How to query an attribute on an Object contained in a List

I’m using Realm in a Swift project to store my data. I want to use the Realm Swift Query API to query object attributes contained in a List.

My (simplified) objects look like:

open class QuestionModel: Object {
    
    @objc dynamic var uuid: String!
    override public static func primaryKey() -> String? {
        return "uuid"
    }
    // attributes about the media for this question are wrapped up in a MediaModel object
    @objc dynamic var media: MediaModel?
    
}

open class MediaModel: Object {
    // A question can have up to two ImageModels    
    open var images = List<ImageModel>()
   // there are other properties and requirements that justify this Object being here....

}

open class ImageModel: Object {
    // The filename on disk to use to create a UIImage
    @objc dynamic var filename: String? = nil
    // an description of the image
    @objc dynamic var altDescription: String? = nil
   
}

In some circumstances I want to only get QuestionModels where the first ImageModel.filename != “”

Here’s what I’ve tried:

res = realm?.objects(QuestionModel.self)

and I want to further filter the QuestionModels based on certain criteria

Using NSPredicate and Subquery seems to work, though I don’t think it understands which image.name is blank, it just gives me all questions where one of the image.filenames is filled in

res = res.filter("SUBQUERY(media.images, $image, $image.name != '').@count > 0")

However, I really want to move to the new Realm Swift Query API if possible.

res = res.where {
                $0.media.images.name != ""
            }

NSException * “Key paths that include a collection property must use aggregate operations”

res = res.where {
           ($0.media.images.name != "").count > 0
	    }

NSException * “Subqueries must contain a keypath starting with a collection.”

I’m very confused. I can’t seem to find an example online which makes me wonder if this is possible.
Any thought appreciated

Hi Jay,

I was pretty sure I was trying to do the impossible here, and your comments confirmed it. Thanks.

I agree that the first / second image concept is a little odd (there are good reasons for it, I prmise!). However I’ve refactored the requirements a little and my code can now cope with either ImageModel having a blank filename. The order is no longer important.

I just need to get back any QuestionModels that have at least one valid ImageModel.name (i.e. is not blank). I think my NSPredicate SUBQUERY does the right thing here. Would you agree that looks right?

Is there any way to rewrite the SUBQUERY NSPredicate in Swift Query API?

Thanks

Our application (a speech therapy app) allows the user to filter questions on lots of different criteria. These criteria are spread around different objects that all hang off the QuestionModel object. If the users wants the question to be shown on screen as a picture then we also need to restrict the QuestionModels to only those that have images set.

So some psuedo code might be:

res = realm.objects(QuestionModel.self)

if (filter on word length) {
   res = res.where {
      $0.settingsObject.wordLength > 4
  }
}


if (filter on word type) {
   res = res.where {
      $0.settingsObject.wordType == 'Verb'
  }
}


if (display as picture) {
   res = res.filter("SUBQUERY(media.images, $image, $image.name != '').@count > 0")
}

Your idea of creating a relationship back to the QuestionModel looks neat, but it would only work for me if I can use it to further filter down a result set that was originally created from the QuestionModel objects. I don’t know if that’s possible, but if it is I’d be interesting in learning how that works.

Hope that helps to explain a little more of the context for this question, and I really appreciate you taking the time to respond.

Brilliant. I’m going to go the NSPredicate and SUBQUERY route as a solution.
Thanks for helping me work through this