Tip 33 – How cascade delete really works in EF

re: Tip 33 – How cascade delete really works in EF

kiran — Tue, 14 Aug 2012 09:08:28 GMT

Hi Alex,

I couldn't get you , how exactly you override SaveChanges and delete all the Dependents.Can you explain with little more detail.It would be helpful if provided a sample code or with an example.

re: Tip 33 – How cascade delete really works in EF

Alex D James — Sat, 12 Dec 2009 23:53:28 GMT

Thomas,

Well you could do this by overriding SaveChanges, enumerating all the objectStateEntries in the ObjectContext.ObjectStateManager, looking for those in the deleted state.

When you find one of the right type, you could have a rule that loads all the dependents, then when you finally call through to base.SaveChanges() EF would delete *all* the dependents even if there isn't a cascade delete rule in the database.

Alex

re: Tip 33 – How cascade delete really works in EF

Thomas — Sat, 12 Dec 2009 21:27:27 GMT

Hi,

I am used to a different ORM based on ActiveRecord where it is possible to ensure that additional cleanup is performed on delete if necessary.

This obviously comes at a cost as you need to retrieve the related entity in order to carry out its ondelete cleanup.

Lets say we have a Blog with Post that can have Attachments, and the actual files are stored on a file server with only a path in the database.

Now I want to ensure that deleting a Blog or a Post will always cleanup the files in the file system too.

How would you go about implementing that in EF?

Thanks,

Thomas

re: Tip 33 – How cascade delete really works in EF

Alex D James — Sat, 28 Nov 2009 06:18:01 GMT

@Luke,

Absolutely, you should have the a cascade delete rule in the database, because EF can't be relied upon to delete every entity. It will only delete entities it knows about (i.e. that are in memory).

Alex

re: Tip 33 – How cascade delete really works in EF

Luke — Sat, 28 Nov 2009 03:42:29 GMT

So just for clarification, since #2 is not recommended, are you saying that the #1 recommended approach is having a cascading delete set up on the physical database? Thanks.

re: Tip 33 – How cascade delete really works in EF

CodeWarrior — Wed, 18 Nov 2009 23:05:21 GMT

Hi,

I have a question. When I tried adding the OnDelete action I still get the following error.

{"The DELETE statement conflicted with the REFERENCE constraint \"FK_Orders_Customers\". The conflict occurred in database \"C:\\METADATAPROVIDERSAMPLE\\METADATAPROVIDERWEBSITE\\APP_DATA\\NORTHWND.MDF\", table \"dbo.Orders\", column 'CustomerID'.\r\nThe statement has been terminated."}

Here is my code:

NORTHWNDEntities1 ne = new NORTHWNDEntities1();

var originalEntity = (from entity in ne.Customers

where entity.CustomerID == "ANTON" select entity).FirstOrDefault();

ne.DeleteObject(originalEntity);

ne.SaveChanges(true);

Here is the XML file contents:

</End>

</End>

</Principal>

</Dependent>

</ReferentialConstraint>

</Association>

Oh, and I did make the changes in the database.

Any help would be greatly appreciated!!!

Thanks

CodeWarrior