struct TodoItem: Document, Codable {
  static let documentDescriptor = DocumentDescriptor<TodoItem>(name: "TodoItem",
                                                               identifier: Identifier(keyPath: \.id),
                                                               indices: [
                                                                 Index(name: "completed", keyPath: \.completed)
                                                               ])

  let id: Int
  let text: String
  let completed: Bool
}

let documentStore = try DocumentStore(identifier: "TodoStore",
                                      documentDescriptors: [TodoItem.documentDescriptor])

let todoItem = TodoItem(id: 1, text: "Give DocumentStore a try", completed: false)

documentStore.write(handler: { result in
  if case let .failure(error) = result {
    fatalError(error)
  }
}, actions: { transaction in
  try transaction.insert(document: todoItem)
  return .saveChanges
})

let uncompletedQuery = Query<TodoItem>()
  .sorted(by: \.id, order: .ascending)
  .filtered { _ in !\.completed }

documentStore.read(handler: { result in
  switch result {
  case let .success(todoItems):
    debugPrint(todoItems)
  case let .failure(error):
    fatalError(error)
  }
}, actions: { transaction in
  try transaction.fetch(matching: uncompletedQuery)
})