How to implement Mybatis federated query
This article mainly explains "how to implement Mybatis federated query". Interested friends may wish to take a look. The method introduced in this paper is simple, fast and practical. Now let the editor take you to learn "how to implement Mybatis federated query"!
Database table structure
Department
Employee
Demand one
Now the requirement is to enter id to query the corresponding employee data of the employee table, and to query the department information of the employee.
Public class Employee {private Integer id; private String lastName; private String email; private String gender; private Department dept; setter and getter.} public class Department {private Integer id; private String departmentName; setter and getter.} 1, cascading attributes encapsulate the result set implementation
This requirement obviously requires the use of two tables, and the resultMap property is needed to encapsulate department information into the dept field of the Employee object.
Method one
Select, d.id did, d.department_name from employee e, department d where e.d_id = d.id and e.id = # {id}
Method two
Select, d.id did, d.department_name from employee e, department d where e.d_id = d.id and e.id = # {id}
test
@ Test public void test1 () {SqlSession sqlSession = MyTest.getSqlSession (); EmployeeMapper mapper = sqlSession.getMapper (EmployeeMapper.class); System.out.println (mapper.getEmployee (1));}
Result
2. Step-by-step query method
DepartmentMapper.xml
Select * from department where id = # {id}
EmployeeMaper.xml
Select * from employee where id = # {id}
test
@ Test public void test1 () {SqlSession sqlSession = MyTest.getSqlSession (); EmployeeMapper mapper = sqlSession.getMapper (EmployeeMapper.class); System.out.println (mapper.getEmployee2 (1));}
Result
Requirement two
Now the requirement is to enter id to query the department information corresponding to the department table, and to query all the employee information under the department.
Public class Employee {private Integer id; private String lastName; private String email; private String gender; setter and getter.} public class Department {private Integer id; private String departmentName; private List employees; setter and getter.} 3, cascading attributes encapsulate the result set
Method
Select d.birthday, e.id eid, e.last_name, e.email, e.gender from department d left join employee e on d.id = e.d_id where d.id = # {id}
test
@ Test public void test2 () {SqlSession sqlSession = MyTest.getSqlSession (); DepartmentMapper mapper = sqlSession.getMapper (DepartmentMapper.class); System.out.println (mapper.getDepartment (1));}
Result
4. Query step by step
EmployeeMaper.xml
Select * from employee where d_id = # {did}
DepartmentMapper.xml
Select * from department where id = # {id}
test
@ Test public void test2 () {SqlSession sqlSession = MyTest.getSqlSession (); DepartmentMapper mapper = sqlSession.getMapper (DepartmentMapper.class); System.out.println (mapper.getDepartment3 (1));}
Result
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