What are the pros and cons of using Criteria or HQL? The Criteria API is a nice object-oriented way to express queries in Hibernate, but sometimes Criteria Queries are more difficult to understand/build than HQL.
When do you use Criteria and when HQL? What do you prefer in which use cases? Or is it just a matter of taste?
I mostly prefer Criteria Queries for dynamic queries. For example it is much easier to add some ordering dynamically or leave some parts (eg restrictions) out depending on some parameter.
On the other hand I'm using HQL for static and complex queries, because it's much easier to understand/read HQL. Also, HQL is a bit more powerful, I think, eg for different join types.
There is a difference in terms of performance between HQL and criteriaQuery, everytime you fire a query using criteriaQuery, it creates a new alias for the table name which does not reflect in the last queried cache for any DB. This leads to an overhead of compiling the generated SQL, taking more time to execute.
Regarding fetching strategies [http://www.hibernate.org/315.html]
Criteria respects the laziness settings in your mappings and guarantees that what you want loaded is loaded. This means one Criteria query might result in several SQL immediate SELECT statements to fetch the subgraph with all non-lazy mapped associations and collections. If you want to change the "how" and even the "what", use setFetchMode() to enable or disable outer join fetching for a particular collection or association. Criteria queries also completely respect the fetching strategy (join vs select vs subselect). HQL respects the laziness settings in your mappings and guarantees that what you want loaded is loaded. This means one HQL query might result in several SQL immediate SELECT statements to fetch the subgraph with all non-lazy mapped associations and collections. If you want to change the "how" and even the "what", use LEFT JOIN FETCH to enable outer-join fetching for a particular collection or nullable many-to-one or one-to-one association, or JOIN FETCH to enable inner join fetching for a non-nullable many-to-one or one-to-one association. HQL queries do not respect any fetch="join" defined in the mapping document.
Criteria is an object-oriented API, while HQL means string concatenation. That means all of the benefits of object-orientedness apply:
All else being equal, the OO version is somewhat less prone to error. Any old string could get appended into the HQL query, whereas only valid Criteria objects can make it into a Criteria tree. Effectively, the Criteria classes are more constrained. With auto-complete, the OO is more discoverable (and thus easier to use, for me at least). You don't necessarily need to remember which parts of the query go where; the IDE can help you You also don't need to remember the particulars of the syntax (like which symbols go where). All you need to know is how to call methods and create objects. Since HQL is very much like SQL (which most devs know very well already) then these "don't have to remember" arguments don't carry as much weight. If HQL was more different, then this would be more importatnt.
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