Question

I want to validate each entity when saving. That is, I have some custom C# function in each entity class that validates the data.

How can I do that? I don’t want to use database constraints because they cannot express my constraints.

Should I implement some interface???

Answer 1

Entity framework 3.5 and 4.0 offers even called SavingChanges. Entity framework 4.0 and 4.1 has SaveChanges method virtual (as already mentioned).

You can either override method or use event handler and write code like this for 3.5 and 4.0:

var entities = context.ObjectStateManager
                      .GetObjectStateEntries(EntitiState.Modified | EntityState.Added)
                      .Where(e => !e.IsRelationship)
                      .Select(e => e.Entity)
                      .OfType<YourEntityType>();

foreach(var entity in entities)
{
    entity.Validate();
}

In DbContext API (EF 4.1) you must use

var entities = context.ChangeTracker
                      .Entries<YourEntityType>()
                      .Where(e.State == EntityState.Added || e.State == EntityState.Modified)
                      .Select(e => e.Entity);

foreach(var entity in entities)
{
    entity.Validate();
}

You can use custom interface implemented by your entities which will expose Validate method.