mybatis-plus-Chain

官方文档

本文与官网大多数一致，只是在示例中加入了一些实际验证的代码，日志可能和与官网略有出入（预估是因为版本原因）

本文测试代码中mybatis-plus依赖:

    <dependency>
        <groupId>com.baomidou</groupId>
        <artifactId>mybatis-plus-spring-boot3-starter</artifactId>
        <version>3.5.7</version>
    </dependency>

Chain 是 Mybatis-Plus 提供的一种链式编程风格，它允许开发者以更加简洁和直观的方式编写数据库操作代码。Chain 分为 query 和 update 两大类，分别用于查询和更新操作。每类又分为普通链式和 lambda 链式两种风格，其中 lambda 链式提供了类型安全的查询条件构造，但不支持 Kotlin。

下面分别对Service，Mapper，entity这三个不同层操作链式操作数据库做演示：

    @Data
    @TableName("user")
    public class UserPO implements Serializable {

        private static final long serialVersionUID = 1L;
        @TableId(value = "id", type = IdType.AUTO)
        private Integer id;
        @TableField(updateStrategy = FieldStrategy.NOT_NULL)
        private String username;
        private Integer age;
        private Integer gender;
        @TableField(fill = FieldFill.UPDATE)
        private String email;
        private String phoneNumber;

    //    @TableLogic(value="1",delval = "0")
        private String state;


    }

    @Resource
    private IUserService userService;//IUserService实现类继承了Iservice


    @Resource
    private UserMapper userMapper;//UserMapper实现类继承了BaseMapper

    /*************************************************************************/
   @Test
    public void testQuery() {
        userService.query().eq("username", "张三").list();
    }
    // ==>  Preparing: SELECT id,username,age,gender,email,phone_number,state FROM user WHERE (username = ?)
    // ==> Parameters: 张三(String)
    // <==    Columns: id, username, age, gender, email, phone_number, state
    // <==        Row: 1, 张三, 22, 1, zhangsan@email.com, 1890000001, null
    // <==      Total: 1

    /*************************************************************************/
    @Test
    public void testUpdate() {
        UserPO userPO = new UserPO();
        userPO.setUsername("张三");
        userPO.setAge(44);
        userService.lambdaUpdate().set(true, UserPO::getAge, userPO.getAge()).eq(UserPO::getUsername, userPO.getUsername()).update();
        
    }
    // ==>  Preparing: UPDATE user SET age=? WHERE (username = ?)
    // ==> Parameters: 44(Integer), 张三(String)
    // <==    Updates: 1

    /*************************************************************************/
    @Test
    public void testQuery2() {
        queryChain(userMapper).eq("username","张三").list();
    }
    // ==>  Preparing: SELECT id,username,age,gender,email,phone_number,state FROM user WHERE (username = ?)
    // ==> Parameters: 张三(String)
    // <==    Columns: id, username, age, gender, email, phone_number, state
    // <==        Row: 1, 张三, 44, 1, zhangsan@email.com, 1890000001, null
    // <==      Total: 1


    /*************************************************************************/
    @Test
    public void testUpdate2() {
        updateChain(userMapper).eq("username","张三").set("age",44).update();
    }
    // ==>  Preparing: UPDATE user SET age=? WHERE (username = ?)
    // ==> Parameters: 44(Integer), 张三(String)
    // <==    Updates: 1

    /*************************************************************************/
    @Test
    public void testQuery33() {
        queryChain(UserPO.class).eq("username","张三").list();
    }
    //==>  Preparing: SELECT id,username,age,gender,email,phone_number,state FROM user WHERE (username = ?)
    // ==> Parameters: 张三(String)
    // <==    Columns: id, username, age, gender, email, phone_number, state
    // <==        Row: 1, 张三, 44, 1, zhangsan@email.com, 1890000001, null
    // <==      Total: 1

    /*************************************************************************/
    @Test
    public void testUpdate3() {
        updateChain(UserPO.class).eq("username","张三").set("age",55).update();
    }
    // ==>  Preparing: UPDATE user SET age=? WHERE (username = ?)
    // ==> Parameters: 55(Integer), 张三(String)
    // <==    Updates: 1

关于操作符说明后期单独说明。