Mybatis中@select註解聯合查詢
阿新 • • 發佈：2022-04-01
前言
在專案中經常會使用到一些簡單的聯合查詢獲取對應的資料資訊，我們常規都是會根據對應的mapper介面寫對應的mapper.xml的來通過對應的業務方法來呼叫獲取，針對這一點本人感覺有點繁瑣，就對@select註解聯合查詢進行探索和嘗試，並將自己總結的分享給大家，有不到之處，敬請大家批評指正！！！
一.pom.xml所用到依賴如下
<dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-web</artifactId> </dependency> <dependency> <groupId>org.projectlombok</groupId> <artifactId>lombok</artifactId> <optional>true</optional> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-test</artifactId> <scope>test</scope> </dependency> <dependency> <groupId>org.mybatis.spring.boot</groupId> <artifactId>mybatis-spring-boot-starter</artifactId> <version>2.2.0</version> </dependency> <dependency> <groupId>mysql</groupId> <artifactId>mysql-connector-java</artifactId> <version>5.1.38</version> </dependency>
二.application.yml的配置如下：
server: port: 8888 spring: datasource: driver-class-name: com.mysql.jdbc.Driver url: jdbc:mysql://localhost:3306/project?useUnicode=true&characterEncoding=UTF8&zeroDateTimeBehavior=convertToNull&useSSL=false username: root password: 123456 mybatis: type-aliases-package: com.songwp.snowflake.entity mapper-locations: classpath:mybatis/mapper/*.xml configuration: log-impl: org.apache.ibatis.logging.stdout.StdOutImpl
三.資料庫測試表
-- ---------------------------- -- Table structure for sys_dept -- 部門表 -- ---------------------------- DROP TABLE IF EXISTS `sys_dept`; CREATE TABLE `sys_dept` ( `id` varchar(50) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NOT NULL COMMENT '部門ID', `user_id` varchar(50) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci DEFAULT NULL COMMENT '使用者ID', `dept_name` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci DEFAULT NULL COMMENT '部門名稱', `parent_id` varchar(50) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci DEFAULT NULL COMMENT '父級部門ID', `parent_name` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci DEFAULT NULL COMMENT '父級部門名稱', `status` int(5) DEFAULT 0 COMMENT '部門狀態：0-正常 1-禁用', PRIMARY KEY (`id`) USING BTREE ) ENGINE = InnoDB CHARACTER SET = utf8mb4 COLLATE = utf8mb4_general_ci ROW_FORMAT = Compact; -- ---------------------------- -- Records of sys_dept -- ---------------------------- INSERT INTO `sys_dept` VALUES ('5a8f893eedef4eafbc66feded3541c0f', '4117460f-20f7-47e7-bf8a-507a32880c06', '集團本部', 'GS-001', '集團本部', 0); INSERT INTO `sys_dept` VALUES ('6271dd03e426400b9fd001bae9074efc', '4117460f-20f7-47e7-bf8a-507a32880c06', '財務部門', 'GS-003', '集團本部', 0); INSERT INTO `sys_dept` VALUES ('f33503159a084e73b4e1313932cc9629', '4117460f-20f7-47e7-bf8a-507a32880c06', '研發部門', 'GS-002', '集團本部', 0); -- ---------------------------- -- Table structure for sys_user -- 使用者表 -- ---------------------------- DROP TABLE IF EXISTS `sys_user`; CREATE TABLE `sys_user` ( `id` varchar(50) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NOT NULL COMMENT '主鍵ID', `username` varchar(50) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NOT NULL COMMENT '使用者名稱', `nickname` varchar(50) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NOT NULL COMMENT '真實姓名', `password` varchar(50) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NOT NULL COMMENT '密碼', `gender` int(5) DEFAULT 1 COMMENT '性別：0-女 1-男', `age` int(5) DEFAULT NULL COMMENT '年齡', `phone` varchar(20) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci DEFAULT NULL COMMENT '聯絡電話', `address` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci DEFAULT NULL COMMENT '住址', `status` int(5) DEFAULT 0 COMMENT '使用者狀態：0-正常 1-凍結 2- 已登出', `birthday` date DEFAULT NULL COMMENT '生日', `create_time` datetime DEFAULT NULL COMMENT '新增時間', `create_user` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci DEFAULT NULL COMMENT '建立人', `update_time` datetime DEFAULT NULL COMMENT '修改時間', `update_user` varchar(0) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci DEFAULT NULL COMMENT '修改人', `remark` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci DEFAULT NULL COMMENT '備註', PRIMARY KEY (`id`) USING BTREE ) ENGINE = InnoDB CHARACTER SET = utf8mb4 COLLATE = utf8mb4_general_ci ROW_FORMAT = Compact; -- ---------------------------- -- Records of sys_user -- ---------------------------- INSERT INTO `sys_user` VALUES ('4117460f-20f7-47e7-bf8a-507a32880c06', 'zs', '張三', '123456', 0, 25, '13888888888', '陝西西安', 0, '1996-05-07', '2022-03-28 10:17:54', '張三', NULL, NULL, NULL); INSERT INTO `sys_user` VALUES ('fb962a7f-3a61-4312-820c-9e67eefaa74a', 'zll', '趙老六', '123456', 1, 28, '13666666666', '陝西西安', 0, '1992-05-07', '2022-03-28 10:14:45', '趙老六', NULL, NULL, NULL);
四.@select註解中sql
假設我想使用者名稱(username)為“z's”和密碼(password)為“123456”的條件下使用者的資訊和對應部門的資訊為例：
SELECT u.username, u.PASSWORD, u.nickname, u.phone, u.gender, u.address, d.id AS dept_id, d.dept_name, d.STATUS AS dept_status FROM sys_user u INNER JOIN sys_dept d ON u.id = d.user_id WHERE u.username = 'zs' AND u.PASSWORD = '123456'
Navicat中結果執行如下：
五.mapper介面
@Select("<script> SELECT " +
"u.username," +
"u.password," +
"u.nickname," +
"u.phone," +
"u.gender," +
"u.address," +
"d.id as dept_id," +
"d.dept_name," +
"d.status as dept_status " +
"from" +
" sys_user u" +
" inner join sys_dept d on u.id = d.user_id " +
" where u.username = #{username} <when test='password !=null'> " +
" and u.password = #{password} </when> </script>")
List<Map> getByParmsMap(String username, String password);
1、@Select註解基本用法
@Select註解的目的是為了取代xml中的select標籤，只作用於方法上面。下面看一下@Select註解的原始碼介紹：
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
public @interface Select
{
String[] value();
}
從上述可以看到兩點資訊：
（1）@Select註解只能修飾方法
（2）@Select註解的值是字元陣列。
所以，@Select註解的用法是這樣的：
@Select({ "select * from xxx", "select * from yyy" })
Person selectPersonById(Integer id);
雖然@Select註解的值是字元陣列，但是真正生效的應該是最後那條SQL語句。這一點請大家要留意一下。
2、@Select註解動態SQL拼寫
普通的字串值，只能實現變數的替換功能，如下所示，
@Select("select * from t_person where id = #{id}")
Person selectPersonById(Integer id);
如果要想實現複雜的邏輯判斷，則需要使用標籤，如下所示：
@Select("<script> select * from t_person where id = #{id}
<when test='address !=null'> and address = #{address}
</when> </script>")
Person selectPersonById(Integer id);
其實，標籤並非是@Select註解專用的，其他的註解，例如@Insert，@Update等等，都可以使用的。
六.業務層service介面
List<Map> getByParmsMap(String username, String password);
七.業務實現類的方法
public List<Map> getByParmsMap(String username, String password) { return userMapper.getByParmsMap(username,password); }
八.控制器controller方法
@RequestMapping(value = {"/getByParmsMap"}, method = RequestMethod.GET)
@ResponseBody
public List<Map> getByParmsMap(@RequestParam("username")String username,@RequestParam("password")String password){
return userService.getByParmsMap(username,password);
}
九.Postman介面呼叫如下
[ { "password": "123456", "address": "陝西西安", "gender": 0, "phone": "13888888888", "nickname": "張三", "dept_name": "集團本部", "dept_status": 0, "dept_id": "5a8f893eedef4eafbc66feded3541c0f", "username": "zs" }, { "password": "123456", "address": "陝西西安", "gender": 0, "phone": "13888888888", "nickname": "張三", "dept_name": "財務部門", "dept_status": 0, "dept_id": "6271dd03e426400b9fd001bae9074efc", "username": "zs" }, { "password": "123456", "address": "陝西西安", "gender": 0, "phone": "13888888888", "nickname": "張三", "dept_name": "研發部門", "dept_status": 0, "dept_id": "f33503159a084e73b4e1313932cc9629", "username": "zs" } ]
如下圖所示：