Retrive a object of parent class into child class in spring boot application - spring

Question

I am building REST API using spring boot application. I have connected application to Mongodb database. I have created a database named "Employee" and collection as "Employee" itself. Now i want to create a document. I have three class. Class A, Class B and class C.
Class A is the parent Class having property (id,name,password). Class B is child class and extends Class A with property(address,phoneNumber) and class C is child class which also extends class A with property (fatherName,MotherName).
Now i want to add the data to database as object of B or object of C and also want to retrive the data from database as object of B or Object of C.
here is code of Class A:
package com.example.webproject;
import org.springframework.data.annotation.Id;
import org.springframework.data.mongodb.core.mapping.Document;
#Document(collection="Employee")
public class A {
#Id
private String id;
private String passwd;
private String username;
public String getId() {
return id;
}
public void setIp(String string) {
this.ip = string;
}
public String getPasswd() {
return passwd;
}
public void setPasswd(String passwd) {
this.passwd = passwd;
}
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
class B:
package com.example.webproject;
public class B extends A {
private String address;
private String phoneNumber;
public String getAddress() {
return address;
}
public void setAddress(String address) {
this.address = address;
}
public String getPhoneNumber() {
return phoneNumber;
}
public void setPhoneNumber(String phoneNumber) {
this.phoneNumber= phoneNumber;
}
}
Class C :
package com.example.webproject;
public class C extends A {
private String fatherName;
private String motherName;
public String getFatherName() {
return fatherName;
}
public void setFatherName(String fatherName) {
this.fatherName = fatherName;
}
public String getMotherName() {
return motherName;
}
public void setMotherName(String motherName) {
this.motherName = motherName;
}
}
EmployeeRepository.java
package com.example.webproject;
import org.springframework.data.mongodb.repository.MongoRepository;
import org.springframework.stereotype.Repository;
#Repository
public interface EmployeeRepository extends MongoRepository<A,String> {}
EmployeeController.java
#RestController
public class EmployeeController {
#Autowired
private EmployeeRepository repo;
#PostMapping("/addByB")
public String addDataByB(#RequestBody B res) {
repo.save(res);
return "added";
}
#PostMapping("/addByC")
public String addDataByC(#RequestBody C res) {
repo.save(res);
return "added";
}
#GetMapping("/getByB")
public List<B> getDataByB(){
List<B> b= repo.findAll(); #Here it throws error because repo.findAll return object of A.
return b;
}
When i try to add data as B object or C object using swagger , the data is getting stored in database. Now i want to retrieve the data as B object or C object, how to achieve this?

Answer 1

Because you just create Repository of class A and call it, you nedd to creat two another repo of class B and C then call them like you call " EmployeeRepository " so you can use them and get the data.