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解决mybatis一对多查询问题时的只显示一条数据的问题（查询部门的同时把所属部门的员工信息查出来）关联查询

程序员文章站 2024-03-20 11:25:16
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博客里的一些文章过于杂乱萌生了自己写一篇的想法

出现该错误的原因是两张表的主键名称一致导致的比如下面
解决mybatis一对多查询问题时的只显示一条数据的问题（查询部门的同时把所属部门的员工信息查出来）关联查询
两张表的主键名称都是id,解决方法就是写查询语句的的时候给主键id取别名就行了（我用的查询方式是关联查询，先查询在集中映射）
下面是我的项目框架：
解决mybatis一对多查询问题时的只显示一条数据的问题（查询部门的同时把所属部门的员工信息查出来）关联查询
我的maven依赖：

<dependencies>
		<!-- mybatis -->
		<dependency>
			<groupId>org.mybatis</groupId>
			<artifactId>mybatis</artifactId>
			<version>3.4.0</version>
		</dependency>
		<!-- mysql数据库驱动 -->
		<dependency>
			<groupId>mysql</groupId>
			<artifactId>mysql-connector-java</artifactId>
			<version>5.1.39</version>
		</dependency>
		<!-- juint测试框架 -->
		<dependency>
			<groupId>junit</groupId>
			<artifactId>junit</artifactId>
			<version>4.12</version>
		</dependency>
		<!-- lombok依赖 -->
		<dependency>
			<groupId>org.projectlombok</groupId>
			<artifactId>lombok</artifactId>
			<version>1.18.12</version>
		</dependency>
		<!--log4j依赖 -->
		<dependency>
			<groupId>log4j</groupId>
			<artifactId>log4j</artifactId>
			<version>1.2.17</version>
		</dependency>
		<!--slf4j依赖 -->
		<dependency>
			<groupId>org.slf4j</groupId>
			<artifactId>slf4j-api</artifactId>
			<version>1.7.25</version>
		</dependency>
		<dependency>
			<groupId>org.slf4j</groupId>
			<artifactId>slf4j-log4j12</artifactId>
			<version>1.7.28</version>
		</dependency>
	</dependencies>

我的配置文件：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN" 
"http://mybatis.org/dtd/mybatis-3-config.dtd" >
<configuration>

<settings>
<setting name="mapUnderscoreToCamelCase" value="true"/>
</settings>
	<environments default="development">
		<environment id="development">
			<transactionManager type="MANAGED" />
			<dataSource type="POOLED">
				<property name="driver" value="com.mysql.jdbc.Driver" />
				<property name="url" value="jdbc:mysql://localhost:3306/jtsys?useSSL=true" />
				<property name="username" value="root" />
				<property name="password" value="root" />
			</dataSource>
		</environment>
	</environments>
	<!-- <mappers> <mapper resource="mappers/UserMapper.xml" /> </mappers> -->
	<mappers>
	<mapper resource="mappers/UserMapper.xml"/>
    <mapper resource="mappers/DeptMapper.xml"/>
	</mappers>
</configuration>

User实体：

@Data //这个注解相当于setter/getter/toString
public class User {
	
	 private Integer id;
	 private String username;
	 private String password;
	 private String salt;
	 private Integer deptId;
	 private String email;
	 private String mobile;
	 private Integer valid=1;
	 private Date createdTime;
	 private Date modifiedTime;
	 private String modifiedUser;
	 private String createdUser;
	 // 查询用户的时候，将部门的查询结果映射到部门对象
	 private Dept dept;
}

Dept实体：

@Data
public class Dept {

	private Integer id;
	private String name;
	private Integer parentId;
	private Integer  sort;
	private String note;
	private Date createdTime;
	private Date modifiedTime;
	private String createdUSer;
	private String modifiedUser;
	//查询部门的时候将用户的结果映射到User对象
	private List<User> users;
}

DeptDao接口：

public interface DeptDao {
	List<Dept> selectDeptUsers();
}

DeptMapper.xml文件：

<mapper namespace="com.cn.dao.DeptDao">
	<select id="selectDeptUsers" resultMap="selectdepts">
		SELECT d.*,
		u.id as uid,**//这里是用户表主键给起了别名uid**
		u.username,
		u.password,
		u.salt,
		u.deptId,
		u.email,
		u.mobile,
		u.valid,
		u.createdTime,
		u.modifiedTime,
		u.modifiedUser,
		u.createdUser
		FROM sys_depts d 
		RIGHT JOIN
		sys_users u ON d.id=u.deptId
	</select>

	<resultMap type="com.cn.entity.Dept" id="selectdepts">
		<id property="id" column="id" />
		//你如果想要部门表里的所有的数据，就要全部映射
		<result property="name" column="name"/>
        <result property="parentId" column="parentId"/>
        <result property="sort" column="sort"/>
        <result property="note" column="note"/>
        <result property="createdTime" column="createdTime"/>
        <result property="modifiedTime" column="modifiedTime"/>
        <result property="createdUSer" column="createdUSer"/>
        <result property="modifiedUser" column="modifiedUser"/>
		<collection property="users" ofType="com.cn.entity.User">
		    // id这里用的起的别名uid
			<id property="id" column="uid" />
			//用户表只要id和用户名和邮箱和手机号
			<result property="username" column="username" />
			<result property="email" column="email" />
			<result property="mobile" column="mobile" />	
		</collection>
	</resultMap>
</mapper>

测试：

public class DeptTests {
	
	 public static SqlSessionFactory sqlSessionFactory;
     public SqlSession sqlSession;
     //添加UserMapper接口
     public DeptMapper dp;
     //通过SqlSessionFactoryBuilder构造SqlSessionFactory实例
     @BeforeClass
     public static void testBefore() throws IOException {
     InputStream in = Resources.getResourceAsStream("mybatis-config.xml");
       sqlSessionFactory = new SqlSessionFactoryBuilder().build(in);
     }
     // 每个单元测试方法(添加@Test注解的方法)在执行前，创建一个新的SqlSession实例，并获得UserMapper接口的动态代理对象
     @Before
     public void before() {
           sqlSession = sqlSessionFactory.openSession();
           dp = sqlSession.getMapper(DeptMapper.class);
     }		
	 @After
     public void after() {
           sqlSession.close();
     }
	 
	 @Test
	 public void selectUsersDept() {
		     List<Dept> deptsusers = dp.selectDeptUsers();
		     deptsusers.forEach(System.out::println);
	 }

}

控值台结果：

Dept(id=2, name=设计部, parentId=2, sort=1, note=设计, createdTime=Thu Apr 19 18:59:09 CST 2018, modifiedTime=Thu Apr 19 18:59:09 CST 2018, createdUSer=admin, modifiedUser=admin, users=[User(id=4, username=王五, password=null, salt=null, deptId=null, email=aaa@qq.com, mobile=null, valid=1, createdTime=null, modifiedTime=null, modifiedUser=null, createdUser=null, dept=null), User(id=6, username=王花, password=null, salt=null, deptId=null, email=aaa@qq.com, mobile=null, valid=1, createdTime=null, modifiedTime=null, modifiedUser=null, createdUser=null, dept=null), User(id=16, username=李华, password=null, salt=null, deptId=null, email=aaa@qq.com, mobile=null, valid=1, createdTime=null, modifiedTime=null, modifiedUser=null, createdUser=null, dept=null)])
Dept(id=3, name=营销部, parentId=1, sort=2, note=营销, createdTime=Thu Apr 19 19:15:05 CST 2018, modifiedTime=Thu Apr 19 19:15:05 CST 2018, createdUSer=null, modifiedUser=null, users=[User(id=1, username=admin, password=null, salt=null, deptId=null, email=aaa@qq.com, mobile=null, valid=1, createdTime=null, modifiedTime=null, modifiedUser=null, createdUser=null, dept=null), User(id=3, username=李四, password=null, salt=null, deptId=null, email=aaa@qq.com, mobile=null, valid=1, createdTime=null, modifiedTime=null, modifiedUser=null, createdUser=null, dept=null), User(id=12, username=user-001, password=null, salt=null, deptId=null, email=aaa@qq.com, mobile=null, valid=1, createdTime=null, modifiedTime=null, modifiedUser=null, createdUser=null, dept=null), User(id=13, username=user-c, password=null, salt=null, deptId=null, email=aaa@qq.com, mobile=null, valid=1, createdTime=null, modifiedTime=null, modifiedUser=null, createdUser=null, dept=null), User(id=15, username=user-b, password=null, salt=null, deptId=null, email=aaa@qq.com, mobile=null, valid=1, createdTime=null, modifiedTime=null, modifiedUser=null, createdUser=null, dept=null)])
Dept(id=4, name=人事部, parentId=2, sort=1, note=管理, createdTime=Sun Apr 22 18:10:58 CST 2018, modifiedTime=Sun Apr 22 22:11:47 CST 2018, createdUSer=null, modifiedUser=null, users=[User(id=2, username=张三, password=null, salt=null, deptId=null, email=aaa@qq.com, mobile=null, valid=1, createdTime=null, modifiedTime=null, modifiedUser=null, createdUser=null, dept=null)])

打完收工！！！
还有一种分段查询的方式，其他不变只是代码不同，同样也能查出来在我下一篇博客

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