具有两个以上外键的表的JPA映射

Question

Below is my database where "table_relation" is having foreign key of other 3 tables "person, address, salary"

Here are my entities for 3 main tables

Below is the Entity for "table_relation"

@Table(name="table_relation")
@Entity
public class TableRelationEntity {

    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    @Column(name="id")
    private int id;

    @JoinColumn(name="person_id", referencedColumnName="person_id")
    @ManyToOne
    private PersonEntity person;

    @JoinColumn(name="address_id", referencedColumnName="address_id")
    @ManyToOne
    private AddressEntity address;

    @JoinColumn(name="salary_id", referencedColumnName="salary_id")
    @ManyToOne
    private SalaryEntity salary;

    //getters and setters

I've written getters and setters for all properties.

I'm able to get data from the "table_relation" entity using spring data JPA in the below format

{
    id: 1,
    person: { 
        id: 4,
        name: "name 1"
    },
    address: {
        id: 1,
        city: "city 1"
    },
    salary: {
        id: 1,
        amount: "100000"
    }
}

I want to get the "Person" with list of "Address" when searched with "Salary.amount" in the below format.

{ 
    id: 4,
    name: "name 1",
    address: [
        {
            id: 1,
            city: "city 1"
        },
        {
            id: 2,
            city: "city 2"
        }
    ]
}

Can this be achieved by using Mappings in the Provider and Address Entities? Please guide me in achieving this. This is replication of my original problem but not the problem itself.

Any help is greatly appreciated.

Thanks in advance.

Answer 1

First off, your database design is not in normal form. You are now repeating a persons salary for each of the persons addresses. What you should have is two join-tables, one between person and salary, and one between person and address. Or even better, as none of the relationships are many-many, use a join column.

Second, when using JPA, you have to model based on objects, not database tables. A person has a salary, the relationship between a person and its salary is not a concrete "thing".

Your person-entity should look something like this:

@Entity
public class Person {
    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    @Column(name="id")
    private int id;

    @OneToMany(cascade = CascadeType.ALL, orphanRemoval = true)
    @JoinColumn(name = "person_id")
    private List<Address> adresses = new ArrayList<>();

    @ManyToOne(cascade = CascadeType.ALL)
    @JoinColumn(name = "salary_id")
    private Salary salary;

    //setters, getters, etc
}

Entities for address and salary need not change.

As for tables, you should have:

Person(id, name, salary_id)
Address(id, city, person_id)
Salary(id, amount)