FirestoreQuery

@available(iOS 14.0, macOS 11.0, tvOS 14.0, watchOS 7.0, *)
@propertyWrapper
public struct FirestoreQuery<T> : DynamicProperty

A property wrapper that listens to a Firestore collection.

In the following example, FirestoreQuery will fetch all documents from the fruits collection, filtering only documents whose isFavourite attribute is equal to true, map members of result set to the Fruit type, and make them available via the wrapped value fruits.

struct ContentView: View {
  @FirestoreQuery(
    collectionPath: "fruits",
    predicates: [.whereField("isFavourite", isEqualTo: true)]
  ) var fruits: [Fruit]

  var body: some View {
    List(fruits) { fruit in
      Text(fruit.name)
    }
  }
}

FirestoreQuery also supports returning a Result type. The .success case returns an array of elements, whereas the .failure case returns an error in case mapping the Firestore documents wasn’t successful:

struct ContentView: View {
  @FirestoreQuery(
    collectionPath: "fruits",
    predicates: [.whereField("isFavourite", isEqualTo: true)]
  ) var fruitResults: Result<[Fruit], Error>

var body: some View {
  if case let .success(fruits) = fruitResults {
    List(fruits) { fruit in
      Text(fruit.name)
    }
  } else if case let .failure(error) = fruitResults {
    Text("Couldn't map data: \(error.localizedDescription)")
  }
}

Alternatively, the projected value of the property wrapper provides access to the error as well. This allows you to display a list of all successfully mapped documents, as well as an error message with details about the documents that couldn’t be mapped successfully (e.g. because of a field name mismatch).

struct ContentView: View {
  @FirestoreQuery(
    collectionPath: "mappingFailure",
    decodingFailureStrategy: .ignore
  ) private var fruits: [Fruit]

  var body: some View {
    VStack(alignment: .leading) {
      List(fruits) { fruit in
        Text(fruit.name)
      }
      if $fruits.error != nil {
        HStack {
          Text("There was an error")
            .foregroundColor(Color(UIColor.systemBackground))
          Spacer()
        }
        .padding(30)
        .background(Color.red)
      }
    }
  }
}

Internally, @FirestoreQuery sets up a snapshot listener and publishes any incoming changes via an @StateObject.

The projected value of this property wrapper provides access to a configuration object of type FirestoreQueryConfiguration which can be used to modify the query criteria. Changing the filter predicates results in the underlying snapshot listener being unregistered and a new one registered.

Button("Show only Apples and Oranges") {
  $fruits.predicates = [.whereField("name", isIn: ["Apple", "Orange]]
}

This property wrapper does not support updating the wrappedValue, i.e. you need to use Firestore’s other APIs to add, delete, or modify documents.