Question

Given the model Activity containing a bag with models of type Report (one to many). I would like to get a list of all activities, containing the number of reports of each activity. This two queries don’t lead to any good, the counter is always 1 (which is wrong):

select act, (select count(r) from act.Reports r) from Activity act

Or:

select act, count( elements(act.Reports) ) from Activity act group by act.ActivityId, act.Title

Is it possible to write a proper query in HQL to solve this easy task?

Thx for any tipps!
sl3dg3

Edit:
Following the mappings. Activity:

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2">
    <class
        name="Core.Models.Config.Activity, Core"
        table="Activity"
    >

        <!-- primary key -->
        <id name="ActivityId" type="Int32" unsaved-value="0" access="property">
            <column name="ActivityId" not-null="true"/>
            <generator class="identity" />
        </id>

        <!-- Properties -->
        <many-to-one name="Title" fetch="join" cascade="all"/>

        <!-- One-To-Many Reports -->
        <bag name="Reports" inverse="true" fetch="join">
            <key column="ReportId" />
            <one-to-many class="Core.Models.Report"/>
        </bag>

    </class>
</hibernate-mapping>

Mapping Report:

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2">
    <class
        name="Core.Models.Report, Core"
        table="Report"
    >

    <!-- primary key -->
    <id name="ReportId" type="Int32" unsaved-value="0" access="property">
        <column name="ReportId" not-null="true"/>
        <generator class="identity" />
    </id>

    <!-- Properties (shortened - there are more many-to-one and one bag -->
    <property name="Created" />
    <many-to-one name="Activity" column="ActivityId" />

</class>

Class Activity:

public class Activity
{

    public Activity()
    {
        Title = new Translation();
    }

    public virtual int ActivityId { get; set; }

    public virtual Translation Title { get; set; }

    public virtual IList<Report> Reports { get; set; }
}

Class Report:

public class Report
{

    /// <summary>
    /// HNIBERNATE ONLY
    /// </summary>
    public Report() 
    { }

    /// <summary>
    /// Init Report
    /// </summary>
    public Report(User author)
    {
        // ... Shortened
        Activity = new Activity();
    }

    public virtual Activity Activity { get; set; }

}

Answer 1

Your first HQL query has the wrong syntax. Try this instead:

select act, (select count(*) from act.Reports) from Activity act

Your second HQL query cannot work, because you would need all the columns in the GROUP BY clause. Try this instead:

select act.ActivityId, act.Title, count( elements(act.Reports) ) 
from Activity act 
group by act.ActivityId, act.Title

Edit:

Ah, I think this might be the bug:

<bag name="Reports" inverse="true" fetch="join">
    <key column="ActivityId" /> <-- instead of ReportId
    <one-to-many class="Core.Models.Report"/>
</bag>