Fluent NHibernate and computed properties

Question

I\'m using Fluent NHibernate, and auto-mapping the classes.

I have a computed property in a class along the lines of

public virtual DateTime? LastAct         


        

Answer 1

I'm not certain you can do that with NHibernate, but I could be wrong. NHibernate translates your criteria into SQL, and thus that property wouldn't be available to query with (it ain't in the db!).

However, if I'm wrong (and that's frequent), you should be able to map it with an override.

In your automapping setup, create an override and map that property explicitly using the Access property to tell NHibernate how to treat it.

Something like this:

AutoMap.AssemblyOf<YourEntity>()
  // automapping stuff
  .Override<ThatClass>(m =>
  {
    m.Map(x => x.LastActionTimeStamp)
      .Access.None();
  });

Answer 2

You can also override the mapping and ignore the propery:

public class ThatClassMappingOverride : IAutoMappingOverride<ThatClass>
{
  public void Override(AutoMapping<ThatClass> mapping)
        {
            mapping.IgnoreProperty(x=> x.PropertyToIgnore);
        }
}

Answer 3

You could associate a formula with the property and use that instead of the c# code. e.g.

Property:

private int _postCount = 0;
public virtual int PostCount
{
    get
    {
        return _postCount;
    }
}

Formula:

(SELECT count(p.ID) FROM BlogPost p WHERE p.BlogID = ID and p.IsDeleted = 0)

And then you can use PostCount in your expression as usual. Remember to set the access modifier on the property in your FluentMapping. Not sure what Fluent supports but the options I have found for normal mapping are:

* property
* field
* field.camelcase
* field.camelcase-underscore
* field.pascalcase-m-underscore
* field.lowercase-underscore
* nosetter.camelcase
* nosetter.camelcase-underscore
* nosetter.pascalcase-m-underscore
* nosetter.lowercase-underscore

Probably best check out NHibernate documentation for the official list Access Strategies so you combine the access strategy with the naming strategy e.g. "field.lowercase-underscore"