Mapping Multiple Columns to same field of an Object which is part of an Array JPA

Question

I am trying to map an array of Objects to a field. All the fields in that object are being mapped to columns with different name but similar structure. The response structure should be:

 "customers": [
    {
      "firstName": "string",
      "lastName": "string",
      "products": [
        {
            "description":"string",
            "amount": "string"
        },
        {
            "description":"string",
            "amount": "string"
        }
      ]
    }
 ]

Inside the products field, I have a list of product(description and amount). In DB, columns are stored like

product_des1,product_amt1,product_des2,product_amt2.....product_des30,product_amt30

. I need to map these two fields to the product(object). How should I approach to solve the problem using JPA annotations if possible?

For the reference: Customers.class

@Entity
public class Customers implements Serializable {

    @Column(name = "firstName")
    private String firstName;

    @Column(name = "lastName")
    private String lastName;

    @ElementCollection
    List<Products> products;

}

Product.class

@Embeddable
public class Product implements Serializable {

    @Column(?)
    private String description;

    @Column(?)
    private String amount;

}

@Zorglube I checked but did'nt find anything specific to this scenario. — Pramay Nikhade
– Pramay Nikhade, Commented Nov 15, 2019 at 11:28
So you have 1 table for both entities? And you can have a max of 30 products? — XtremeBaumer
– XtremeBaumer, Commented Nov 15, 2019 at 11:34
I would start by hunting down whoever designed the database. — Alan Hay
– Alan Hay, Commented Nov 15, 2019 at 13:13
In that case, Smutje's answer is the way to go. Though it would probably make more sense to redesign the database and set up a proper @ManyToMany relationship. This is currently not possible — XtremeBaumer
– XtremeBaumer, Commented Nov 15, 2019 at 13:56

Community · Accepted Answer · 2020-06-20 09:12:55Z

1

Inside the products field, I have a list of product(description and amount). In DB, columns are stored like

product_des1,product_amt1,product_des2,product_amt2.....product_des30,product_amt30

So your Products JPA entity should simply look like this:

@Embeddable
public class Products implements Serializable {

    @Column(name = "product_des1")
    private String description1;

    @Column(name = "product_amt1")
    private String amount1;

    @Column(name = "product_des2")
    private String description2;

    @Column(name = "product_amt2")
    private String amount2;

   // ... repeat
}

if you don't want to do additional mapping between the DB and JPA entities (which I don't recommend - I try to keep JPA entities as exact representation of a DB row and map, if necessary, in Java and not between different technologies).

edited Jun 20, 2020 at 9:12

CommunityBot

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answered Nov 15, 2019 at 11:38

Smutje

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3 Comments

Pramay Nikhade Over a year ago

But using this way I'll be having several fields, it should be "description" and "amount". Moreover is it advisable to solve it programatically?

Smutje Over a year ago

I strongly recommend to keep the database and the JPA entities equal, i.e. let the JPA entities reflect the DB 1:1 because having both a different technology (database vs. Java class) and representation (DB structure vs. object representation) is a guaranteed way to confusion and less maintainability because you have to keep multiple things in order when changing one or the other. I don't see any problem in having a proper object with a list of products as the "business" representation of your application and would do a mapping between both in a service, or simply adjust the database.

Pramay Nikhade Over a year ago

Oh okay , I'll try to keep my products class as suggested by you then later I'll manipulate while sending the response.

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