Änderungen an Abfrageergebnissen mit Firestore Watch überwachen
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Änderungen an Abfrageergebnissen mit Firestore Watch überwachen
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[[["Leicht verständlich","easyToUnderstand","thumb-up"],["Mein Problem wurde gelöst","solvedMyProblem","thumb-up"],["Sonstiges","otherUp","thumb-up"]],[["Schwer verständlich","hardToUnderstand","thumb-down"],["Informationen oder Beispielcode falsch","incorrectInformationOrSampleCode","thumb-down"],["Benötigte Informationen/Beispiele nicht gefunden","missingTheInformationSamplesINeed","thumb-down"],["Problem mit der Übersetzung","translationIssue","thumb-down"],["Sonstiges","otherDown","thumb-down"]],[],[[["\u003cp\u003eThis document demonstrates how to monitor changes in query results using Firestore Watch across multiple languages including C#, Go, Java, Node.js, Python, and Ruby.\u003c/p\u003e\n"],["\u003cp\u003eThe code examples provided show how to set up a listener that triggers a callback function whenever there are changes to a Firestore query, specifically when filtering for cities in California ("CA").\u003c/p\u003e\n"],["\u003cp\u003eTo use Firestore effectively, it requires authentication setup using Application Default Credentials, as detailed in the provided documentation link.\u003c/p\u003e\n"],["\u003cp\u003eThe sample code for each language utilizes a similar approach, involving the creation of a query, setting up an event listener, and defining a callback function to process the snapshot of the query results.\u003c/p\u003e\n"]]],[],null,["# Monitor query result changes with Firestore Watch\n\nExplore further\n---------------\n\n\nFor detailed documentation that includes this code sample, see the following:\n\n- [Get real-time updates](/firestore/native/docs/query-data/listen)\n- [Get realtime updates with Cloud Firestore](https://firebase.google.com/docs/firestore/query-data/listen)\n\nCode sample\n-----------\n\n### C#\n\n\nTo authenticate to Firestore, set up Application Default Credentials.\nFor more information, see\n\n[Set up authentication for a local development environment](/docs/authentication/set-up-adc-local-dev-environment).\n\n CollectionReference citiesRef = db.Collection(\"cities\");\n Query query = db.Collection(\"cities\").WhereEqualTo(\"State\", \"CA\");\n\n FirestoreChangeListener listener = query.Listen(snapshot =\u003e\n {\n Console.WriteLine(\"Callback received query snapshot.\");\n Console.WriteLine(\"Current cities in California:\");\n foreach (DocumentSnapshot documentSnapshot in snapshot.Documents)\n {\n Console.WriteLine(documentSnapshot.Id);\n }\n });\n\n### Go\n\n\nTo authenticate to Firestore, set up Application Default Credentials.\nFor more information, see\n\n[Set up authentication for a local development environment](/docs/authentication/set-up-adc-local-dev-environment).\n\n import (\n \t\"context\"\n \t\"fmt\"\n \t\"io\"\n \t\"time\"\n\n \t\"cloud.google.com/go/firestore\"\n \t\"google.golang.org/api/iterator\"\n \t\"google.golang.org/grpc/codes\"\n \t\"google.golang.org/grpc/status\"\n )\n\n // listenMultiple listens to a query, returning the names of all cities\n // for a state.\n func listenMultiple(ctx context.Context, w io.Writer, projectID, collection string) error {\n \t// projectID := \"project-id\"\n \tctx, cancel := context.WithTimeout(ctx, 30*time.Second)\n \tdefer cancel()\n\n \tclient, err := firestore.NewClient(ctx, projectID)\n \tif err != nil {\n \t\treturn fmt.Errorf(\"firestore.NewClient: %w\", err)\n \t}\n \tdefer client.Close()\n\n \tit := client.Collection(collection).https://cloud.google.com/go/docs/reference/cloud.google.com/go/firestore/latest/index.html#cloud_google_com_go_firestore_Query_Where(\"state\", \"==\", \"CA\").Snapshots(ctx)\n \tfor {\n \t\tsnap, err := it.Next()\n \t\t// DeadlineExceeded will be returned when ctx is cancelled.\n \t\tif status.Code(err) == codes.DeadlineExceeded {\n \t\t\treturn nil\n \t\t}\n \t\tif err != nil {\n \t\t\treturn fmt.Errorf(\"Snapshots.Next: %w\", err)\n \t\t}\n \t\tif snap != nil {\n \t\t\tfor {\n \t\t\t\tdoc, err := snap.Documents.Next()\n \t\t\t\tif err == iterator.Done {\n \t\t\t\t\tbreak\n \t\t\t\t}\n \t\t\t\tif err != nil {\n \t\t\t\t\treturn fmt.Errorf(\"Documents.Next: %w\", err)\n \t\t\t\t}\n \t\t\t\tfmt.Fprintf(w, \"Current cities in California: %v\\n\", doc.Ref.ID)\n \t\t\t}\n \t\t}\n \t}\n }\n\n### Java\n\n\nTo authenticate to Firestore, set up Application Default Credentials.\nFor more information, see\n\n[Set up authentication for a local development environment](/docs/authentication/set-up-adc-local-dev-environment).\n\n db.collection(\"cities\")\n .whereEqualTo(\"state\", \"CA\")\n .addSnapshotListener(\n new EventListener\u003cQuerySnapshot\u003e() {\n @Override\n public void onEvent(\n @Nullable QuerySnapshot snapshots, @Nullable FirestoreException e) {\n if (e != null) {\n System.err.println(\"Listen failed:\" + e);\n return;\n }\n\n List\u003cString\u003e cities = new ArrayList\u003c\u003e();\n for (DocumentSnapshot doc : snapshots) {\n if (doc.get(\"name\") != null) {\n cities.add(doc.getString(\"name\"));\n }\n }\n System.out.println(\"Current cites in CA: \" + cities);\n }\n });\n\n### Node.js\n\n\nTo authenticate to Firestore, set up Application Default Credentials.\nFor more information, see\n\n[Set up authentication for a local development environment](/docs/authentication/set-up-adc-local-dev-environment).\n\n const query = db.collection('cities').where('state', '==', 'CA');\n\n const observer = query.onSnapshot(querySnapshot =\u003e {\n console.log(`Received query snapshot of size ${querySnapshot.size}`);\n // ...\n }, err =\u003e {\n console.log(`Encountered error: ${err}`);\n });\n\n### Python\n\n\nTo authenticate to Firestore, set up Application Default Credentials.\nFor more information, see\n\n[Set up authentication for a local development environment](/docs/authentication/set-up-adc-local-dev-environment).\n\n\n # Create an Event for notifying main thread.\n callback_done = threading.Event()\n\n # Create a callback on_snapshot function to capture changes\n def on_snapshot(col_snapshot, changes, read_time):\n print(\"Callback received query snapshot.\")\n print(\"Current cities in California:\")\n for doc in col_snapshot:\n print(f\"{doc.id}\")\n callback_done.set()\n\n col_query = db.collection(\"cities\").where(filter=FieldFilter(\"state\", \"==\", \"CA\"))\n\n # Watch the collection query\n query_watch = col_query.on_snapshot(on_snapshot)\n\n### Ruby\n\n\nTo authenticate to Firestore, set up Application Default Credentials.\nFor more information, see\n\n[Set up authentication for a local development environment](/docs/authentication/set-up-adc-local-dev-environment).\n\n query = firestore.col(collection_path).where :state, :==, \"CA\"\n docs = []\n\n # Watch the collection query.\n listener = query.listen do |snapshot|\n puts \"Callback received query snapshot.\"\n puts \"Current cities in California:\"\n snapshot.docs.each do |doc|\n puts doc.document_id\n docs \u003c\u003c doc\n end\n end\n\nWhat's next\n-----------\n\n\nTo search and filter code samples for other Google Cloud products, see the\n[Google Cloud sample browser](/docs/samples?product=firestore)."]]