NHibernate QueryOver group by without selecting the grouped by column

Question

Having a query like the following:

var subquery = SessionFactory.GetCurrentSession()
    .QueryOver()
    .Where(_ => _.SomeOtherEntity.         


        

Answer 1

You can do it with your own projection, which is similar to NHibernate ProjectionList with slightly different implementation of ToSqlString, GetTypes and GetTypedValues methods.

public static class CustomProjections
{
    public static ProjectionWithGroupByWithoutSelectProjection GroupByWithoutSelect(IProjection projection, params Expression>[] groupByExpressions)
    {
        var projectionRet = new ProjectionWithGroupByWithoutSelectProjection();
        projectionRet.Add(projection);
        foreach (var groupByExpression in groupByExpressions)
        {
            projectionRet.Add(Projections.Group(groupByExpression));
        }

        return projectionRet;
    }
}

public class ProjectionWithGroupByWithoutSelectProjection : IProjection
{
    // because ProjectionList constructor is protected internal
    private class ProjectionListCustom : ProjectionList
    {
    }

    private readonly ProjectionList _projectionList = new ProjectionListCustom();

    protected internal ProjectionWithGroupByWithoutSelectProjection()
    {
    }

    public ProjectionWithGroupByWithoutSelectProjection Add(IProjection proj)
    {
        _projectionList.Add(proj);
        return this;
    }

    public ProjectionWithGroupByWithoutSelectProjection Add(IProjection projection, string alias)
    {
        _projectionList.Add(projection, alias);
        return this;
    }

    public ProjectionWithGroupByWithoutSelectProjection Add(IProjection projection, Expression> alias)
    {
        _projectionList.Add(projection, alias);
        return this;
    }

    public IType[] GetTypes(ICriteria criteria, ICriteriaQuery criteriaQuery)
    {
        return _projectionList[0].GetTypes(criteria, criteriaQuery);
    }

    public SqlString ToSqlString(ICriteria criteria, int loc, ICriteriaQuery criteriaQuery, IDictionary enabledFilters)
    {
        return _projectionList[0].ToSqlString(criteria, loc, criteriaQuery, enabledFilters);
    }

    public SqlString ToGroupSqlString(ICriteria criteria, ICriteriaQuery criteriaQuery, IDictionary enabledFilters)
    {
        return _projectionList.ToGroupSqlString(criteria, criteriaQuery, enabledFilters);
    }

    public string[] GetColumnAliases(int position, ICriteria criteria, ICriteriaQuery criteriaQuery)
    {
        return _projectionList.GetColumnAliases(position, criteria, criteriaQuery);
    }

    public string[] GetColumnAliases(string alias, int position, ICriteria criteria, ICriteriaQuery criteriaQuery)
    {
        return _projectionList.GetColumnAliases(alias, position, criteria, criteriaQuery);
    }

    public IType[] GetTypes(string alias, ICriteria criteria, ICriteriaQuery criteriaQuery)
    {
        return _projectionList[0].GetTypes(alias, criteria, criteriaQuery);
    }

    public string[] Aliases => _projectionList.Aliases;

    public override string ToString()
    {
        return _projectionList.ToString();
    }

    public bool IsGrouped => _projectionList.IsGrouped;

    public bool IsAggregate => _projectionList.IsAggregate;

    public TypedValue[] GetTypedValues(ICriteria criteria, ICriteriaQuery criteriaQuery)
    {
        return _projectionList[0].GetTypedValues(criteria, criteriaQuery);
    }
}