MyBatis注解开发之一对一查询

Posted 2022-07-05 流楚丶格念

文章目录

• 0. MyBatis的注解实现复杂映射开发
• 1. 一对一查询
• • 1.1 一对一查询的模型
  • 1.2 一对一查询的语句
  • 1.3 创建PersonMapper接口
  • 1.4 使用注解配置Mapper
  • 1.5 测试类
  • 1.6 一对一配置总结

0. MyBatis的注解实现复杂映射开发

实现复杂关系映射之前我们可以在映射文件中通过配置来实现，使用注解开发后，我们可以使用@Results注解，@Result注解，@One注解，@Many注解组合完成复杂关系的配置

1. 一对一查询

1.1 一对一查询的模型

一对一查询的需求：查询一个用户信息，与此同时查询出该用户对应的身份证信息

1.2 一对一查询的语句

创建数据库：

-- ----------------------------
-- Table structure for card
-- ----------------------------
DROP TABLE IF EXISTS `card`;
CREATE TABLE `card`  (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `number` varchar(30) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci NULL DEFAULT NULL,
  `pid` int(11) NULL DEFAULT NULL,
  PRIMARY KEY (`id`) USING BTREE,
  INDEX `cp_fk`(`pid`) USING BTREE
) ENGINE = MyISAM AUTO_INCREMENT = 4 CHARACTER SET = utf8mb4 COLLATE = utf8mb4_unicode_ci ROW_FORMAT = Dynamic;

-- ----------------------------
-- Records of card
-- ----------------------------
INSERT INTO `card` VALUES (1, '12345', 1);
INSERT INTO `card` VALUES (2, '23456', 2);
INSERT INTO `card` VALUES (3, '34567', 3);

-- ----------------------------
-- Table structure for classes
-- ----------------------------
DROP TABLE IF EXISTS `classes`;
CREATE TABLE `classes`  (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `NAME` varchar(20) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci NULL DEFAULT NULL,
  PRIMARY KEY (`id`) USING BTREE
) ENGINE = MyISAM AUTO_INCREMENT = 3 CHARACTER SET = utf8mb4 COLLATE = utf8mb4_unicode_ci ROW_FORMAT = Dynamic;

-- ----------------------------
-- Records of classes
-- ----------------------------
INSERT INTO `classes` VALUES (1, '极地一班');
INSERT INTO `classes` VALUES (2, '极地二班');

-- ----------------------------
-- Table structure for course
-- ----------------------------
DROP TABLE IF EXISTS `course`;
CREATE TABLE `course`  (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `NAME` varchar(20) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci NULL DEFAULT NULL,
  PRIMARY KEY (`id`) USING BTREE
) ENGINE = MyISAM AUTO_INCREMENT = 3 CHARACTER SET = utf8mb4 COLLATE = utf8mb4_unicode_ci ROW_FORMAT = Dynamic;

-- ----------------------------
-- Records of course
-- ----------------------------
INSERT INTO `course` VALUES (1, '语文');
INSERT INTO `course` VALUES (2, '数学');

-- ----------------------------
-- Table structure for person
-- ----------------------------
DROP TABLE IF EXISTS `person`;
CREATE TABLE `person`  (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `NAME` varchar(20) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci NULL DEFAULT NULL,
  `age` int(11) NULL DEFAULT NULL,
  PRIMARY KEY (`id`) USING BTREE
) ENGINE = MyISAM AUTO_INCREMENT = 4 CHARACTER SET = utf8mb4 COLLATE = utf8mb4_unicode_ci ROW_FORMAT = Dynamic;

-- ----------------------------
-- Records of person
-- ----------------------------
INSERT INTO `person` VALUES (1, '张三', 23);
INSERT INTO `person` VALUES (2, '李四', 24);
INSERT INTO `person` VALUES (3, '王五', 25);

-- ----------------------------
-- Table structure for stu_cr
-- ----------------------------
DROP TABLE IF EXISTS `stu_cr`;
CREATE TABLE `stu_cr`  (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `sid` int(11) NULL DEFAULT NULL,
  `cid` int(11) NULL DEFAULT NULL,
  PRIMARY KEY (`id`) USING BTREE,
  INDEX `sc_fk1`(`sid`) USING BTREE,
  INDEX `sc_fk2`(`cid`) USING BTREE
) ENGINE = MyISAM AUTO_INCREMENT = 5 CHARACTER SET = utf8mb4 COLLATE = utf8mb4_unicode_ci ROW_FORMAT = Fixed;

-- ----------------------------
-- Records of stu_cr
-- ----------------------------
INSERT INTO `stu_cr` VALUES (1, 1, 1);
INSERT INTO `stu_cr` VALUES (2, 1, 2);
INSERT INTO `stu_cr` VALUES (3, 2, 1);
INSERT INTO `stu_cr` VALUES (4, 2, 2);

-- ----------------------------
-- Table structure for student
-- ----------------------------
DROP TABLE IF EXISTS `student`;
CREATE TABLE `student`  (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `NAME` varchar(30) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci NULL DEFAULT NULL,
  `age` int(11) NULL DEFAULT NULL,
  `cid` int(11) NULL DEFAULT NULL,
  PRIMARY KEY (`id`) USING BTREE,
  INDEX `cs_fk`(`cid`) USING BTREE
) ENGINE = MyISAM AUTO_INCREMENT = 5 CHARACTER SET = utf8mb4 COLLATE = utf8mb4_unicode_ci ROW_FORMAT = Dynamic;

-- ----------------------------
-- Records of student
-- ----------------------------
INSERT INTO `student` VALUES (1, '张三', 23, 1);
INSERT INTO `student` VALUES (2, '李四', 24, 1);
INSERT INTO `student` VALUES (3, '王五', 25, 2);
INSERT INTO `student` VALUES (4, '赵六', 26, 2);

SET FOREIGN_KEY_CHECKS = 1;

对应的sql语句：

SELECT * FROM card；

SELECT * FROM person WHERE id=#id;

1.3 创建PersonMapper接口

public interface PersonMapper 
    //根据id查询
    @Select("SELECT * FROM person WHERE id=#id")
    public abstract Person selectById(Integer id);

1.4 使用注解配置Mapper

public interface CardMapper 
    //查询全部
    @Select("SELECT * FROM card")
    @Results(
            @Result(column = "id",property = "id"),
            @Result(column = "number",property = "number"),
            @Result(
                    property = "p",             // 被包含对象的变量名
                    javaType = Person.class,    // 被包含对象的实际数据类型
                    column = "pid",             // 根据查询出的card表中的pid字段来查询person表
                    /*
                        one、@One 一对一固定写法
                        select属性：指定调用哪个接口中的哪个方法
                     */
                    one = @One(select = "com.yyl.one_to_one.PersonMapper.selectById")
            )
    )
    public abstract List<Card> selectAll();

1.5 测试类

public class Test01 
    @Test
    public void selectAll() throws Exception
        //1.加载核心配置文件
        InputStream is = Resources.getResourceAsStream("MyBatisConfig.xml");

        //2.获取SqlSession工厂对象
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(is);

        //3.通过工厂对象获取SqlSession对象
        SqlSession sqlSession = sqlSessionFactory.openSession(true);

        //4.获取CardMapper接口的实现类对象
        CardMapper mapper = sqlSession.getMapper(CardMapper.class);

        //5.调用实现类对象中的方法，接收结果
        List<Card> list = mapper.selectAll();

        //6.处理结果
        for (Card card : list) 
            System.out.println(card);
        

        //7.释放资源
        sqlSession.close();
        is.close();
    

运行结果如下：

1.6 一对一配置总结

注解	说明
@Results	封装映射关系的父注解。 Result[] value()：定义了 Result 数组
@Result	封装映射关系的子注解。 column 属性：查询出的表中字段名称 property 属性：实体对象中的属性名称 javaType 属性：被包含对象的数据类型 one 属性：一对一查询固定属性
@One	一对一查询的注解。 select 属性：指定调用某个接口中的方法