SOLVED: Dynamically filtering @FetchRequest with SwiftUI + Distinct Values

@fpozatto

Mar '22

Hello,

I succesfully implemented the code under the topic "Dynamically filtering @FetchRequest with SwiftUI", and works greatly.

https://www.hackingwithswift.com/books/ios-swiftui/dynamically-filtering-fetchrequest-with-swiftui

However, I need to return only the Distinct values in the List. I do understand I should add these properties:

fetchRequest.resultType = NSDictionaryResultType;
fetchRequest.propertiesToFetch = [NSArray arrayWithObject:[[entity propertiesByName] objectForKey:@"name"]];
fetchRequest.returnsDistinctResults = YES;

But I can't seem to find th syntax on doing that in this _fetchRequest scenario.

It seema purely a syntax question, and any help is appreciated.

Thank you!

@Hatsushira HWS+

Mar '22

From my understanding these are properties of NSFetchRequest from CoreData not FetchRequest from SwiftUI. So you can't set these properties because they don't exist.

@roosterboy HWS+

Mar '22

Instead of doing this:

init(filter: String) {
    _fetchRequest = FetchRequest<Singer>(sortDescriptors: [], predicate: NSPredicate(format: "lastName BEGINSWITH %@", filter))
}

You would need to use a different initializer on FetchRequest and pass in a configured NSFetchRequest that has its properties set as you need. Something like this:

//first, an extension on your managed object class
extension Singer {
    static var distinctSingers: NSFetchRequest<Singer> = {
        let request = NSFetchRequest<Singer> = Singer.fetchRequest()
        //set up the properties you need
        request.resultType = .dictionaryResultType
        request.propertiesToFetch = ["name"]
        request.returnsDistinctResults = true
        return request
    }
}

//then, in your View's init:

init(filter: String) {
    let request = Singer.distinctSingers
    //add any other specialization to the request, like sort descriptors or predicates
    request.predicate = NSPredicate(format: "lastName BEGINSWITH %@", filter)
    //and then initialize the property wrapper with the request
    _fetchRequest = FetchRequest<Singer>(fetchRequest: request)
}

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