NHibernate ORDER BY CURRENT_TIMESTAMP conflicts with DISTINCT - sql-server

Question

Could anybody please explain why NHibernate on MsSql2012Dialect generates query that can not be processed by server? It builds query this way when there is no sorting specified explicitly.
...
ORDER BY CURRENT_TIMESTAMP
OFFSET 0 ROWS FETCH FIRST 10 ROWS ONLY

Answer 1

This is unresolved bug registered in jira, based on the suggestions, this is my work around:
public class MyMsSql2012Dialect : MsSql2012Dialect
{
public override SqlString GetLimitString(SqlString querySqlString, SqlString offset, SqlString limit)
{
var result = base.GetLimitString(querySqlString, offset, limit);
return result.Replace("ORDER BY CURRENT_TIMESTAMP", "ORDER BY 1");
}
}

Answer 2

As you said in the question, following query is generated if no ORDER BY is explicitly specified:
SELECT
distinct this_.ColumnName as y0_
FROM
[DB].[dbo].Table this_
ORDER BY
CURRENT_TIMESTAMP OFFSET 0 ROWS FETCH FIRST 10 ROWS ONLY;
Error is:
ORDER BY items must appear in the select list if SELECT DISTINCT is specified.
Error only occur if BOTH Projections.Distinct and Take(1) is provided and SQL Server version is above 2012 (Dialect is MsSql2012Dialect or above).
The better solution is to provide the ORDER BY column to NHibernate explicitly and include that column in SELECT list.
Session.QueryOver<Entity>()
.Select(
Projections.Distinct(Projections.Property<Entity>(x => x.ColumnName))
)
.Where(....)
.OrderBy(Projections.Property<Entity>(x => x.ColumnName)).Asc()
.Take(1);