实体框架中的合并

Question

Is there a way to call T-Sql's MERGE command from .NET Entity framework 4?

Answer 1

No there no such built-in functionality - you must build your own. Very common is for example approach like:

public void SaveOrUpdate(MyEntity entity)
{
    if (entity.Id == 0)
    {
        context.MyEntities.AddObject(entity);
    }
    else
    {
        context.MyEntities.Attach(entity);
        context.ObjectStateManager.ChangeObjectState(entity, EntityState.Modified);
    }

    // You can call SaveChanges here or you can call it separately after multiple changes
}

This is example for working with detached entity which have Id auto generated in the database ( IDENTITY ). Default Id for new entity is always 0 because the real value will be assigned during saving changes.