JPA - How to create entities where EntityA saves list ids of another table - spring-boot

Question

I have an EntityA , and EntityB.
EntityB is a master table.
EntityA can have multiple id's of Entity B. So A column of EntityA should hold list/set of ids of EntityB.
I should be able to query EntityA, to get list of Ids of EntityB.
Note: Many rows in EntityA can refer to same id of EntityB
I tried below, but it I don't see column
#OneToMany(mappedBy = "todo")
private List<ObjectStore> store = new ArrayList<>();
Please can I ask how to do this using Spring JPA.
EDIT:
#Entity
public class Dept {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
#NotNull(message = "name is mandatory")
private String name;
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
and
#Entity
public class Employee {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
#NotNull(message = "name is mandatory")
private String name;
#ElementCollection(targetClass=String.class)
#CollectionTable(name = "DEPT", joinColumns = #JoinColumn(name="id"))
private List<String> dept = new ArrayList<String>(4);
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
I observed that DEPT column got added to dept table. This is unwanted.
Use Case: Employee can hold list of departments. Many employee records, should be able to have same dept references.

Answer 1

You should change table name from "DEPT". Because #CollectionTable will create another embedded table with given name. In you case dept is already there so it will create new column in Dept.
// Employee Class
#ElementCollection(targetClass=String.class)
#CollectionTable(name = "DEPT_EMPLOYEE_MAPPING", joinColumns = #JoinColumn(name="Employee_id"))
#MapKeyJoinColumn(name="Dept_Id")
private Map<Dept,DeptEmployeeRelationData> depts;
//Dept class
#ElementCollection
#CollectionTable(name="DEPT_EMPLOYEE_MAPPING",joinColumns=#JoinColumn(name="Dept_Id"))
#MapKeyJoinColumn(name="Employee_Id")
Map<Employee, DeptEmployeeRelationData> employees;
#Embeddable
class DeptemployeeRelationData {
#Column(name="createdAt")
DateTime createdAt;
}
Your mapping is many to many.
Hope this will work!

Answer 2

I used
#ManyToMany
#OrderColumn
private List<String> dept = new ArrayList<String>(4);
and working as per my requirement
DEPT, EMPLOYEE , EMPLOYEE_DEPT created