core-data

Core Data

iOS persistence with Core Data and SwiftData.

Core Data Stack

Basic Setup

// ✅ Core Data stack
class PersistenceController {
    static let shared = PersistenceController()

    let container: NSPersistentContainer

    init(inMemory: Bool = false) {
        container = NSPersistentContainer(name: "DataModel")

        if inMemory {
            container.persistentStoreDescriptions.first?.url = URL(fileURLWithPath: "/dev/null")
        }

        container.loadPersistentStores { description, error in
            if let error = error {
                fatalError("Core Data store failed to load: \(error)")
            }
        }

        container.viewContext.automaticallyMergesChangesFromParent = true
        container.viewContext.mergePolicy = NSMergeByPropertyObjectTrumpMergePolicy
    }

    var viewContext: NSManagedObjectContext {
        container.viewContext
    }

    func backgroundContext() -> NSManagedObjectContext {
        container.newBackgroundContext()
    }
}

SwiftUI Integration

// ✅ @FetchRequest in SwiftUI
struct UserListView: View {
    @Environment(\.managedObjectContext) private var viewContext

    @FetchRequest(
        sortDescriptors: [NSSortDescriptor(keyPath: \User.name, ascending: true)],
        animation: .default)
    private var users: FetchedResults<User>

    var body: some View {
        List {
            ForEach(users) { user in
                Text(user.name ?? "Unknown")
            }
            .onDelete(perform: deleteUsers)
        }
    }

    private func deleteUsers(offsets: IndexSet) {
        withAnimation {
            offsets.map { users[$0] }.forEach(viewContext.delete)

            do {
                try viewContext.save()
            } catch {
                print("Failed to save: \(error)")
            }
        }
    }
}

Fetch Requests

Basic Fetch

// ✅ Simple fetch
func fetchUsers() -> [User] {
    let request: NSFetchRequest<User> = User.fetchRequest()
    request.sortDescriptors = [NSSortDescriptor(key: "name", ascending: true)]

    do {
        return try viewContext.fetch(request)
    } catch {
        print("Fetch error: \(error)")
        return []
    }
}

// ✅ With predicate
func fetchUsers(named name: String) -> [User] {
    let request: NSFetchRequest<User> = User.fetchRequest()
    request.predicate = NSPredicate(format: "name == %@", name)
    request.fetchLimit = 1

    do {
        return try viewContext.fetch(request)
    } catch {
        return []
    }
}

// ✅ Complex predicate
func searchUsers(query: String) -> [User] {
    let request: NSFetchRequest<User> = User.fetchRequest()
    request.predicate = NSPredicate(
        format: "name CONTAINS[cd] %@ OR email CONTAINS[cd] %@",
        query, query
    )
    request.sortDescriptors = [NSSortDescriptor(key: "name", ascending: true)]

    do {
        return try viewContext.fetch(request)
    } catch {
        return []
    }
}