Question

I have an entity A that used as navigation property for another entity B. I would like to control the Insertion for entity A. Thats meen that whenever I would insert A I have to perform other checks and update other entities.
But when I Insert entities of type B it automatically inserts the connected A entities without the extra checks and updates I need.

How can I solve this?

UPDATE
I decided to use this answer as suggested. But in the OnBeforeInsert() I might add a new entities to the context which their OnBeforeInsert() won’t be called since in the time var changedEntities = ChangeTracker.Entries(); was called the new entitied wasn’t exist yet.
How can I solve this?

Answer 1

EF has very few extension points. So it is sometimes very difficult to customize.

This answer is an extension of my previous answer

public abstract class Entity
{
    public virtual void OnBeforeInsert(){}
    public virtual void OnBeforeUpdate(){}
}

public class Category : Entity
{

    public string Name { get; set; }
    public string UrlName{ get; set; }

    public override void OnBeforeInsert()
    {
       //ur logic
    }
}

Then in your DbContext class subscribe to ObjectStateManagerChanged event of ObjectStateManager.

public class MyContext : DbContext
{
    public override int SaveChanges()
    {
        //intercept entity changes
        UnderlyingObjectContext.ObjectStateManager.ObjectStateManagerChanged 
           += OnObjectStateManagerChanged;

        var changedEntities = ChangeTracker.Entries();

        foreach (var changedEntity in changedEntities)
        {
            if (changedEntity.Entity is Entity)
            {
                var entity = (Entity)changedEntity.Entity;

                switch (changedEntity.State)
                {
                    case EntityState.Added:
                        entity.OnBeforeInsert();
                        break;

                    case EntityState.Modified:
                        entity.OnBeforeUpdate();
                        break;
                }
            }
        }

        return base.SaveChanges();
    }

    ObjectContext UnderlyingObjectContext
    {
         get
         {
              return ((IObjectContextAdapter)this).ObjectContext;
         }
    }

    void OnObjectStateManagerChanged(object sender, CollectionChangeEventArgs e)
    {
        if (e.Action == CollectionChangeAction.Add)
        {
             //not all added entities are new
             if (UnderlyingObjectContext.ObjectStateManager
               .GetObjectStateEntry(e.Element).State == EntityState.Added)
             {
                   if (e.Element is Entity)
                   {
                       ((Entity)e.Element).OnBeforeInsert();
                   }
             }
        }
     }
}

If you are using EF 4.0 you will need to customize this accordingly.