let storage = CoreDataStorage(container: NSPersistentContainer(name: "Model"))

storage.mainContext // Automatically merges changes from parent context
storage.privateContext // Created once as new background context

let cancellable = storage
    .performInBackgroundAndSave { context in
        // work with background context
    }
    .receive(on: DispatchQueue.main)
    .sink(
        receiveCompletion: { completion in
        // process completion on main queue
    },
        receiveValue: { value in
        //
    })

let cancellable = storage
    .fetch(Item.fetchItems(), inContext: .background)
    .receive(on: DispatchQueue.main)
    .sink(
        receiveCompletion: { completion in
        // process completion on main queue
    },
        receiveValue: { value in
            let items: [Item] = value
    })

private static let managedObjectModel = CoreDataModel {
    Entity(name: "Item", className: Item.self) {
        Property(name: "id", type: .UUIDAttributeType)
        Property(name: "name", type: .stringAttributeType, isOptional: true)
    }
}.build()

private final class Item: NSManagedObject {
    @NSManaged var id: UUID
    @NSManaged var name: String?
}

let container = NSPersistentContainer(name: "Temp", managedObjectModel: managedObjectModel)
let description = NSPersistentStoreDescription()
description.type = NSInMemoryStoreType
description.shouldAddStoreAsynchronously = false
container.persistentStoreDescriptions = [description]