A value that is populated in Codable objects with the DocumentReference of the current document by the Firestore.Decoder when a document is read.

If the field name used for this type conflicts with a read document field, an error is thrown. For example, if a custom object has a field firstName annotated with @DocumentID, and there is a property from the document named firstName as well, an error is thrown when you try to read the document.

When writing a Codable object containing an @DocumentID annotated field, its value is ignored. This allows you to read a document from one path and write it into another without adjusting the value here.

NOTE: Trying to encode/decode this type using encoders/decoders other than Firestore.Encoder leads to an error.

Wraps an Optional field in a Codable object such that when the field has a nil value it will encode to a null value in Firestore. Normally, optional fields are omitted from the encoded document.

This is useful for ensuring a field is present in a Firestore document, even when there is no associated value.

A property wrapper that marks an Optional<Timestamp> field to be populated with a server timestamp. If a Codable object being written contains a nil for an @ServerTimestamp-annotated field, it will be replaced with FieldValue.serverTimestamp() as it is sent.

Example:

struct CustomModel {
  @ServerTimestamp var ts: Timestamp?
}

Then writing CustomModel(ts: nil) will tell server to fill ts with current timestamp.

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 docments 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.