NHibernate nvarchar/ntext truncation problem

Question

I'm using nhibernate to store some user settings for an app in a SQL Server Compact Edition table.

This is an excerpt the mapping file:

<property name="Name" type="string" />
<property name="Value" type="string" />

Name is a regular string/nvarchar(50), and Value is set as ntext in the DB

I'm trying to write a large amount of xml to the "Value" property. I get an exception every time:

@p1 : String truncation: max=4000, len=35287, value='<lots of xml..../>'

I've googled it quite a bit, and tried a number of different mapping configurations:

<property name="Name" type="string" />
<property name="Value" type="string" >
  <column name="Value" sql-type="StringClob" />
</property>

That's one example. Other configurations include "ntext" instead of "StringClob". Those configurations that don't throw mapping exceptions still throw the string truncation exception.

Is this a problem ("feature") with SQL CE? Is it possible to put more than 4000 characters into a SQL CE database with nhibernate? If so, can anyone tell me how?

Many thanks!

Answer 1

Okay, with many thanks to Artur in this thread, here's the solution: Inherit from the SqlServerCeDriver with a new one, and override the InitializeParamter method:

using System.Data;
using System.Data.SqlServerCe;
using NHibernate.Driver;
using NHibernate.SqlTypes;

namespace MySqlServerCeDriverNamespace
{
    /// <summary>
    /// Overridden Nhibernate SQL CE Driver,
    /// so that ntext fields are not truncated at 4000 characters
    /// </summary>
    public class MySqlServerCeDriver : SqlServerCeDriver
    {
        protected override void InitializeParameter(
            IDbDataParameter dbParam,
            string name,
            SqlType sqlType)
        {
            base.InitializeParameter(dbParam, name, sqlType);

            if (sqlType is StringClobSqlType)
            {
                var parameter = (SqlCeParameter)dbParam;
                parameter.SqlDbType = SqlDbType.NText;
            }

        }
    }
}

Then, use this driver instead of NHibernate's in your app.config

<nhibernateDriver>MySqlServerCeDriverNamespace.MySqlServerCeDriver , MySqlServerCeDriverNamespace</nhibernateDriver>

I saw a lot of other posts where people had this problem, and solved it by just changing the sql-type attribute to "StringClob" - as attempted in this thread.

I'm not sure why it wouldn't work for me, but I suspect it is the fact that I'm using SQL CE and not some other DB. But, there you have it!

Answer 2

<property name="Value" type="string" />
  <column name="Value" sql-type="StringClob" />
</property>

I'm assuming this is a small typo, since you've closed the property tag twice. Just pointing this out, in case it wasn't a typo.

Answer 3

Try <property name="Value" type="string" length="4001" />

Answer 4

Tried:

<property name="Value" type="string" length="4001" />

and

<property name="Value" type="string" >
  <column name="Value" sql-type="StringClob" length="5000"/>
</property>

Neither worked, I'm afraid... Same exception - it still says that the max value is 4000.

Answer 5

Why are you using the sub-element syntax?

try:

<property name='Value' type='StringClob' />

Answer 6

On my current deplyoment of SQL CE and NHibernate I use a length of 4001. Then NHibernate generates the stuff as NTEXT instead of NVARCHAR.

Try that.

Another thing to use with NHibernate and SQL CE is:

<session-factory>
  ...
  <property name="connection.release_mode">on_close</property>
</session-factory>

That solves some other problems for me atleast.

Answer 7

After reading your post this modification got it working in my code

protected override void InitializeParameter(IDbDataParameter dbParam,string name,SqlType sqlType)
    {
        base.InitializeParameter(dbParam, name, sqlType);

        var stringType = sqlType as StringSqlType;
        if (stringType != null && stringType.LengthDefined && stringType.Length > 4000)
        {
            var parameter = (SqlCeParameter)dbParam;
            parameter.SqlDbType = SqlDbType.NText;
        }

    }