add a dynamic column to an entity without saving it to the table

I have a model class like the following:

package com.example.model;
import java.util.Map;

import javax.persistence.Column;
import javax.persistence.Convert;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Table;

import com.example.helpers.StringMapConverter;
@Entity
@Table(name = "buildingcompanies")

public class Buildcompanies {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private int id;
    @Column(name = "shortname")
    private String shortname;
    @Column(name = "fullname")
    private String fullname;
    @Column(name = "address")
    private String address;
    @Column(name = "telephone")
    private String telephone;
    @Column(name = "website")
    private String website;
    @Column(name = "sociallinks")
      @Convert(converter = StringMapConverter.class)

    private  Map<String, String> sociallinks;
    @Column(name = "foundationyear")
    private String foundationyear;
    
    public Buildcompanies() {

    }

    public Buildcompanies(String shortname, String fullname, String address, String telephone, String website,
            Map<String, String> map, String foundationyear) {
        this.shortname = shortname;
        this.fullname = fullname;
        this.address = address;
        this.telephone = telephone;
        this.website = website;
        this.sociallinks = map;
        this.foundationyear = foundationyear;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getShortname() {
        return shortname;
    }

    public void setShortname(String shortname) {
        this.shortname = shortname;
    }

    public String getFullname() {
        return fullname;
    }

    public void setFullname(String fullname) {
        this.fullname = fullname;
    }

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    public String getTelephone() {
        return telephone;
    }

    public void setTelephone(String telephone) {
        this.telephone = telephone;
    }

    public String getWebsite() {
        return website;
    }

    public void setWebsite(String website) {
        this.website = website;
    }

    

    public Map<String, String> getSociallinks() {
        return sociallinks;
    }

    public void setSociallinks(Map<String, String> sociallinks) {
        this.sociallinks = sociallinks;
    }

    public String getFoundationyear() {
        return foundationyear;
    }

    public void setFoundationyear(String foundationyear) {
        this.foundationyear = foundationyear;
    }
    
    
    
    
    
    
}

And the method in a controller to show the output:

public ResponseEntity<List<Buildcompanies>> getAllCompanies(@RequestParam(required = false) String name) {
      try {
        List<Buildcompanies> companies = new ArrayList<Buildcompanies>();
        int test=0;
        if (name == null)
        {
            buildcompaniesRepository.findAll().forEach(companies::add);
            
        }
        else
          buildcompaniesRepository.findByShortnameContaining(name).forEach(companies::add);

        if (companies.isEmpty()) {
          return new ResponseEntity<>(HttpStatus.NO_CONTENT);
        }

        return new ResponseEntity<>(companies, HttpStatus.OK);
      } catch (Exception e) {
        return new ResponseEntity<>(null, HttpStatus.INTERNAL_SERVER_ERROR);
      }
    }

It does show an output everythin is just fine:

[
    {
        "id": 81,
        "shortname": "testing",
        "fullname": "test",
        "address": "addrtest",
        "telephone": "380979379992",
        "website": "www.site.com",
        "sociallinks": {
            "facebook": "fb.com"
        },
        "foundationyear": "1991"
    }

]

And I want to calculate each companies rating while showing data to the end user. So the output should be as follows:

[
    {
        "id": 81,
        "shortname": "testing",
        "fullname": "test",
        "address": "addrtest",
        "telephone": "380979379992",
        "website": "www.site.com",
        "sociallinks": {
            "facebook": "fb.com"
        },
        "foundationyear": "1991",
"rating": "1.5"
    }
]

Is it posible to add the rating column dynamicly to the company list or I should to create rating column in database, update method for it in the controller, iterate over the findAll() results and call it each time user tryes to acces /list endpoint?

Answer

You have two options:

1. You may introduce a new attribute in the Buildcompanies class for the purpose and annotate it with @Transient. This will denote that the attribute need not be persisted in the DB and JPA won’t attempt to create a column in the table.

2. The recommended approach is to not use the Entity class as a response object. You should ideally have a domain object and the database response should be mapped to this object. While mapping you can apply whatever custom details you want to add to it.