MyBatis图文并茂讲解注解开发一对一查询

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

一对一查询

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

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};

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);
}

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();
}

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：

一对一配置总结

来源：https://yangyongli.blog.csdn.net/article/details/125590508