NHibernate Projection queries group by date

Question

I want to write a Projection query in NHibernate that groups records by date and counts "Tax" field value for those records. My question is that the database has the value as DateTime, how will I group records just by date and not time.Below is my code

template.Criteria.SetProjection(
                Projections.ProjectionList()
                .Add(Projections.GroupProperty("IssueDatetime"), "DateVal")
                .Add(Projections.Sum("Tax"), "TotalFare")
            );

The database stores the IssueDatetime field as DateTime type. I want to count the Tax per date and ignore the time part. Can anybody help me out with the above requirement?

Answer 1

Use the following for the first projection:

Projections.GroupProperty(
    Projections.SqlFunction("date",
                            NHibernateUtil.Date,
                            Projections.GroupProperty("IssueDateTime")))

For NH 2.x:

Projections.GroupProperty(
    Projections.SqlFunction(new SQLFunctionTemplate(
                                NHibernateUtil.Date,
                                "dateadd(dd, 0, datediff(dd, 0, ?1))"),
                            NHibernateUtil.Date,
                            Projections.GroupProperty("IssueDateTime")))

Answer 2

Assuming SQL Server and T-SQL, this ICriteria will do it.

IList results = Session.CreateCriteria(typeof(Record), "record")
    .SetProjection(Projections.ProjectionList()
        .Add(Projections.SqlGroupProjection("CONVERT(date, {alias}.[IssueDatetime]) AS [DateVal]", "CONVERT(date, {alias}.[IssueDatetime])", new[] { "DateVal" }, new IType[] { NHibernateUtil.Date }))
        .Add(Projections.Sum("Tax"), "TotalFare"))
    .List();

The following SQL is generated.

SELECT CONVERT(date, this_.[IssueDatetime]) AS [DateVal], sum(this_.Tax) as y1_ FROM IgnoreTime_Record this_ GROUP BY CONVERT(date, this_.[IssueDatetime])