What about findByExample in JPA book?

[Varun Chopra]

Hi Mike and Merrick

Does your book suggest how to achieve findByExample in JPA?
For e.g. if I have an object with 4 instance variables, I fill random 2 of them and try to search. Is it suggested in JPA2 book?

regards
Varun

[Mark Spritzler]

JPA2 spec now has the ability to create a Criteria query, which allows you to do query by example.

Mark

[Mike Keith]

I'm sorry to say that we didn't actually get to do QBE in JPA 2.0. Criteria API does not have any special operators for it so entity equality is just like in JP QL, based on PK value. Sorry, but hopefully we'll be more successful on that front in the next go-round. For now it is one of those vendor features that every vendor supports, but is not in the spec yet.

[Mark Spritzler]

Mike Keith wrote:I'm sorry to say that we didn't actually get to do QBE in JPA 2.0. Criteria API does not have any special operators for it so entity equality is just like in JP QL, based on PK value. Sorry, but hopefully we'll be more successful on that front in the next go-round. For now it is one of those vendor features that every vendor supports, but is not in the spec yet.

Really, I kind of assumed if there was a Criteria object here was QBE. ;)

Mark

[Varun Chopra]

Mike Keith wrote:I'm sorry to say that we didn't actually get to do QBE in JPA 2.0. Criteria API does not have any special operators for it so entity equality is just like in JP QL, based on PK value. Sorry, but hopefully we'll be more successful on that front in the next go-round. For now it is one of those vendor features that every vendor supports, but is not in the spec yet.

Ok, well I think you can give sample code for QBE in JPA 2.0 on web-page dedicated for the book. I am sure this feature comes among the most sought after ones in ORM community.

[Mike Keith]

We have tried to keep the book focused on the specification. Since this is a vendor feature then vendor documentation will generally cover this. If you really want a code example that uses QBE, though, here is a sample of using it in the EclipseLink JPA 2.0 reference implementation:

// Create a native EclipseLink query using QBE policy
QueryByExamplePolicy policy = new QueryByExamplePolicy();
policy.excludeDefaultPrimitiveValues();
ReadObjectQuery q = new ReadObjectQuery(sampleEmployee, policy);

// Wrap the native query in a standard JPA Query and execute it
Query query = JpaHelper.createQuery(q, em);
return query.getSingleResult();

[Varun Chopra]

Mike Keith wrote:We have tried to keep the book focused on the specification. Since this is a vendor feature then vendor documentation will generally cover this. If you really want a code example that uses QBE, though, here is a sample of using it in the EclipseLink JPA 2.0 reference implementation:

// Create a native EclipseLink query using QBE policy
QueryByExamplePolicy policy = new QueryByExamplePolicy();
policy.excludeDefaultPrimitiveValues();
ReadObjectQuery q = new ReadObjectQuery(sampleEmployee, policy);

// Wrap the native query in a standard JPA Query and execute it
Query query = JpaHelper.createQuery(q, em);
return query.getSingleResult();

Thanks for the code. It looks like there's no vendor neutral way to achieve it.