Specifying an index (non unique key) using JPA

Question

How do you define a field, ie email as having an index using JPA annotations. We need a non-unique key on email because there are literally millions of queries on this field per day, and its a bit slow without the key.

@Entity
@Table(name="person", 
       uniqueConstraints=@UniqueConstraint(columnNames={"code", "uid"}))
public class Person {
    // Unique on code and uid
    public String code;
    public String uid;

    public String username;
    public String name;
    public String email;
}

I have seen a hibernate specific annotation but I am trying to avoid vendor specific solutions as we are still deciding between hibernate and datanucleus.

Answer 1

As fas as I know, there isn't a cross-JPA-Provider way to specify indexes. However, you can always create them by hand directly in the database, most DBs will pick them up automatically during query planning.

Answer 2

It's not possible to do that using JPA annotation. And this make sense: where a UniqueConstraint clearly define a business rules, an index is just a way to make search faster. So this should really be done by a DBA.

Answer 3

I'd really like to be able to specify database indexes in a standardized way but, sadly, this is not part of the JPA specification (maybe because DDL generation support is not required by the JPA specification, which is a kind of road block for such a feature).

So you'll have to rely on a provider specific extension for that. Hibernate, OpenJPA clearly do offer such an extension. I can't confirm for DataNucleus but since indexes definition is part of JDO, I guess it does.

I really hope index support will get standardized in next versions of the specification and thus somehow disagree with other answers, I don't see any good reason to not include such a thing in JPA (especially since the database is not always under your control) for optimal DDL generation support.

By the way, I suggest downloading the JPA 2.0 spec.