Temporarily turn off identity column with Fluent AutoMap? - nhibernate

Question

I have begun to test Fluent NHibernate in C#
I have a well normalized object structure with 20 related classes.
I currently use Fluent 1.3 with NHibernate 3.2.
So far I have managed to use the AutoMap feature which suits me fine,
Very convenient!
BUT ...
3 of the tables are "enum tables" that need to have their records set with specific Id value.
I tried to make manual mappings of these tables and let the rest be automapped.
But when the manual table is created it fails because it references a table that is automapped (and not available for manual mapper?)
Is it possible to use AutoMapping but for some very few classes override identity creation on primary key?
I tried to make a custom convention but without success.
public class OverrideIdentityGeneration : Attribute
{
}
public class ConventionIdentity : AttributePropertyConvention<OverrideIdentityGeneration>
{
protected override void Apply(OverrideIdentityGeneration attribute, IPropertyInstance instance)
{
instance.Generated.Never();
}
}
Is there some other way?
It would be sad to be forced back to use manual mapping for all classes ....

Answer 1

class MyIdConvention : IIdConvention
{
public void Apply(IIdentityInstance instance)
{
if (instance.EntityType == ...)
{
instance.GeneratedBy.Assigned();
}
}
}
Update:
for enum-like classes it's often easier to define an enum as id
class ConfigValue
{
public virtual Config Id { get; set; }
}
// the convention is easy
if (instance.EntityType.IsEnum)
{
instance.GeneratedBy.Assigned();
// to save as int and not string
instance.CustomType(typeof(Config));
}
// querying without magic int values
var configValue = Session.Get<ConfigValue>(Config.UIColor);

Answer 2

I used the idea given by Fifo and extended it to use a custom attribute instead.
To make code readable and avoid redundance when using similar idea in other conventions I added an extension method to check for custom attribute.
This is the code I ended up with:
/// <summary>
/// Convention to instruct FluentNHIbernate to NOT generate identity columns
/// when custom attribute is set.
/// </summary>
public class ConventionIdentity : IIdConvention
{
public void Apply(IIdentityInstance instance)
{
if(instance.CustomAttributeIsSet<NoIdentity>())
instance.GeneratedBy.Assigned();
}
}
/// <summary>
/// Custom attribute definition.
/// </summary>
public class NoIdentity : Attribute
{
}
/// <summary>
/// Example on how to set attribute.
/// </summary>
public class Category
{
[NoIdentity]
public int Id { get; set; }
public string Name { get; set; }
}
public static class IInspectorExtender
{
/// <summary>
/// Extender to make convention usage easier.
/// </summary>
public static T GetCustomAttribute<T>(this IInspector instance)
{
var memberInfos = instance.EntityType.GetMember(instance.StringIdentifierForModel);
if(memberInfos.Length > 0)
{
var customAttributes = memberInfos[0].GetCustomAttributes(false);
return customAttributes.OfType<T>().FirstOrDefault();
}
return default(T);
}
}