Core data one-to-one unidirectional relationship

Question

I have 2 entities in which totally 12 properties are there of 3 variations of min, max and average of some particular type of fields. Hence I refactored the 2 entities into 3 entities making the 3rd entity as 'Values' which contains 3 properties ie min, max and average. And reduced the 12 properties into 4 relationships. Here's a replica of my models as an example in the image below.

As you can see I have one-to-one unidirectional relationship with the 3rd entity. However Xcode keeps on complaining about 'Inverse' relationship.

As per me I can add 4 relationships in 'Values' and update all to become 'inverse', however this doesn't seem to be the right solution as when the second entity gets tied to the 'Values', it will have additional 3 nil relationships and whereas in case of first it will have 1 additional nil relationship. Both of these are unnecessary.

Refactoring 'Values' and splitting it into two similar entities also is not a good solution either I believe.

Hence can anyone suggest me what is the right approach or best practice to solve this problem. Let me know if I'm unclear anywhere while describing my issue.

Answer 1

Based on your description, I would undo the refactoring and go back to using properties instead of relationships. You're adding complexity for no real benefit, and the Values entity is (as you're finding) too generic to really be useful or meaningful. This refactoring isn't serving any useful purpose; don't fix it, revert it.

Answer 2

You should look into Weak Relationships (Fetched Properties) for how to manage relationships correctly and the solution for your error code.

Most object relationships are inherently bidirectional. If a Department has a to-many relationship to the Employees who work in a Department, there is an inverse relationship from an Employee to the Department that is to-one. The major exception is a fetched property, which represents a weak one-way relationship—there is no relationship from the destination to the source.

Also, if you want to make things easier, you should look into (if possible) avoid 3 objects and have a single object, or two objects, with the propertiesToFetch of the NSFetchRequest in mind. This way you can fetch your Entity , keep the properties in a single Entity , but only fetch the properties you want and avoid the overhead and memory consumption of fetching properties you are not going to use.

Whichever fits your needs, you have the options. GL