Springboot+mybatis+MySQL实现简单的多表查询
直接进入正题
1.首先我们新建一个数据库，再建两个表
tbl_employee表建表SQL语句
CREATE TABLE `tbl_employee` (
`id` int(200) NOT NULL AUTO_INCREMENT,
`last_name` varchar(255) DEFAULT NULL,
`email` varchar(255) DEFAULT NULL,
`gender` varchar(255) DEFAULT NULL,
`d_id` int(11) DEFAULT NULL,
PRIMARY KEY (`id`),
KEY `fk_emp_dept` (`d_id`),
CONSTRAINT `fk_emp_dept` FOREIGN KEY (`d_id`) REFERENCES `tbl_dept` (`id`) ON DELETE NO ACTION ON UPDATE CASCADE
) ENGINE=InnoDB AUTO_INCREMENT=8 DEFAULT CHARSET=utf8
tbl_dept表建表SQL语句
CREATE TABLE `tbl_dept` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`dept_name` varchar(255) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8
表建好之后，我们填入一些数据。如下：
图中画红圈的为关联部分，将两个表进行关联。
2.在平时我们需要分别查询每一个表的信息。
这里我们的需求是，我要查询这个人的名字顺便查到这个人属于哪个部门，这就需要多表联查了。
3.我们还用SpringBoot+mybatis创建一个项目。
4.代码如下：
Controller层
@RestController
public class EmployeeController {
@Autowired
private EmployeeService employeeService;
@RequestMapping(value = "/selectEmployee",method = RequestMethod.POST,headers = "Accept=application/json")
public HttpResponseEntity selectEmployee(@RequestBody Employee employee){
HttpResponseEntity httpResponseEntity = new HttpResponseEntity();
try {
Employee selectEmployee = employeeService.selectEmployee(employee);
httpResponseEntity.setCode(Constans.SUCCESS_CODE);
httpResponseEntity.setMessage(Constans.SELECT_EXIST_SUCCESS);
httpResponseEntity.setData(selectEmployee);
}catch (Exception e){
httpResponseEntity.setCode(Constans.ADD_EXIST_CODE);
httpResponseEntity.setMessage(Constans.SELECT_EXIST_MESSAGE);
}
return httpResponseEntity;
}
Service层
@Service
public class EmployeeService {
@Autowired
private EmployeeMapper employeeMapper;
@Transactional
public Employee selectEmployee(Employee employee) {
Employee selectEmployee = employeeMapper.selectEmployee(employee.getId());
return selectEmployee;
}
Mapper
Employee selectEmployee(Integer id);
5.创建两个实体类，代码如下：
Department
package com.springboot.dao.entity;
public class Department {
private Integer id;
private String departmentName;
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getDepartmentName() {
return departmentName;
}
public void setDepartmentName(String departmentName) {
this.departmentName = departmentName;
}
@Override
public String toString() {
return "Department{" +
"id=" + id +
", departmentName='" + departmentName + '\'' +
'}';
}
}
Employee
package com.springboot.dao.entity;
public class Employee {
/**
*
* This field was generated by MyBatis Generator.
* This field corresponds to the database column tbl_employee.id
*
* @mbg.generated
*/
private Integer id;
/**
*
* This field was generated by MyBatis Generator.
* This field corresponds to the database column tbl_employee.last_name
*
* @mbg.generated
*/
private String lastName;
/**
*
* This field was generated by MyBatis Generator.
* This field corresponds to the database column tbl_employee.email
*
* @mbg.generated
*/
private String email;
/**
*
* This field was generated by MyBatis Generator.
* This field corresponds to the database column tbl_employee.gender
*
* @mbg.generated
*/
private String gender;
/**
*
* This field was generated by MyBatis Generator.
* This field corresponds to the database column tbl_employee.d_id
*
* @mbg.generated
*/
private Integer dId;
/**
* This method was generated by MyBatis Generator.
* This method returns the value of the database column tbl_employee.id
*
* @return the value of tbl_employee.id
*
* @mbg.generated
*/
private Department dept;
public Department getDept() {
return dept;
}
public void setDept(Department dept) {
this.dept = dept;
}
public Integer getId() {
return id;
}
/**
* This method was generated by MyBatis Generator.
* This method sets the value of the database column tbl_employee.id
*
* @param id the value for tbl_employee.id
*
* @mbg.generated
*/
public void setId(Integer id) {
this.id = id;
}
/**
* This method was generated by MyBatis Generator.
* This method returns the value of the database column tbl_employee.last_name
*
* @return the value of tbl_employee.last_name
*
* @mbg.generated
*/
public String getLastName() {
return lastName;
}
/**
* This method was generated by MyBatis Generator.
* This method sets the value of the database column tbl_employee.last_name
*
* @param lastName the value for tbl_employee.last_name
*
* @mbg.generated
*/
public void setLastName(String lastName) {
this.lastName = lastName == null ? null : lastName.trim();
}
/**
* This method was generated by MyBatis Generator.
* This method returns the value of the database column tbl_employee.email
*
* @return the value of tbl_employee.email
*
* @mbg.generated
*/
public String getEmail() {
return email;
}
/**
* This method was generated by MyBatis Generator.
* This method sets the value of the database column tbl_employee.email
*
* @param email the value for tbl_employee.email
*
* @mbg.generated
*/
public void setEmail(String email) {
this.email = email == null ? null : email.trim();
}
/**
* This method was generated by MyBatis Generator.
* This method returns the value of the database column tbl_employee.gender
*
* @return the value of tbl_employee.gender
*
* @mbg.generated
*/
public String getGender() {
return gender;
}
/**
* This method was generated by MyBatis Generator.
* This method sets the value of the database column tbl_employee.gender
*
* @param gender the value for tbl_employee.gender
*
* @mbg.generated
*/
public void setGender(String gender) {
this.gender = gender == null ? null : gender.trim();
}
/**
* This method was generated by MyBatis Generator.
* This method returns the value of the database column tbl_employee.d_id
*
* @return the value of tbl_employee.d_id
*
* @mbg.generated
*/
public Integer getdId() {
return dId;
}
/**
* This method was generated by MyBatis Generator.
* This method sets the value of the database column tbl_employee.d_id
*
* @param dId the value for tbl_employee.d_id
*
* @mbg.generated
*/
public void setdId(Integer dId) {
this.dId = dId;
}
}
6.重新再xml配置文件中定义映射
<resultMap id="MyDifEmp" type="com.springboot.dao.entity.Employee">
<id column="id" property="id"/>
<result column="last_name" property="lastName"/>
<result column="gender" property="gender"/>
<result column="d_id" property="dId" />
<result column="did" property="dept.id"/>
<result column="dept_name" property="dept.departmentName"/>
</resultMap>
<select id="selectEmployee" resultMap="MyDifEmp">
SELECT e.id id,e.last_name last_name,e.email email,e.gender gender,e.d_id d_id,
d.id did,d.dept_name dept_name FROM tbl_employee e,tbl_dept d
WHERE e.d_id=d.id AND e.id=#{id}
</select>
代码就写完了，我们启动一下。
这里用postman测试一下：
大功告成！！！！！！！！！！！！！