[hibernate-issues] [Hibernate-JIRA] Created: (HHH-2143) Add support for projection to the Query API as in the Criteria API to ease automated pagination of HQL queries

[Cédric Vidal (JIRA)]

Add support for projection to the Query API as in the Criteria API to ease automated pagination of HQL queries
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         Key: HHH-2143
         URL: http://opensource.atlassian.com/projects/hibernate/browse/HHH-2143
     Project: Hibernate3
        Type: Improvement

  Components: query-hql  
    Reporter: Cédric Vidal


Today, both the Criteria and Query APIs have setMaxResults and setFirstResult methods. Thanx to these methods, it is really easy to add pagination to an existing Criteria or Query in technical code in order to remove that consideration from user code.

But, most of the time, it is also necessary to display the total number of records or the number of pages which either way requires to fetch the total number of records which would be returned by the query. The Criteria API introduced the setProjection(Projection) method which elegantly enables to do just that:

// User code
Criteria existingCriteria = session.createCriteria(Cat.class);

// Technical Pagination code
Integer count = (Integer)existingCriteria
    .setProjection( Projections.rowCount() )
    .uniqueResult();

The problem is that the Query API lacks the setProjection method. Today, with an HQL query, one has to manually write in user code the additional count(*) specific query that returns the total number of results.

It would be very usefull as well as time saving to be able to do the same as in the Query API:

// User code
Query existingQuery = session.createQuery("from Cat")

// Technical Pagination code
Integer count = (Integer)existingQuery
    .setProjection( Projections.rowCount() )
    .uniqueResult();

Regards,

Cédric Vidal


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