How does one make NHibernate stop using nvarchar(4000) for insert parameter strings?

Question

I need to optimize a query that is being produced by a save (insert query) on a domain entity. I've configured NHibernate using Fluent NHibernate.

Here's the query generated by NHibernate during the insertion of a user's response to a poll:

exec sp_executesql N'INSERT INTO dbo.Response (ModifiedDate, IpAddress, CountryCode, 
IsRemoteAddr, PollId) VALUES (@p0, @p1, @p2, @p3, @p4); select SCOPE_IDENTITY()',N'@p0
datetime,@p1 nvarchar(4000),@p2 nvarchar(4000),@p3 bit,@p4 int',
@p0='2001-07-08 03:59:05',@p1=N'127.0.0.1',@p2=N'US',@p3=1,@p4=2

If one looks at the input parameters for IpAddress and CountryCode, one will notice that NHibernate is using nvarchar(4000). The problem is that nvarchar(4000) is far larger than I need for either IpAddress or CountryCode and due to high traffic and hosting requirements I need to optimize the database for memory usage.

Here's the Fluent NHibernate auto-mapping overrides for those columns:

    mapping.Map(x => x.IpAddress).CustomSqlType("varchar(15)");
    mapping.Map(x => x.CountryCode).CustomSqlType("varchar(6)");

This isn't the only place that I see unnecessary nvarchar(4000)'s popping up.

How do I control NHibernate's usage of nvarchar(4000) for string representation?

How do I change this insert statement to use the proper sized input parameters?

Answer 1

Specify the Type as NHibernateUtil.AnsiString with a Length instead of using a CustomSqlType.