Why is "Fixup" needed for Persistence Ignorant POCO's in EF 4?
- by Eric J.
One of the much-anticipated features of Entity Framework 4 is the ability to use POCO (Plain Old CLR Objects) in a Persistence Ignorant manner (i.e. they don't "know" that they are being persisted with Entity Framework vs. some other mechanism).
I'm trying to wrap my head around why it's necessary to perform association fixups and use FixupCollection in my "plain" business object. That requirement seems to imply that the business object can't be completely ignorant of the persistence mechanism after all (in fact the word "fixup" sounds like something needs to be fixed/altered to work with the chosen persistence mechanism).
Specifically I'm referring to the Association Fixup region that's generated by the ADO.NET POCO Entity Generator, e.g.:
#region Association Fixup
private void FixupImportFile(ImportFile previousValue)
{
if (previousValue != null && previousValue.Participants.Contains(this))
{
previousValue.Participants.Remove(this);
}
if (ImportFile != null)
{
if (!ImportFile.Participants.Contains(this))
{
ImportFile.Participants.Add(this);
}
if (ImportFileId != ImportFile.Id)
{
ImportFileId = ImportFile.Id;
}
}
}
#endregion
as well as the use of FixupCollection. Other common persistence-ignorant ORMs don't have similar restrictions.
Is this due to fundamental design decisions in EF? Is some level of non-ignorance here to stay even in later versions of EF? Is there a clever way to hide this persistence dependency from the POCO developer?
How does this work out in practice, end-to-end? For example, I understand support was only recently added for ObservableCollection (which is needed for Silverlight and WPF). Are there gotchas in other software layers from the design requirements of EF-compatible POCO objects?
