CODEWITHSUNDEEP
javahibernatehibernate-mapping
Oleksandr_DJ
Oleksandr_DJ

Reputation: 1515

The better solution to extend DTO object (Java, Hibernate)

I use EmailAlert bean as DTO to get data by means of Hibernate. So, my class contains only fields that I have in DB. But in some cases I need additional fields to be in EmailAlert to hold intermediate data. For example "caption" field - will be calculated on java side depends of user locale, time, etc.

So, I have some variants to solve this issue.

  1. Add additional property (ex: caption) to EmailAlert bean, but do not map it with any field of DB table. Drawback: In this case we have to do not use "caption" property in hashCode() and equals() because as:

    • It really don't have a matter - field holds only intermediate data
    • I am not sure it not be a cause of problem with cache and Hibernate itself.
      I think it is very ugly to have a property of class but do not use it in equals() and hashCode() methods.
      Someone can be confusing in the future with this logic.

  2. Extend EmailAlert as EmailAlertExt with adding of "caption" property. And constructor that takes EmailAlert as argument.
    But in this case I am not sure underwater stones in case I will store EmailAlert as EmailAlertExt bean again into DB.

  3. Extend EmailAlert as EmailAlertExt2 with adding of "caption" property and take a refference to the original object. In this case EmailAlertExt2 will behave as original EmailAlert, but with additional property we need. In case we save EmailAlert we could call getOriginalValue() of EmailAlertExt2 that will return refference to original object. Drawback: too many coding :)

Guys, which of these solutions is better? May be someone have other proposals?

Upvotes: 0

Views: 3964

Answers (3)

Perception
Perception

Reputation: 80633

Extending a model object just because you want to separate mapped vs non-mapped fields is not a good idea. A good guideline would be to ask yourself the question "What is the difference between an EmailAlert and an EmailAlertX, and can I clearly define the situations where I would use one over the other?". If you cannot answer that question cleanly, or if you realize that you will always be using your subclass over the parent class, that is a sure sign that the parent class should be abstract or that you have too many classes.

In your particular case, it would make more sense to have both the mapped, and non-mapped properties on the same class, and to mark the non-mapped properties so that your ORM provider does not try to process them. You can do this by annotating these properties as being @Transient.

public class EmailAlert implements Serializable {
   @Id
   private Long id;

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

   @Transient
   private transient String caption;

   // Constructor, Getters/Setters, etc
}

Also, with respect to to your comment on hashcode/equals methods. You do not and should not include every property of a Java Bean in these methods. Only include those properties that are:

  • required to uniquely identify the object
  • are (fairly) guaranteed to have the same value over the lifecycle of the object

Upvotes: 1

bedane
bedane

Reputation: 1127

It sounds like the EmailAlert object you need at the moment is a business object, because of the "intermediate data" and "calculated on java side" bits.

Maybe use the EmailAlertDto object to populate the fields of the EmailAlertBusiness and store the extra caption field and the methods in the business object.

Upvotes: 0

Kanagaraj M
Kanagaraj M

Reputation: 966

Use '@Transient' it won't map to db hibernate will ignore this field

Upvotes: 2

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