Using SQL CONVERT function through nHibernate Criterion

Question

I have a sql view, in which the data type of every column is string, for use with the jquery datatables plugin.

One of the columns contains a uk format

Answer 1

If the setting 104 is not essential, we can get a quick solution: use CAST instead of CONVERT. This SQL Function is built-in in the NHibernate dialects:

Projections.Cast(NHibernateUtil.DateTime
               ,Projections.Property(propNames[orderByColumn]))

If the setting 104 is important we can create our own Dialect, register the CONVERT function, and use it from then ... forever

Here Andrew Whitaker nicely shows how to

• Nhibernate count distinct (based on multiple columns)

Answer 2

Based on Radim Köhler's answer, here is what I did to fix the problem:

Created a wrapper class to allow me to register the convert function and avoid the dialect exception described in my question:

public class MyDialect : MsSql2008Dialect
{
    public MyDialect()
    {
        RegisterFunction("ConvertDate", 
               new SQLFunctionTemplate(NHibernateUtil.Class, 
                                        "convert(datetime, ?1, 103)"));
    }
}

Created a custom projection class to allow me call the new function as a projection in its own right:

public static class MyProjections
{
    public static IProjection ConvertDate(params IProjection[] projections)
    {
        return Projections.SqlFunction("ConvertDate", 
                            NHibernateUtil.DateTime, projections);
    }
}

Then I check the data type that the string in column represents, then call the ConvertDate method if it is a date

 if (propTypes[orderByColumn] == typeof(DateTime))
 {
       criteria.AddOrder(orderIsDesc
           ? Order.Desc(MyProjections.ConvertDate(
                               Projections.Property(propNames[orderByColumn])))
           : Order.Asc(MyProjections.ConvertDate(
                               Projections.Property(propNames[orderByColumn]))));
 }