Question

Not sure how to accomplish the date expression in the example below in the last line. A similar query fails to execute. I assume I’ll have to use some sort of Projections SqlFunction? Anyone help?

Session.QueryOver(() => myobj)
.JoinAlias(() => myobj.Object, () => o1)
.Where(() => myobj.SomeInt > o1.Date.Subtract(someTime).Minutes);

Answer 1

We need to convert your date operations from C# methods into DB Server functions. In case of MS SQL Server, we can use the DATEDIFF function:

DATEDIFF(datepart, startdate, endate)

Expecting that your object has a column Date so we can create this ICriterion

DateTime someTime = ...;
var sqlString = " DATEDIFF( mi, ?, [Date]) < {alias}.SomeInt ";
var sql = NHibernate.Criterion.Expression.Sql(sqlString
              , someTime
              , NHibernate.NHibernateUtil.DateTime);

Having this SQL statement as ICriterion we can adjust your snippet:

Session
  .QueryOver(() => myobj)
  .JoinAlias(() => myobj.Object, () => o1)
  .Where(sql); // sql = our ICriterion above

This is just a quick example… starting point how to use NHibernate API to do it… some subquery should be more suitable to avoid using explicit SomeInt column name…