11

I'm trying to fetch some results with the new #Predicate macro. The problem appears when I try to use an enum property inside the predicate. Does anyone know if it can be done or if this is a bug?

XCode 15 beta 4

Fetch 1:

let predicate = #Predicate<ModelA> { $0.type == ModelA.ModelAType.a }

Fetch 2:

let predicate = #Predicate<ModelA> { $0.type.rawValue == ModelA.ModelAType.a.rawValue }

Model:

@Model final class ModelA: Codable {
    @Attribute(.unique) var id: Int64 = 0
    enum ModelAType: Int, CaseIterable, Codable { case a = 1, b }
    var type: ModelAType = ModelAType.a
}

Errors:

Type 'ModelA.Type' cannot conform to 'StandardPredicateExpression'
Type 'ModelA.Type' cannot conform to 'PredicateExpression'
Cannot infer key path type from context; consider explicitly specifying a root type

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2 Answers 2

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5

As of Xcode 15.2 this doesn't seem to work at all if you want to use an enum in a predicate, a workaround is to store the raw value of the enum directly and use a computed property to convert between the stored value and the enum type.

What worked for me in this situation was to define a constant for the raw value and use that constant in the predicate

let aValue = ModelA.ModelAType.a.rawValue
let predicate = #Predicate<ModelA> { $0.type.rawValue == aValue }

I am not sure why this is needed but hopefully it’s a beta thing that will change soon

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6 Comments

doesn't seem to work on XCode 15.1 beta 3 and simulator 17.2
@AndroidGecko Seems we have a regression, I can't make it work either even though I tried several different variants.
Also doesnt work for me with Xcode 15.2 and Simulator 17.2
For me storing the actual enum case in a constant and then using worked fine (without the .rawValue)
This seems to get be past the compile error however when fetching it seems to lead to a different one SwiftData/DataUtilities.swift:65: Fatal error: Couldn't find \enum.rawValue
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3

I found a workaround.

  1. Create a property type of Int for represent the rawValue enum.
  2. Create a getter/setter property to represent/resolver your enum.
  3. In your #Predicate, use Int property to compare.

Follow the solution:

enum PlanStatus: Int, Codable {
    case working, standby, inactive
}

@Model
final class Plan: Identifiable, Hashable {
    
    // MARK: - Public Properties
    
    @Attribute(.unique)
    private(set) var id: UUID
    
    private(set) var createdAt: Date
    
    var title: String
    var start: Date
    var end: Date
    
    var status: PlanStatus {
        get { PlanStatus(rawValue: _status)! }
        set { _status = newValue.rawValue }
    }
    
    // MARK: - Private Properties
    
    private var _status: PlanStatus.RawValue
    
    // MARK: - Life Cycle
    
    init(
        _ title: String,
        start: Date,
        end: Date,
        status: PlanStatus = .standby
    ) {
        id = UUID()
        createdAt = .now
        
        self.title = title
        self.start = start
        self.end = end
        
        _status = status.rawValue
    }
    
}

In your predicate use:

let sortBy = [SortDescriptor<Plan>(\.createdAt, order: .reverse)]
let state = PlanStatus.inactive
let predicate = #Predicate<Plan> { $0._status == status.rawValue }
let descriptor = Plan.fetchDescriptor(predicate: predicate, sortBy: sortBy)
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1 Comment

you made _status private and then you use it in the descriptor. this might be a typo since that code couldn't build. other than that, the solution as a whole works.

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