SOLVED: Assistance Needed with Predicate Usage in SwiftData Initializer

@kidrong

15d

I encountered some issues while working with predicates within an initializer and bought "SwiftData by Example" hoping to find a solution. Unfortunately, the book did not address my specific problem, so I'm reaching out for guidance.

I'm working with two models in my application: Project and Panel. Here's a brief overview of their structures:

// Project model
import Foundation
import SwiftData

@Model
public class Project {
    var name: String
    @Attribute(.unique) var number: String
    var customer: String
    var details: String
    @Relationship(deleteRule: .cascade) var panels = [Panel]()
    @Attribute(.externalStorage) var photo: Data?
    // Initializer omitted for brevity
}

// Panel model
import Foundation
import SwiftData

@Model
public class Panel {
    @Attribute(.unique) var number: String
    var name: String
    var details: String
    weak var project: Project?
    @Attribute(.externalStorage) var photo: Data?
    // Initializer omitted for brevity
}

The user experience begins with presenting a list of projects. Once a project is selected, the application navigates to a view displaying all panels associated with that project. Here’s the problematic initializer in my Panel view model:

init(searchString: String = "", sortOrder: [SortDescriptor<Panel>] = [], project: Project, path: Binding<NavigationPath>, isEditing: Binding<Bool>) {

        let projectNumber = project.number
        let predicate = #Predicate<Panel> { panel in
            if panel.project?.number == projectNumber {
                if searchString.isEmpty {
                    return true
                } else {
                    return panel.number.localizedStandardContains(searchString)
                    || panel.name.localizedStandardContains(searchString)
                }
            } else {
               return false
            }
        }

        _panels = Query(filter: predicate, sort: sortOrder)
        self.project = project
        _path = path
        _isEditing = isEditing
    }

I'm having trouble when attempting to filter panels by their associated project using a predicate. If I try to add a predicate to check the optional panel.project == project, I encounter an error.

Could you provide any insights or suggestions on what might be going wrong here?

Thank you for your time and help.

@kidrong

14d

Fixed the problem:

Firstly the corect predicate was this all along:

let predicate = #Predicate<Panel> { panel in

            if let panelProjectNumber = panel.project?.number {
                if panelProjectNumber != projectNumber {
                    return false
                } else if searchString.isEmpty {
                    return true
                } else {
                    return panel.number.localizedStandardContains(searchString) ||
                    panel.name.localizedStandardContains(searchString)
                }
            } else {
                return false
            }
        }

        _panels = Query(filter: predicate, sort: sortOrder)

The issue was that while adding a new panel I forgot to also add it to the project.panels array.... This solved it:

func addPanel() {
        isEditing = true
        let newPanel = Panel(number: "", name: "", details: "", project: project)
        project.panels.append(newPanel)
        modelContext.insert(newPanel)
        path.append(newPanel)
    }

I only wasted two days on this... 🤦

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