    , ARTICLE.TITLE)
.from(ACCOUNT.as("a"), ARTICLE.as("b"))
.where(ACCOUNT.ID.eq(ARTICLE.ACCOUNT_ID));