離線存取資料

Cloud Firestore 支援離線資料保存功能。這項功能會快取應用程式目前使用的 Cloud Firestore 資料副本，讓您的應用程式可在裝置離線時存取資料。您可以寫入、讀取、聆聽及查詢快取資料。裝置恢復連線後，Cloud Firestore 會將應用程式所做的任何本機變更同步到 Cloud Firestore 後端。

如要使用離線持久性，您不必對用來存取 Cloud Firestore 資料的程式碼進行任何變更。啟用離線持續性功能後，Cloud Firestore 用戶端程式庫會自動管理線上和離線資料存取作業，並在裝置恢復連線時同步處理本機資料。

設定離線持續性

初始化 Cloud Firestore 時，您可以啟用或停用離線持續性：

  • Android 和 Apple 平台預設啟用離線保存功能。如要停用持久性，請將 PersistenceEnabled 選項設為 false。
  • 在網頁版中，離線持久性預設為停用。如要啟用持久性，請呼叫 enablePersistence 方法。系統不會自動清除工作階段之間的 Cloud Firestore 快取。因此，如果您的網頁應用程式會處理敏感資訊，請務必先詢問使用者是否使用可信任的裝置，再啟用持續性功能。

Web

// Memory cache is the default if no config is specified.
initializeFirestore(app);

// This is the default behavior if no persistence is specified.
initializeFirestore(app, {localCache: memoryLocalCache()});

// Defaults to single-tab persistence if no tab manager is specified.
initializeFirestore(app, {localCache: persistentLocalCache(/*settings*/{})});

// Same as `initializeFirestore(app, {localCache: persistentLocalCache(/*settings*/{})})`,
// but more explicit about tab management.
initializeFirestore(app, 
  {localCache: 
    persistentLocalCache(/*settings*/{tabManager: persistentSingleTabManager()})
});

// Use multi-tab IndexedDb persistence.
initializeFirestore(app, 
  {localCache: 
    persistentLocalCache(/*settings*/{tabManager: persistentMultipleTabManager()})
  });

Web

firebase.firestore().enablePersistence()
  .catch((err) => {
      if (err.code == 'failed-precondition') {
          // Multiple tabs open, persistence can only be enabled
          // in one tab at a a time.
          // ...
      } else if (err.code == 'unimplemented') {
          // The current browser does not support all of the
          // features required to enable persistence
          // ...
      }
  });
// Subsequent queries will use persistence, if it was enabled successfully
test.firestore.js
Swift
注意：這項產品不適用於 watchOS 和 App Clip 目標。
let settings = FirestoreSettings()

// Use memory-only cache
settings.cacheSettings =
MemoryCacheSettings(garbageCollectorSettings: MemoryLRUGCSettings())

// Use persistent disk cache, with 100 MB cache size
settings.cacheSettings = PersistentCacheSettings(sizeBytes: 100 * 1024 * 1024 as NSNumber)

// Any additional options
// ...

// Enable offline data persistence
let db = Firestore.firestore()
db.settings = settings
ViewController.swift
Objective-C
注意：這項產品不適用於 watchOS 和 App Clip 目標。
FIRFirestoreSettings *settings = [[FIRFirestoreSettings alloc] init];

// Use memory-only cache
settings.cacheSettings = [[FIRMemoryCacheSettings alloc]
    initWithGarbageCollectorSettings:[[FIRMemoryLRUGCSettings alloc] init]];

// Use persistent disk cache (default behavior)
// This example uses 100 MB.
settings.cacheSettings = [[FIRPersistentCacheSettings alloc]
    initWithSizeBytes:@(100 * 1024 * 1024)];

// Any additional options
// ...

// Enable offline data persistence
FIRFirestore *db = [FIRFirestore firestore];
db.settings = settings;
ViewController.m

Kotlin+KTX

val settings = firestoreSettings {
    // Use memory cache
    setLocalCacheSettings(memoryCacheSettings {})
    // Use persistent disk cache (default)
    setLocalCacheSettings(persistentCacheSettings {})
}
db.firestoreSettings = settings
DocSnippets.kt

Java

FirebaseFirestoreSettings settings = 
new FirebaseFirestoreSettings.Builder(db.getFirestoreSettings())
    // Use memory-only cache
    .setLocalCacheSettings(MemoryCacheSettings.newBuilder().build())
    // Use persistent disk cache (default)
    .setLocalCacheSettings(PersistentCacheSettings.newBuilder()
                            .build())
    .build();
db.setFirestoreSettings(settings);
DocSnippets.java

Dart

// Apple and Android
db.settings = const Settings(persistenceEnabled: true);

// Web
await db
    .enablePersistence(const PersistenceSettings(synchronizeTabs: true));
firestore.dart

設定快取大小

啟用持續性後，Cloud Firestore 會快取從後端收到的所有文件，以供離線存取。Cloud Firestore 會設定快取大小的預設門檻。超過預設值後，Cloud Firestore 會定期嘗試清理較舊的未使用文件。您可以設定不同的快取大小門檻，或完全停用清除程序：

Web

import { initializeFirestore, CACHE_SIZE_UNLIMITED } from "firebase/firestore";

const firestoreDb = initializeFirestore(app, {
  cacheSizeBytes: CACHE_SIZE_UNLIMITED
});
fs_setup_cache.js

Web

firebase.firestore().settings({
    cacheSizeBytes: firebase.firestore.CACHE_SIZE_UNLIMITED
});
test.firestore.js
Swift
注意：這項產品不適用於 watchOS 和 App Clip 目標。
// The default cache size threshold is 100 MB. Configure "cacheSizeBytes"
// for a different threshold (minimum 1 MB) or set to "FirestoreCacheSizeUnlimited"
// to disable clean-up.
let settings = Firestore.firestore().settings
// Set cache size to 100 MB
settings.cacheSettings = PersistentCacheSettings(sizeBytes: 100 * 1024 * 1024 as NSNumber)
Firestore.firestore().settings = settings
ViewController.swift
Objective-C
注意：這項產品不適用於 watchOS 和 App Clip 目標。
// The default cache size threshold is 100 MB. Configure "cacheSizeBytes"
// for a different threshold (minimum 1 MB) or set to "kFIRFirestoreCacheSizeUnlimited"
// to disable clean-up.
FIRFirestoreSettings *settings = [FIRFirestore firestore].settings;
// Set cache size to 100 MB
settings.cacheSettings =
    [[FIRPersistentCacheSettings alloc] initWithSizeBytes:@(100 * 1024 * 1024)];
[FIRFirestore firestore].settings = settings;
ViewController.m

Kotlin+KTX


// The default cache size threshold is 100 MB. Configure "setCacheSizeBytes"
// for a different threshold (minimum 1 MB) or set to "CACHE_SIZE_UNLIMITED"
// to disable clean-up.
val settings = FirebaseFirestoreSettings.Builder()
        .setCacheSizeBytes(FirebaseFirestoreSettings.CACHE_SIZE_UNLIMITED)
        .build()
db.firestoreSettings = settings

Java


// The default cache size threshold is 100 MB. Configure "setCacheSizeBytes"
// for a different threshold (minimum 1 MB) or set to "CACHE_SIZE_UNLIMITED"
// to disable clean-up.
FirebaseFirestoreSettings settings = new FirebaseFirestoreSettings.Builder()
        .setCacheSizeBytes(FirebaseFirestoreSettings.CACHE_SIZE_UNLIMITED)
        .build();
db.setFirestoreSettings(settings);

Dart

db.settings = const Settings(
  persistenceEnabled: true,
  cacheSizeBytes: Settings.CACHE_SIZE_UNLIMITED,
);
firestore.dart

聆聽離線資料

如果您已啟用離線持久性，當裝置離線時，當本機快取的資料變更，監聽器就會收到監聽事件。您可以聆聽文件、集合和查詢。

如要確認您是從伺服器還是快取接收資料，請在快照事件的 SnapshotMetadata 上使用 fromCache 屬性。如果 fromCache 為 true，表示資料來自快取，且可能過時或不完整。如果 fromCache 為 false，表示資料完整且為最新狀態，且會與伺服器上的最新更新保持一致。

根據預設，如果僅 SnapshotMetadata 有變更，系統就不會觸發事件。如果您依賴 fromCache 值，請在附加監聽處理常式時指定 includeMetadataChanges 監聽選項。

Web

import { collection, onSnapshot, where, query } from "firebase/firestore"; 

const q = query(collection(db, "cities"), where("state", "==", "CA"));
onSnapshot(q, { includeMetadataChanges: true }, (snapshot) => {
    snapshot.docChanges().forEach((change) => {
        if (change.type === "added") {
            console.log("New city: ", change.doc.data());
        }

        const source = snapshot.metadata.fromCache ? "local cache" : "server";
        console.log("Data came from " + source);
    });
});
use_from_cache.js

Web

db.collection("cities").where("state", "==", "CA")
  .onSnapshot({ includeMetadataChanges: true }, (snapshot) => {
      snapshot.docChanges().forEach((change) => {
          if (change.type === "added") {
              console.log("New city: ", change.doc.data());
          }

          var source = snapshot.metadata.fromCache ? "local cache" : "server";
          console.log("Data came from " + source);
      });
  });
test.firestore.js
Swift
注意：這項產品不適用於 watchOS 和 App Clip 目標。
// Listen to metadata updates to receive a server snapshot even if
// the data is the same as the cached data.
db.collection("cities").whereField("state", isEqualTo: "CA")
  .addSnapshotListener(includeMetadataChanges: true) { querySnapshot, error in
    guard let snapshot = querySnapshot else {
      print("Error retreiving snapshot: \(error!)")
      return
    }

    for diff in snapshot.documentChanges {
      if diff.type == .added {
        print("New city: \(diff.document.data())")
      }
    }

    let source = snapshot.metadata.isFromCache ? "local cache" : "server"
    print("Metadata: Data fetched from \(source)")
  }
ViewController.swift
Objective-C
注意：這項產品不適用於 watchOS 和 App Clip 目標。 
// Listen to metadata updates to receive a server snapshot even if
// the data is the same as the cached data.
[[[db collectionWithPath:@"cities"] queryWhereField:@"state" isEqualTo:@"CA"]
    addSnapshotListenerWithIncludeMetadataChanges:YES
    listener:^(FIRQuerySnapshot *snapshot, NSError *error) {
      if (snapshot == nil) {
        NSLog(@"Error retreiving snapshot: %@", error);
        return;
      }
      for (FIRDocumentChange *diff in snapshot.documentChanges) {
        if (diff.type == FIRDocumentChangeTypeAdded) {
          NSLog(@"New city: %@", diff.document.data);
        }
      }

      NSString *source = snapshot.metadata.isFromCache ? @"local cache" : @"server";
      NSLog(@"Metadata: Data fetched from %@", source);
    }];
ViewController.m

Kotlin+KTX

db.collection("cities").whereEqualTo("state", "CA")
    .addSnapshotListener(MetadataChanges.INCLUDE) { querySnapshot, e ->
        if (e != null) {
            Log.w(TAG, "Listen error", e)
            return@addSnapshotListener
        }

        for (change in querySnapshot!!.documentChanges) {
            if (change.type == DocumentChange.Type.ADDED) {
                Log.d(TAG, "New city: ${change.document.data}")
            }

            val source = if (querySnapshot.metadata.isFromCache) {
                "local cache"
            } else {
                "server"
            }
            Log.d(TAG, "Data fetched from $source")
        }
    }
DocSnippets.kt

Java

db.collection("cities").whereEqualTo("state", "CA")
        .addSnapshotListener(MetadataChanges.INCLUDE, new EventListener<QuerySnapshot>() {
            @Override
            public void onEvent(@Nullable QuerySnapshot querySnapshot,
                                @Nullable FirebaseFirestoreException e) {
                if (e != null) {
                    Log.w(TAG, "Listen error", e);
                    return;
                }

                for (DocumentChange change : querySnapshot.getDocumentChanges()) {
                    if (change.getType() == Type.ADDED) {
                        Log.d(TAG, "New city:" + change.getDocument().getData());
                    }

                    String source = querySnapshot.getMetadata().isFromCache() ?
                            "local cache" : "server";
                    Log.d(TAG, "Data fetched from " + source);
                }

            }
        });
DocSnippets.java

Dart

db
    .collection("cities")
    .where("state", isEqualTo: "CA")
    .snapshots(includeMetadataChanges: true)
    .listen((querySnapshot) {
  for (var change in querySnapshot.docChanges) {
    if (change.type == DocumentChangeType.added) {
      final source =
          (querySnapshot.metadata.isFromCache) ? "local cache" : "server";

      print("Data fetched from $source}");
    }
  }
});
firestore.dart

取得離線資料

如果您在裝置離線時取得文件，Cloud Firestore 會從快取傳回資料。

查詢集合時，如果沒有快取的文件，系統會傳回空白結果。擷取特定文件時，系統會改為傳回錯誤。

查詢離線資料

查詢可搭配離線持久性運作。您可以直接取得或監聽，藉此擷取查詢結果，如前面各節所述。您也可以在裝置離線時，針對本機快取的資料建立新的查詢，但查詢一開始只會針對快取的文件執行。

設定離線查詢索引

根據預設，Firestore SDK 會在執行離線查詢時，掃描集合中的所有本機快取文件。在這種預設行為下，如果使用者長時間離線，離線查詢的效能就會受到影響。

啟用永久快取後，您可以允許 SDK 自動建立本機查詢索引，進而改善離線查詢的效能。

自動索引功能預設為停用。應用程式每次啟動時，都必須啟用自動建立索引功能。控制是否啟用自動索引功能，如下所示。

Swift
if let indexManager = Firestore.firestore().persistentCacheIndexManager {
  // Indexing is disabled by default
  indexManager.enableIndexAutoCreation()
} else {
  print("indexManager is nil")
}
Objective-C
PersistentCacheIndexManager *indexManager = [FIRFirestore firestore].persistentCacheIndexManager;
if (indexManager) {
  // Indexing is disabled by default
  [indexManager enableIndexAutoCreation];
}

Kotlin+KTX

// return type: PersistentCacheManager?

Firebase.firestore.persistentCacheIndexManager?.apply {
      // Indexing is disabled by default
      enableIndexAutoCreation()
    } ?: println("indexManager is null")

Java

// return type: @Nullable PersistentCacheIndexManager
PersistentCacheIndexManager indexManager = FirebaseFirestore.getInstance().getPersistentCacheIndexManager();
if (indexManager != null) {
  // Indexing is disabled by default
  indexManager.enableIndexAutoCreation();
}

// If not check indexManager != null, IDE shows warning: Method invocation 'enableIndexAutoCreation' may produce 'NullPointerException' 
FirebaseFirestore.getInstance().getPersistentCacheIndexManager().enableIndexAutoCreation();

啟用自動索引功能後，SDK 會評估哪些集合含有大量的快取文件，並最佳化本機查詢的效能。

SDK 提供刪除查詢索引的方法。

停用及啟用網路存取權

您可以使用下列方法，為 Cloud Firestore 用戶端停用網路存取權。在網路存取權無效的情況下，所有快照事件監聽器和文件要求都會從快取中擷取結果。寫入作業會排入佇列，直到網路存取重新啟用為止。

Web

import { disableNetwork } from "firebase/firestore"; 

await disableNetwork(db);
console.log("Network disabled!");
// Do offline actions
// ...
disable_network.js

Web

firebase.firestore().disableNetwork()
    .then(() => {
        // Do offline actions
        // ...
    });
test.firestore.js
Swift
注意：這項產品不適用於 watchOS 和 App Clip 目標。
Firestore.firestore().disableNetwork { (error) in
  // Do offline things
  // ...
}
ViewController.swift
Objective-C
注意：這項產品不適用於 watchOS 和 App Clip 目標。
[[FIRFirestore firestore] disableNetworkWithCompletion:^(NSError *_Nullable error) {
  // Do offline actions
  // ...
}];
ViewController.m

Kotlin+KTX

db.disableNetwork().addOnCompleteListener {
    // Do offline things
    // ...
}
DocSnippets.kt

Java

db.disableNetwork()
        .addOnCompleteListener(new OnCompleteListener<Void>() {
            @Override
            public void onComplete(@NonNull Task<Void> task) {
                // Do offline things
                // ...
            }
        });
DocSnippets.java

Dart

db.disableNetwork().then((_) {
  // Do offline things
});
firestore.dart

請使用以下方法重新啟用網路存取權：

Web

import { enableNetwork } from "firebase/firestore"; 

await enableNetwork(db);
// Do online actions
// ...
enable_network.js

Web

firebase.firestore().enableNetwork()
    .then(() => {
        // Do online actions
        // ...
    });
test.firestore.js
Swift
注意：這項產品不適用於 watchOS 和 App Clip 目標。
Firestore.firestore().enableNetwork { (error) in
  // Do online things
  // ...
}
ViewController.swift
Objective-C
注意：這項產品不適用於 watchOS 和 App Clip 目標。
[[FIRFirestore firestore] enableNetworkWithCompletion:^(NSError *_Nullable error) {
  // Do online actions
  // ...
}];
ViewController.m

Kotlin+KTX

db.enableNetwork().addOnCompleteListener {
    // Do online things
    // ...
}
DocSnippets.kt

Java

db.enableNetwork()
        .addOnCompleteListener(new OnCompleteListener<Void>() {
            @Override
            public void onComplete(@NonNull Task<Void> task) {
                // Do online things
                // ...
            }
        });
DocSnippets.java

Dart

db.enableNetwork().then((_) {
  // Back online
});
firestore.dart