YsA.Net

Today I'm hosting a post from Leeran Yarhi, one of the developers in my team:

Hi guys,

I’m Leeran Yarhi, a developer in Yossi’s team.

Recently we had a problem while mapping one of our domain entities with Fluent NHibernate. We upgraded our app to use NHibernate 3 in conjunction with Fluent NHibernate 1.2. When we did that, some of our tests failed.

For example, let’s have a look at this entity:

public class User

{

    public virtual int Id { get; set; }

    public virtual string FirstName { get; set; }

    public virtual string LastName { get; set; }

    public virtual string FullName { get; private set; }

}

And it’s mapping:

public class UserMap : ClassMap<User>

{

   public UserMap()

   {

       Id(x => x.Id);

       Map(x => x.FirstName);

       Map(x => x.LastName);

       Map(x => x.FullName).Formula("first_name || ' ' || last_name");

   }

}

As you can see, User has a property named FullName, which is actually a concatenation of FirstName and LastName. Of course I don’t really want to map this property to our Database. This is why I’m defining it a Formula, so that my Users table won’t really have a column for FullName

All good, but the problem starts when I try to use this PropertyConvention :

public class PropertyUnderscoreConvention : IPropertyConvention

{

    public void Apply(IPropertyInstance instance)

    {

        instance.Column(Inflector.Underscore(instance.Property.Name));

    }

}

NHibernate will throw an exception because it’s trying to give a name to a column that doesn’t exist. The solution for this problem is to somehow define to my convention when it should apply, or in other words – Acceptance Criteria.

Fluent NHibernate gives us an API for defining the criteria that a mapping must satisfy for a convention to be applied to it. Exactly what I need.

The Convention class will now implement another interface: IAcceptanceCriteria<TInspector> , which contains the method Accept. This method defines the above criteria.

Let’s see some code, this is how my new convention looks like:

public interface IPropertyConventionAcceptance : IConventionAcceptance<IPropertyInspector>    

{

}     

public class PropertyConvention : IPropertyConvention, IPropertyConventionAcceptance

{

    public void Apply(IPropertyInstance instance)

    {

        instance.Column(Inflector.Underscore(instance.Property.Name));

    }

    public void Accept(IAcceptanceCriteria<IPropertyInspector> criteria)

    {

        criteria.Expect(x => x.Formula == null);

    }

}