In Xcode you can setup constraints for a Core Data entity with the Data Model Inspector in the Constraints area. For every constraint added via + it set the example constraint "comma,separated,properties". You can configure more than one such constraint.
In the model file it looks like this:
<entity>
…
<uniquenessConstraints>
<uniquenessConstraint>
<constraint value="parent"/>
<constraint value="title"/>
<constraint value="birthday"/>
</uniquenessConstraint>
<uniquenessConstraint>
<constraint value="firstName"/>
<constraint value="lastName"/>
</uniquenessConstraint>
</uniquenessConstraints>
</entity>
Question: What it the logic? How to read this? Is it AND or OR inside a constraint? Is it AND or OR between multiple constraints?
While testing i came to this conclusion:
- Every constraint says: All attributes in this constraint must have the same value for two ManagedObjects to match
- Only one constraint is required to match in order for two ManagedObjects to match
This means:
- The attributes (constraint values) must all match per constraint (AND)
- At least one constraint must match (OR)
Or with an example: Two ManagedObjects would match, if they have (the same parent AND title AND birthday) OR (the same firstName AND lastName).
Is this correct?
In this developer video https://developer.apple.com/videos/play/wwdc2015/220/?time=821
they're importing recipe data from various sources and configure one constraint to avoid duplicates: "source,externlID". This looks like source and externlID must match both (AND) to identify a duplicate. This would support my interpretation for constraints above.
