JPA/Hibernate: What's better for composite primary keys, @IdClass or @EmbeddedId implementations and why? [duplicate]

This question already has answers here: 开发者_运维问答 Which annotation should I use: @IdClass or @EmbeddedId (7 answers) Closed 2 years ago.

what's better for JPA/Hibernate composite primary keys, @IdClass or @EmbeddedId implementations and why?

This is an intentionally naive question. I decided to use @EmbeddedId (for whatever reason) and I feel like I made the wrong choice. Dereferencing the embeddedId that contains the column properties is redundant and quite error-prone when coding.

Are there any more reasons for and/or against the other? Is the a recommendation by the JPA (spec)?

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First, if possible, avoid composite ids at all costs. But if you really need, I would recommend @EmbeddedId.

@IdClass is basically a leftover from EJB 2.1 times to make it easier from migrating from BMP. In some other rare corner cases it may be better than @EmbeddedId too. However, generally @EmbeddedId is better and more OO since it encapsulates the concept os the key much better in the object.

You may want to use @AttributeOverride(s) if you need in the key field.

I don't see why do you think that dereferencing the embedded id is redundant and error-prone.

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As Pascal wrote here's part of the answer:

Which annotation should I use: @IdClass or @EmbeddedId

In the end, I believe using @IdClass is much easier in practice, because you have to add the embeddedId property name to dereference PK properties, while these aren't written for all non-PK properties.

You always have to remember exactly which properties are part of a PK and those which are not. That complicates writing JPQL queries unneccessarily.

Also, AFAIK the JPA 2.0 spec allows you to put @Id onto @XToX/@JoinColumn/s properties and it introduces the @MapsId annotation, so that mapping identifying relationships (a.k.a. derived identifiers in JPA) are more natural to implement.

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I. Remember using idclass to do it. But I'd recommend doing everything you can to avoid multi field keys. They just create extra work.