The main content is the
collection tag: used to deal with one-to-many relationship tags
property: package relationship property name
javaType: relationship property type
ofType: used to write the generic type of the relationship property type
创建员工表 部门表
#部门表
create table t_dept(
id int(6) PRIMARY key auto_increment,
name VARCHAR(40)
);
#员工表
CREATE TABLE t_emp(
id int(6) primary key auto_increment,
ame VARCHAR(40),
age int(3),
bir TIMESTAMP,
deptid int(6) REFERENCES t_dept(id)
);
员工和部门对应实体类
public class Emp {
private Integer id;
private String name;
private Integer age;
private Date bir;
private Integer deptid;
private Dept dept;
//set() get() toString()
}
public class Dept {
private Integer id;
private String name;
private List<Emp> emps;
//set() get() toString()
}
1. Query all departments and query the employee information of each department
public interface DeptDAO {
//查询所有部门并查询出每个部门的员工信息
List<Dept> queryAll();
}
DeptDAO.xml
<mapper namespace="com.xxx.dao.DeptDAO">
<resultMap id="deptMap" type="com.xxx.entity.Dept">
<id column="id" property="id"/>
<result column="name" property="name"/>
<!--封装员工信息
collection:用来处理一对多关联关系标签
property：封装关系属性名
javaType：关系属性类型
ofType：用来书写关系属性类型中泛型的类型
-->
<collection property="emps" javaType="java.util.List" ofType="com.xxx.entity.Emp">
<id column="eid" property="id"/>
<result column="ename" property="name"/>
<result column="age" property="age"/>
<result column="bir" property="bir"/>
<result column="deptid" property="deptid"/>
</collection>
</resultMap>
<!--查詢所有-->
<select id="queryAll" resultMap="deptMap">
SELECT
t.id,
t.name,
e.id eid,
e.name ename,
e.age,
e.bir,
e.deptid
FROM
t_dept t
LEFT JOIN t_emp e ON t.id = e.deptid
</select>
</mapper>
测试
public class TestDept {
private InputStream in;
private SqlSession session;
private DeptDAO deptDAO;
@Before
public void init() throws IOException {
//1.读取配置文件
in = Resources.getResourceAsStream("SqlMapConfig.xml");
//2创建工厂
SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();
SqlSessionFactory factory = builder.build(in);
session = factory.openSession();
deptDAO = session.getMapper(DeptDAO.class);
}
@After
public void destory() throws IOException {
//提交事務
session.commit();
session.close();
in.close();
}
@Test
public void TestQueryAll(){
deptDAO.queryAll().forEach(dept -> {
System.out.println("部门信息"+dept);
dept.getEmps().forEach(emp->{
System.out.println("员工信息"+emp);
});
System.out.println("-----------------");
});
}
}
The output is:
部门信息Dept{id=1, name='研发部'}
员工信息Emp{id=1, name='小张1', age=34, bir=Thu Aug 22 18:33:14 CST 2019, deptid=1}
员工信息Emp{id=3, name='小丽1', age=45, bir=Fri Feb 01 18:34:09 CST 2019, deptid=1}
-----------------
部门信息Dept{id=2, name='教学部'}
员工信息Emp{id=2, name='小王2', age=23, bir=Tue Feb 28 18:33:40 CST 2017, deptid=2}
员工信息Emp{id=4, name='小李2', age=32, bir=Thu Jan 06 18:34:55 CST 2000, deptid=2}
-----------------
2. Query employee information and display the information of the employee's department
EmpDAO.java
public interface EmpDAO {
//查询员工信息并显示员工所在部门的信息
List<Emp> queryAll();
}
EmpDAO.xml
<mapper namespace="com.xx.dao.EmpDAO">
<resultMap id="empMap" type="com.xx.entity.Emp">
<id column="id" property="id"/>
<result column="name" property="name"/>
<result column="age" property="age"/>
<result column="bir" property="bir"/>
<result column="deptid" property="deptid"/>
<association property="dept" javaType="com.xx.entity.Dept">
<id column="tid" property="id"/>
<result column="tname" property="name"/>
</association>
</resultMap>
<!--查詢所有-->
<select id="queryAll" resultMap="empMap">
SELECT
e.id,
e.NAME,
age,
bir,
deptid,
t.NAME tname,
t.id tid
FROM
t_emp e
LEFT JOIN t_dept t ON e.deptid = t.id
</select>
</mapper>
测试
public class TestEmp {
private InputStream in;
private SqlSession session;
private EmpDAO empDAO;
@Before
public void init() throws IOException {
//1.读取配置文件
in = Resources.getResourceAsStream("SqlMapConfig.xml");
//2创建工厂
SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();
SqlSessionFactory factory = builder.build(in);
session = factory.openSession();
empDAO = session.getMapper(EmpDAO.class);
}
@After
public void destory() throws IOException {
//提交事務
session.commit();
session.close();
in.close();
}
@Test
public void TestQueryAll(){
empDAO.queryAll().forEach(emp -> {
System.out.println("员工信息"+emp+emp.getDept().getName()); });
}
}
Register mapper in the main configuration file
<mappers>
<mapper resource="com/xx/dao/DeptDAO.xml"></mapper>
<mapper resource="com/xx/dao/EmpDAO.xml"></mapper>
</mappers>
Output:
员工信息Emp{id=1, name='小张1', age=34, bir=Thu Aug 22 18:33:14 CST 2019, deptid=1}研发部
员工信息Emp{id=2, name='小王2', age=23, bir=Tue Feb 28 18:33:40 CST 2017, deptid=2}教学部
员工信息Emp{id=3, name='小丽1', age=45, bir=Fri Feb 01 18:34:09 CST 2019, deptid=1}研发部
员工信息Emp{id=4, name='小李2', age=32, bir=Thu Jan 06 18:34:55 CST 2000, deptid=2}教学部