CoreData: fault: Could not materialize Objective-C class named “Array” from declared attribute value type “Array<String>”

Error

While creating a new iOS App using AI, I encountered above console error on Xcode.

Recently I am working on iCloud backup support using SwiftData.
So I thought it would be related to the task.

But the reason was that words property is String Array.

@Model
final class WordSetModel {
    var name: String
    @Relationship var words: [String]

Problem

We need to add @Relationship attribute to use array for the property in a SwiftData model.

Let’s see words again:

@Relationship var words: [String]

This means WordSet have a relationship with Word, one to many

However String is not Table, so this can’t be work.

Solutions

How to solve?

1. create WordModel

Instead of using String, create a child model

@Model
final class WordModel {
    var text: String
    
    init(text: String, wordSet: WordSetModel? = nil) {
        self.text = text
        self.wordSet = wordSet
    }
}

2. json property

Store array as JSON string.

@Model
final class WordSetModel {
    var name: String
    var words: String
    var wordList: [String] {
      // return parse words..
    }

AI’s solution

WordModel

@Model
final class WordModel {
    var text: String
    @Relationship(inverse: \WordSetModel.words) var wordSet: WordSetModel? // WordSetModel과 관계 설정
    ...
}

WordSetModel

@Model
final class WordSetModel {
    var name: String
    @Relationship(inverse: \WordModel.wordSet) var words: [WordModel]
    ...
}

AI’s solution leads another error

Circular reference resolving attached macro ‘Relationship’

So I asked AI how to solve this and he answered.

WordModel

@Relationship(inverse: \WordSetModel.words, deleteRule: .nullify) var wordSet: WordSetModel? // WordSetModel과 관계 설정

WordSetModel

@Relationship(inverse: \WordModel.wordSet, deleteRule: .cascade) var words: [WordModel]?

However both Parent and child can’t have Relationship inverse parameter All.

I had to fix manually.

I Removed inverse from children, WordModel.

@Relationship var wordSet: WordSetModel? // WordSetModel과 관계 설정

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References

Inferred vs explicit relationships