Question

I’m creating a Restfull API Server using Spring 3.1 / Hibernate / Jackson.

I have a ‘Purchase‘ Controller/Model/Dao.

I now need to add the ability to ‘Tag‘ a purchase.

So a simple class with a ‘tagId’ and ‘tagName’ linked back to the ‘Purchase’.
A ‘Purchase’ can have many ‘Tags’, a ‘Tag’ can belong to only one ‘Purchase’.

What is the best way to represent this new ‘Tag’ class I must add? I.e.

• Should I add purchaseId attribute to ‘Tag’ model and annonate it somehow?
• Should I add a ‘Tags List’ attribuate to Purchase’ model?
• Would I create a ‘Tag’ controller that would be a subclass of ‘PurchaseController’?
• Etc…

Essentially, I’m looking for the best practice way to design this using Spring.

Additionally, any suggestions on design patterns I could employ would be welcome.
Maybe the Decorator pattern is applicable here?

All Purchases and Tags must persist to a database of course.

Thanks

Purchase Controller:

@Controller
public class PurchaseController
{

    @Autowired
    private IPurchaseService purchaseService;

    @RequestMapping(value = "purchase", method = RequestMethod.GET)
    @ResponseBody
    public final List<Purchase> getAll()
    {
        return purchaseService.getAll();
    }

    @RequestMapping(value = "purchase/{id}", method = RequestMethod.GET)
    @ResponseBody
    public final Purchase get(@PathVariable("id") final Long id)
    {
        return RestPreconditions.checkNotNull(purchaseService.getById(id));
    }

    @RequestMapping(value = "purchase/tagged", method = RequestMethod.GET)
    @ResponseBody
    public final List<Purchase> getTagged()
    {
        return RestPreconditions.checkNotNull(purchaseService.getTagged());
    }

    @RequestMapping(value = "purchase/pending", method = RequestMethod.GET)
    @ResponseBody
    public final List<Purchase> getPending()
    {
        return RestPreconditions.checkNotNull(purchaseService.getPending());
    }

    @RequestMapping(value = "purchase", method = RequestMethod.POST)
    @ResponseStatus(HttpStatus.CREATED)
    public void create(@RequestBody final Purchase entity)
    {
        RestPreconditions.checkRequestElementNotNull(entity);
        purchaseService.addPurchase(entity);
    }
}

Purchase Model:

@Entity
@XmlRootElement
public class Purchase implements Serializable
{
    /**
     * 
     */
    private static final long serialVersionUID = 6603477834338392140L;

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    private Long pan;

    public Long getId()
    {
        return id;
    }

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

    public Long getPan()
    {
        return pan;
    }

    public void setPan(Long pan)
    {
        this.pan = pan;
    }
}

Answer 1

Purchase model needs to be modified like below.

@Entity
public class Purchase implements Serializable
{
/**
 * 
 */
    private static final long serialVersionUID = 6603477834338392140L;

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    private Long pan;

    @OneToMany(mappedBy = "instance", fetch = FetchType.LAZY)
    private Set<Tag> tags;

    public Long getId()
    {
      return id;
    }

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

    public Long getPan()
    {
        return pan;
    }

    public void setPan(Long pan)
    {
        this.pan = pan;
    }

    public void setTags(Set<Tag> tags){
        this.tags = tags;
    }

    @JsonIgnore
    public Set<Tag> getTags(){
        if(tags == null){
           tags = new LinkedHashSet<Tag>();
        }
        return tags;
    }
}

and Tag model will look something like below.

@Entity
public class Tag implements Serializable{
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumns({ @JoinColumn(name = "PURCHASE__ID", referencedColumnName = "ID") })
    private Purchase purchase;

    //Other attributes, getters and setters

   @JsonIgnore
   public Purchase getPurchase(){
       return this.purchase;
   }


}

You can implement tag specific methods in PurchaseService and PurchaseController, if Purchase owns the relationship(parent) or implement separate service and controller classes for Tag.