Hibernate HQL: Get count of results without actually returning them

Question

I want to get the count of the results of a dynamically-generated HQL query, without actually getting the list of results. Say that the query I have is something like:

select Company company LEFT OUTER JOIN FETCH products product

I read in the Hibernate documentation that:

You can count the number of query results without returning them:

( (Integer) session.createQuery("select count(*) from ....").iterate().next() ).intValue()

I suspected that I should be replacing the .... with my query, but that does not work, as HQL does not support sub-selects in FROM.

So, how should I count the results of a dynamically generated HQL query? I think that by executing it and getting the .size() of the results list may be unnecessary overhead.

Cheers!

*UPDATE: *

I used this regex to convert my query:

Number num = (Number) em.createQuery(dynamicQuery.replaceAll("select \\w+ from ", "select count(*) from ")).getSingleResult();

And I get this:

Blockquote

EJB Exception: ; nested exception is: java.lang.IllegalArgumentException: org.hibernate.QueryException: query specified join fetching, but the owner of the fetched association was not present in the select list [FromElement{explicit,not a collection join,fetch join,fetch non-lazy properties,classAlias=product,role=org.myCompany.applicant.entity.Applicant.products,tableName=PRS_DEV.PRODUCT,tableAlias=products1_,origin=PRS_DEV.APPLICANT applicant0_,colums={applicant0_.APPLICANT_ID ,className=org.myCompany.product.entity.Product}}] [select count(*) from org.myCompany.applicant.entity.Applicant applicant LEFT OUTER JOIN FETCH applicant.products product ]; nested exception is: java.lang.IllegalArgumentException: org.hibernate.QueryException: query specified join fetching, but the owner of the fetched association was not present in the select list [FromElement{explicit,not a collection join,fetch join,fetch non-lazy properties,classAlias=product,role=org.myCompany.applicant.entity.Applicant.products,tableName=PRS_DEV.PRODUCT,tableAlias=products1_,origin=PRS_DEV.APPLICANT applicant0_,colums={applicant0_.APPLICANT_ID ,className=org.myCompany.product.entity.Product}}] [select count(*) from org.myCompany.applicant.entity.Applicant applicant LEFT OUTER JOIN FETCH applicant.products product ]

Answer 1

This should do the trick:

select count(*) FROM Company c JOIN ...

There is no sub-select involved, just instead of returning Company, you return the count.

Edit: The FETCH is out of place now. You're not returning the entities from the query, but only the count, thus, Hibernate complains. Removing it should help:

select count(product) from org.myCompany.applicant.entity.Applicant applicant 
    LEFT OUTER JOIN applicant.products product