Can any tell me , any guidelines, in which schenario we should use HQL , Query by Criteria , Query by example?

Basically I am looking for some guidelines or tips for using HQL , Query by Criteria , Query by example while retrieval of data from database.

Sudhir

Use HQL when you know the exact shape of the query. For example, if you were implementing a method like "findPersistedObjectByDate(Date d);".

Use normal Criteria when you don't know the exact shape of the query. For example, when your query is being built from user-entered values, where some values are optional.

Use query-by-example Criteria as a shortcut for normal Criteria when you have a similar object. It's also useful if your query is simple but you don't have access to hibernate classes in the place you're building the query. For example, in a webapp action class, you mightn't be allowed (because of company policy) to use hibernate DetachedCriteria. So you could build an object with the user-entered search criteria, and pass that down through your business logic to your data access layer, and that does the search by example.

Thanks for the tips....but could you please also provide me with few justifications also for individual approach....

Thanks a lot in advance

sudhir h

These are just personal opinions:

If you can't think of a good reason to use Criteria, then use HQL. It should be your first choice most of the time, as once you have the query working, there are fewer things that can go wrong. It's also the most powerful, as there are some things that Critieria just can't do (e.g. theta-style joins).

If you need to allow searching from a part of your code that isn't allowed use Hibernate classes, consider using query by example. All you have to do is instantiate an object and fill in a few "example" values, then pass it down to a part of your code that does use Hibernate.

Otherwise, use Crtieria.

All the points mentioned in this thread are excellent. Here are my thoughts:

Some of my colleagues and I have adopted the approach of using the ICriteria interface when possible. We like having a bit of compile-time error checking for our queries and find that in some cases, we can factor common criteria into separate methods.

As mentioned, HQL is more expressive. Thus, we try to model our queries using ICriteria and fall back to HQL when appropriate. Most of our queries are fairly straight forward, with the exception of some that use GROUP BY commands.