Cloud Firestore 数据捆绑包

Cloud Firestore 数据捆绑包是您根据 Cloud Firestore 文档和查询快照而构建,并发布在 CDN、托管服务或其他解决方案上的静态数据文件。数据捆绑包中包含您要向客户端应用交付的文档,以及关于生成这些文档的查询的元数据。您可以使用客户端 SDK 通过网络或从本地存储空间下载软件包,之后再将软件包数据加载到 Cloud Firestore 本地缓存。捆绑包加载后,客户端应用可以从本地缓存或后端查询文档。

借助数据捆绑包,您的应用可以更快地加载常见查询的结果,因为启动时文档就已经就绪,无需调用 Cloud Firestore 后端。如果结果是从本地缓存加载的,还可降低访问成本。您无需为查询相同的 100 个初始文档的 100 万个应用实例付费,而只需为将这 100 个文档打包所需的查询付费。

Cloud Firestore 数据捆绑包可与其他 Firebase 后端产品搭配使用。请查看我们提供的集成解决方案,在这种解决方案中,软件包由 Cloud Functions 函数构建并通过 Firebase Hosting 向用户分发。

将捆绑包与您的应用一起使用涉及以下三个步骤:

  1. 使用 Admin SDK 构建捆绑包
  2. 从本地存储空间或从 CDN 分发捆绑包
  3. 在客户端中加载捆绑包

什么是数据捆绑包?

数据软件包是一个由您构建的静态二进制文件,可用于封装一个或多个文档和/或查询快照,您也可以从中提取“命名的查询”。服务器端 SDK 让您可以构建捆绑包,而客户端 SDK 提供了将捆绑包加载到本地缓存的方法,我们将在下文展开讨论。

“命名的查询”是捆绑包特别强大的一个功能。命名的查询是您可以从捆绑包中提取的 Query 对象,提取后您可以立即从缓存或后端查询数据,就像您平常在应用内与 Cloud Firestore 通讯时所做的那样。

在服务器上构建数据捆绑包

利用 Node.js 或 Java Admin SDK,您可以完全控制要在捆绑包中包含哪些内容以及分发它们的方式。

Node.js
var bundleId = "latest-stories";

var bundle = firestore.bundle(bundleId);

var docSnapshot = await firestore.doc('stories/stories').get();
var querySnapshot = await firestore.collection('stories').get();

// Build the bundle
// Note how querySnapshot is named "latest-stories-query"
var bundleBuffer = bundle.add(docSnapshot); // Add a document
                   .add('latest-stories-query', querySnapshot) // Add a named query.
                   .build()
      
Java
Firestore db = FirestoreClient.getFirestore(app);

// Query the 50 latest stories
QuerySnapshot latestStories = db.collection("stories")
    .orderBy("timestamp", Direction.DESCENDING)
    .limit(50)
    .get()
    .get();

// Build the bundle from the query results
FirestoreBundle bundle = db.bundleBuilder("latest-stories")
    .add("latest-stories-query", latestStories)
    .build();
      
Python
from google.cloud import firestore
from google.cloud.firestore_bundle import FirestoreBundle

db = firestore.Client()
bundle = FirestoreBundle("latest-stories")

doc_snapshot = db.collection("stories").document("news-item").get()
query = db.collection("stories")._query()

# Build the bundle
# Note how `query` is named "latest-stories-query"
bundle_buffer: str = bundle.add_document(doc_snapshot).add_named_query(
    "latest-stories-query", query,
).build()
      

分发数据捆绑包

您可以通过从 CDN 分发或从 Cloud Storage 等位置下载的方式,将捆绑包分发到客户端应用。

假设在上一部分中创建的捆绑包已保存到名为 bundle.txt 的文件中,并发布到了服务器上。您可以像分发任何其他资产一样通过网络分发此捆绑包文件,如下方的一个简单 Node.js Express 应用的示例所示。

const fs = require('fs');
const server = require('http').createServer();

server.on('request', (req, res) => {
  const src = fs.createReadStream('./bundle.txt');
  src.pipe(res);
});

server.listen(8000);

在客户端中加载数据捆绑包

您可以从远程服务器提取 Firestore 捆绑包以进行加载,提取方法包括:发出 HTTP 请求、调用 Storage API 或使用任何其他方法来提取网络中的二进制文件。

提取后,您的应用会使用 Cloud Firestore 客户端 SDK 调用 loadBundle 方法,该方法会返回一个任务跟踪对象,让您可以像监控 Promise 的状态一样监控上述过程的完成情况。捆绑包加载任务成功完成后,便可在本地缓存中获取捆绑包内容了。

Web

import { loadBundle, namedQuery, getDocsFromCache } from "firebase/firestore";

async function fetchFromBundle() {
  // Fetch the bundle from Firebase Hosting, if the CDN cache is hit the 'X-Cache'
  // response header will be set to 'HIT'
  const resp = await fetch('/createBundle');

  // Load the bundle contents into the Firestore SDK
  await loadBundle(db, resp.body);

  // Query the results from the cache
  const query = await namedQuery(db, 'latest-stories-query');
  const storiesSnap = await getDocsFromCache(query);

  // Use the results
  // ...
}

Web

// If you are using module bundlers.
import firebase from "firebase/app";
import "firebase/firestore";
import "firebase/firestore/bundle"; // This line enables bundle loading as a side effect.

// ...

async function fetchFromBundle() {
  // Fetch the bundle from Firebase Hosting, if the CDN cache is hit the 'X-Cache'
  // response header will be set to 'HIT'
  const resp = await fetch('/createBundle');

  // Load the bundle contents into the Firestore SDK
  await db.loadBundle(resp.body);

  // Query the results from the cache
  // Note: omitting "source: cache" will query the Firestore backend.
  const query = await db.namedQuery('latest-stories-query');
  const storiesSnap = await query.get({ source: 'cache' });

  // Use the results
  // ...
}
Swift
注意:此产品不适用于 watchOS 和 App Clip 目标。
// Utility function for errors when loading bundles.
func bundleLoadError(reason: String) -> NSError {
  return NSError(domain: "FIRSampleErrorDomain",
                 code: 0,
                 userInfo: [NSLocalizedFailureReasonErrorKey: reason])
}

func fetchRemoteBundle(for firestore: Firestore,
                       from url: URL) async throws -> LoadBundleTaskProgress {
  guard let inputStream = InputStream(url: url) else {
    let error = self.bundleLoadError(reason: "Unable to create stream from the given url: \(url)")
    throw error
  }

  return try await firestore.loadBundle(inputStream)
}

// Fetches a specific named query from the provided bundle.
func loadQuery(named queryName: String,
               fromRemoteBundle bundleURL: URL,
               with store: Firestore) async throws -> Query {
  let _ = try await fetchRemoteBundle(for: store, from: bundleURL)
  if let query = await store.getQuery(named: queryName) {
    return query
  } else {
    throw bundleLoadError(reason: "Could not find query named \(queryName)")
  }
}

// Load a query and fetch its results from a bundle.
func runStoriesQuery() async {
  let queryName = "latest-stories-query"
  let firestore = Firestore.firestore()
  let remoteBundle = URL(string: "https://example.com/createBundle")!

  do {
    let query = try await loadQuery(named: queryName,
                                    fromRemoteBundle: remoteBundle,
                                    with: firestore)
    let snapshot = try await query.getDocuments()
    print(snapshot)
    // handle query results
  } catch {
    print(error)
  }
}
Objective-C
注意:此产品不适用于 watchOS 和 App Clip 目标。
// Utility function for errors when loading bundles.
- (NSError *)bundleLoadErrorWithReason:(NSString *)reason {
  return [NSError errorWithDomain:@"FIRSampleErrorDomain"
                             code:0
                         userInfo:@{NSLocalizedFailureReasonErrorKey: reason}];
}

// Loads a remote bundle from the provided url.
- (void)fetchRemoteBundleForFirestore:(FIRFirestore *)firestore
                              fromURL:(NSURL *)url
                           completion:(void (^)(FIRLoadBundleTaskProgress *_Nullable,
                                                NSError *_Nullable))completion {
  NSInputStream *inputStream = [NSInputStream inputStreamWithURL:url];
  if (inputStream == nil) {
    // Unable to create input stream.
    NSError *error =
        [self bundleLoadErrorWithReason:
            [NSString stringWithFormat:@"Unable to create stream from the given url: %@", url]];
    completion(nil, error);
    return;
  }

  [firestore loadBundleStream:inputStream
                   completion:^(FIRLoadBundleTaskProgress * _Nullable progress,
                                NSError * _Nullable error) {
    if (progress == nil) {
      completion(nil, error);
      return;
    }

    if (progress.state == FIRLoadBundleTaskStateSuccess) {
      completion(progress, nil);
    } else {
      NSError *concreteError =
          [self bundleLoadErrorWithReason:
              [NSString stringWithFormat:
                  @"Expected bundle load to be completed, but got %ld instead",
                  (long)progress.state]];
      completion(nil, concreteError);
    }
    completion(nil, nil);
  }];
}

// Loads a bundled query.
- (void)loadQueryNamed:(NSString *)queryName
   fromRemoteBundleURL:(NSURL *)url
         withFirestore:(FIRFirestore *)firestore
            completion:(void (^)(FIRQuery *_Nullable, NSError *_Nullable))completion {
  [self fetchRemoteBundleForFirestore:firestore
                              fromURL:url
                           completion:^(FIRLoadBundleTaskProgress *progress, NSError *error) {
    if (error != nil) {
      completion(nil, error);
      return;
    }

    [firestore getQueryNamed:queryName completion:^(FIRQuery *query) {
      if (query == nil) {
        NSString *errorReason =
            [NSString stringWithFormat:@"Could not find query named %@", queryName];
        NSError *error = [self bundleLoadErrorWithReason:errorReason];
        completion(nil, error);
        return;
      }
      completion(query, nil);
    }];
  }];
}

- (void)runStoriesQuery {
  NSString *queryName = @"latest-stories-query";
  FIRFirestore *firestore = [FIRFirestore firestore];
  NSURL *bundleURL = [NSURL URLWithString:@"https://example.com/createBundle"];
  [self loadQueryNamed:queryName
   fromRemoteBundleURL:bundleURL
         withFirestore:firestore
            completion:^(FIRQuery *query, NSError *error) {
    // Handle query results
  }];
}

Kotlin+KTX

@Throws(IOException::class)
fun getBundleStream(urlString: String?): InputStream {
    val url = URL(urlString)
    val connection = url.openConnection() as HttpURLConnection
    return connection.inputStream
}

@Throws(IOException::class)
fun fetchFromBundle() {
    val bundleStream = getBundleStream("https://example.com/createBundle")
    val loadTask = db.loadBundle(bundleStream)

    // Chain the following tasks
    // 1) Load the bundle
    // 2) Get the named query from the local cache
    // 3) Execute a get() on the named query
    loadTask.continueWithTask<Query> { task ->
        // Close the stream
        bundleStream.close()

        // Calling .result propagates errors
        val progress = task.getResult(Exception::class.java)

        // Get the named query from the bundle cache
        db.getNamedQuery("latest-stories-query")
    }.continueWithTask { task ->
        val query = task.getResult(Exception::class.java)!!

        // get() the query results from the cache
        query.get(Source.CACHE)
    }.addOnCompleteListener { task ->
        if (!task.isSuccessful) {
            Log.w(TAG, "Bundle loading failed", task.exception)
            return@addOnCompleteListener
        }

        // Get the QuerySnapshot from the bundle
        val storiesSnap = task.result

        // Use the results
        // ...
    }
}

Java

public InputStream getBundleStream(String urlString) throws IOException {
    URL url = new URL(urlString);
    HttpURLConnection connection = (HttpURLConnection) url.openConnection();
    return connection.getInputStream();
}

public void fetchBundleFrom() throws IOException {
    final InputStream bundleStream = getBundleStream("https://example.com/createBundle");
    LoadBundleTask loadTask = db.loadBundle(bundleStream);

    // Chain the following tasks
    // 1) Load the bundle
    // 2) Get the named query from the local cache
    // 3) Execute a get() on the named query
    loadTask.continueWithTask(new Continuation<LoadBundleTaskProgress, Task<Query>>() {
        @Override
        public Task<Query> then(@NonNull Task<LoadBundleTaskProgress> task) throws Exception {
            // Close the stream
            bundleStream.close();

            // Calling getResult() propagates errors
            LoadBundleTaskProgress progress = task.getResult(Exception.class);

            // Get the named query from the bundle cache
            return db.getNamedQuery("latest-stories-query");
        }
    }).continueWithTask(new Continuation<Query, Task<QuerySnapshot>>() {
        @Override
        public Task<QuerySnapshot> then(@NonNull Task<Query> task) throws Exception {
            Query query = task.getResult(Exception.class);

            // get() the query results from the cache
            return query.get(Source.CACHE);
        }
    }).addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
        @Override
        public void onComplete(@NonNull Task<QuerySnapshot> task) {
            if (!task.isSuccessful()) {
                Log.w(TAG, "Bundle loading failed", task.getException());
                return;
            }

            // Get the QuerySnapshot from the bundle
            QuerySnapshot storiesSnap = task.getResult();

            // Use the results
            // ...
        }
    });
}
C++
db->LoadBundle("bundle_name", [](const LoadBundleTaskProgress& progress) {
  switch(progress.state()) {
    case LoadBundleTaskProgress::State::kError: {
      // The bundle load has errored. Handle the error in the returned future.
      return;
    }
    case LoadBundleTaskProgress::State::kInProgress: {
      std::cout << "Bytes loaded from bundle: " << progress.bytes_loaded()
                << std::endl;
      break;
    }
    case LoadBundleTaskProgress::State::kSuccess: {
      std::cout << "Bundle load succeeeded" << std::endl;
      break;
    }
  }
}).OnCompletion([db](const Future<LoadBundleTaskProgress>& future) {
  if (future.error() != Error::kErrorOk) {
    // Handle error...
    return;
  }

  const std::string& query_name = "latest_stories_query";
  db->NamedQuery(query_name).OnCompletion([](const Future<Query>& query_future){
    if (query_future.error() != Error::kErrorOk) {
      // Handle error...
      return;
    }

    const Query* query = query_future.result();
    query->Get().OnCompletion([](const Future<QuerySnapshot> &){
      // ...
    });
  });
});

请注意,如果从不到 30 分钟前构建的捆绑包中加载命名的查询,那么等到您利用查询从后端(而不是缓存)读取数据后,您只需为更新文档以匹配后端存储的数据所需的数据库读取付费;也就是说,您只需为增量付费。

后续步骤