re: Question regarding nullified relationship objects
re: Question regarding nullified relationship objects
- Subject: re: Question regarding nullified relationship objects
- From: Ben Trumbull <email@hidden>
- Date: Mon, 9 Feb 2009 12:14:32 -0800
If I have two entities, A and B, where A <-->>B, and the delete rule
in
entity A's relationship to B is cascade, and B's delete rule for the
relationship to A is nullify, what happens to the actual "row" that
holds
the relationship data in A that was once B after B is deleted? Does
it get
completely deleted, or is it left as garbage that is later cleaned
up, or is
left and later re-filled?
If you delete B first, it nullifies the inverse, and A remains alive
and well. A will then have NULL for its column referring to B's
table. If you delete A first, it cascades the deletion, and
everything will be deleted.
what happens to the actual "row" that holds the relationship data in
A that was once B after B is deleted?
The stuff is deleted. Often it's not a row. There might be a join
table, or there might not. "Implementation dependent" For
educational purposes only, if you want to get a better feel of what's
going on, you can use -com.apple.CoreData.SQLDebug 1 as a user
default. I prefer the command line like:
some.app/Contents/MacOS/some -com.apple.CoreData.SQLDebug 1
Unlike .NET, the association tables are not first class objects of
their own, but rather just a property on the source object.
- Ben
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