Question

I got an error from core-data that a value “” could not be parsed.
This value belonged to a non optional entity attribute of type double with 0 as default.

What can cause such data corruption?

Answer 1

I think the answer to your question “what could cause such data corruption” is “faulting”.

Core data will only fetch the attributes when it needs them. This is a feature, not a bug, as it helps manage memory and performance efficiently behind the scenes. However, if you use a construct returned by a core data fetch (such as an array with fetch results) and construct an XLM it is conceivable that the faults are not filled (i.e., Core Data does not go to the persistent store to fetch the faulted data automatically).

Your observation that everything is there once you explicitly call the relationship like in children = entity.children corroborates this thesis.

So -no, not access observers, but faulting is responsible for your data loss.