Cloud Firestore 支持讀取和寫入數據的原子操作。在一組原子操作中,要么所有操作都成功,要么都不應用。 Cloud Firestore 中有兩種類型的原子操作:
每個事務或批量寫入最多可以寫入 500 個文檔。有關與寫入相關的其他限制,請參閱配額和限制。
使用事務更新數據
使用 Cloud Firestore 客戶端庫,您可以將多個操作組合到一個事務中。當您想要根據字段的當前值或其他字段的值更新字段的值時,事務很有用。
事務由任意數量的get()
操作和後跟任意數量的寫操作組成,例如set()
、 update()
或delete()
。在並發編輯的情況下,Cloud Firestore 會再次運行整個事務。例如,如果一個事務讀取文檔,而另一個客戶端修改了這些文檔中的任何一個,Cloud Firestore 會重試該事務。此功能可確保事務在最新且一致的數據上運行。
事務從不部分應用寫入。所有寫入都在成功事務結束時執行。
使用事務時,請注意:
- 讀操作必須在寫操作之前進行。
- 如果並發編輯影響事務讀取的文檔,調用事務的函數(事務函數)可能會運行多次。
- 交易功能不應直接修改應用程序狀態。
- 當客戶端離線時,交易將失敗。
以下示例顯示如何創建和運行事務:
Web modular API
import { runTransaction } from "firebase/firestore"; try { await runTransaction(db, async (transaction) => { const sfDoc = await transaction.get(sfDocRef); if (!sfDoc.exists()) { throw "Document does not exist!"; } const newPopulation = sfDoc.data().population + 1; transaction.update(sfDocRef, { population: newPopulation }); }); console.log("Transaction successfully committed!"); } catch (e) { console.log("Transaction failed: ", e); }
Web namespaced API
// Create a reference to the SF doc. var sfDocRef = db.collection("cities").doc("SF"); // Uncomment to initialize the doc. // sfDocRef.set({ population: 0 }); return db.runTransaction((transaction) => { // This code may get re-run multiple times if there are conflicts. return transaction.get(sfDocRef).then((sfDoc) => { if (!sfDoc.exists) { throw "Document does not exist!"; } // Add one person to the city population. // Note: this could be done without a transaction // by updating the population using FieldValue.increment() var newPopulation = sfDoc.data().population + 1; transaction.update(sfDocRef, { population: newPopulation }); }); }).then(() => { console.log("Transaction successfully committed!"); }).catch((error) => { console.log("Transaction failed: ", error); });
迅速
let sfReference = db.collection("cities").document("SF") db.runTransaction({ (transaction, errorPointer) -> Any? in let sfDocument: DocumentSnapshot do { try sfDocument = transaction.getDocument(sfReference) } catch let fetchError as NSError { errorPointer?.pointee = fetchError return nil } guard let oldPopulation = sfDocument.data()?["population"] as? Int else { let error = NSError( domain: "AppErrorDomain", code: -1, userInfo: [ NSLocalizedDescriptionKey: "Unable to retrieve population from snapshot \(sfDocument)" ] ) errorPointer?.pointee = error return nil } // Note: this could be done without a transaction // by updating the population using FieldValue.increment() transaction.updateData(["population": oldPopulation + 1], forDocument: sfReference) return nil }) { (object, error) in if let error = error { print("Transaction failed: \(error)") } else { print("Transaction successfully committed!") } }
目標-C
FIRDocumentReference *sfReference = [[self.db collectionWithPath:@"cities"] documentWithPath:@"SF"]; [self.db runTransactionWithBlock:^id (FIRTransaction *transaction, NSError **errorPointer) { FIRDocumentSnapshot *sfDocument = [transaction getDocument:sfReference error:errorPointer]; if (*errorPointer != nil) { return nil; } if (![sfDocument.data[@"population"] isKindOfClass:[NSNumber class]]) { *errorPointer = [NSError errorWithDomain:@"AppErrorDomain" code:-1 userInfo:@{ NSLocalizedDescriptionKey: @"Unable to retreive population from snapshot" }]; return nil; } NSInteger oldPopulation = [sfDocument.data[@"population"] integerValue]; // Note: this could be done without a transaction // by updating the population using FieldValue.increment() [transaction updateData:@{ @"population": @(oldPopulation + 1) } forDocument:sfReference]; return nil; } completion:^(id result, NSError *error) { if (error != nil) { NSLog(@"Transaction failed: %@", error); } else { NSLog(@"Transaction successfully committed!"); } }];
Kotlin+KTX
val sfDocRef = db.collection("cities").document("SF") db.runTransaction { transaction -> val snapshot = transaction.get(sfDocRef) // Note: this could be done without a transaction // by updating the population using FieldValue.increment() val newPopulation = snapshot.getDouble("population")!! + 1 transaction.update(sfDocRef, "population", newPopulation) // Success null }.addOnSuccessListener { Log.d(TAG, "Transaction success!") } .addOnFailureListener { e -> Log.w(TAG, "Transaction failure.", e) }
Java
final DocumentReference sfDocRef = db.collection("cities").document("SF"); db.runTransaction(new Transaction.Function<Void>() { @Override public Void apply(@NonNull Transaction transaction) throws FirebaseFirestoreException { DocumentSnapshot snapshot = transaction.get(sfDocRef); // Note: this could be done without a transaction // by updating the population using FieldValue.increment() double newPopulation = snapshot.getDouble("population") + 1; transaction.update(sfDocRef, "population", newPopulation); // Success return null; } }).addOnSuccessListener(new OnSuccessListener<Void>() { @Override public void onSuccess(Void aVoid) { Log.d(TAG, "Transaction success!"); } }) .addOnFailureListener(new OnFailureListener() { @Override public void onFailure(@NonNull Exception e) { Log.w(TAG, "Transaction failure.", e); } });
Dart
final sfDocRef = db.collection("cities").doc("SF"); db.runTransaction((transaction) async { final snapshot = await transaction.get(sfDocRef); // Note: this could be done without a transaction // by updating the population using FieldValue.increment() final newPopulation = snapshot.get("population") + 1; transaction.update(sfDocRef, {"population": newPopulation}); }).then( (value) => print("DocumentSnapshot successfully updated!"), onError: (e) => print("Error updating document $e"), );
爪哇
Python
Python
C++
DocumentReference sf_doc_ref = db->Collection("cities").Document("SF"); db->RunTransaction([sf_doc_ref](Transaction& transaction, std::string& out_error_message) -> Error { Error error = Error::kErrorOk; DocumentSnapshot snapshot = transaction.Get(sf_doc_ref, &error, &out_error_message); // Note: this could be done without a transaction by updating the // population using FieldValue::Increment(). std::int64_t new_population = snapshot.Get("population").integer_value() + 1; transaction.Update( sf_doc_ref, {{"population", FieldValue::Integer(new_population)}}); return Error::kErrorOk; }).OnCompletion([](const Future<void>& future) { if (future.error() == Error::kErrorOk) { std::cout << "Transaction success!" << std::endl; } else { std::cout << "Transaction failure: " << future.error_message() << std::endl; } });
節點.js
去
PHP
統一
DocumentReference cityRef = db.Collection("cities").Document("SF"); db.RunTransactionAsync(transaction => { return transaction.GetSnapshotAsync(cityRef).ContinueWith((snapshotTask) => { DocumentSnapshot snapshot = snapshotTask.Result; long newPopulation = snapshot.GetValue<long>("Population") + 1; Dictionary<string, object> updates = new Dictionary<string, object> { { "Population", newPopulation} }; transaction.Update(cityRef, updates); }); });
C#
紅寶石
從交易中傳遞信息
不要在您的事務函數中修改應用程序狀態。這樣做會引入並發問題,因為事務函數可以運行多次並且不能保證在 UI 線程上運行。相反,將您需要的信息傳遞到您的交易功能之外。以下示例建立在前面的示例之上,以顯示如何將信息傳遞出事務:
Web modular API
import { doc, runTransaction } from "firebase/firestore"; // Create a reference to the SF doc. const sfDocRef = doc(db, "cities", "SF"); try { const newPopulation = await runTransaction(db, async (transaction) => { const sfDoc = await transaction.get(sfDocRef); if (!sfDoc.exists()) { throw "Document does not exist!"; } const newPop = sfDoc.data().population + 1; if (newPop <= 1000000) { transaction.update(sfDocRef, { population: newPop }); return newPop; } else { return Promise.reject("Sorry! Population is too big"); } }); console.log("Population increased to ", newPopulation); } catch (e) { // This will be a "population is too big" error. console.error(e); }
Web namespaced API
// Create a reference to the SF doc. var sfDocRef = db.collection("cities").doc("SF"); db.runTransaction((transaction) => { return transaction.get(sfDocRef).then((sfDoc) => { if (!sfDoc.exists) { throw "Document does not exist!"; } var newPopulation = sfDoc.data().population + 1; if (newPopulation <= 1000000) { transaction.update(sfDocRef, { population: newPopulation }); return newPopulation; } else { return Promise.reject("Sorry! Population is too big."); } }); }).then((newPopulation) => { console.log("Population increased to ", newPopulation); }).catch((err) => { // This will be an "population is too big" error. console.error(err); });
迅速
let sfReference = db.collection("cities").document("SF") db.runTransaction({ (transaction, errorPointer) -> Any? in let sfDocument: DocumentSnapshot do { try sfDocument = transaction.getDocument(sfReference) } catch let fetchError as NSError { errorPointer?.pointee = fetchError return nil } guard let oldPopulation = sfDocument.data()?["population"] as? Int else { let error = NSError( domain: "AppErrorDomain", code: -1, userInfo: [ NSLocalizedDescriptionKey: "Unable to retrieve population from snapshot \(sfDocument)" ] ) errorPointer?.pointee = error return nil } // Note: this could be done without a transaction // by updating the population using FieldValue.increment() let newPopulation = oldPopulation + 1 guard newPopulation <= 1000000 else { let error = NSError( domain: "AppErrorDomain", code: -2, userInfo: [NSLocalizedDescriptionKey: "Population \(newPopulation) too big"] ) errorPointer?.pointee = error return nil } transaction.updateData(["population": newPopulation], forDocument: sfReference) return newPopulation }) { (object, error) in if let error = error { print("Error updating population: \(error)") } else { print("Population increased to \(object!)") } }
目標-C
FIRDocumentReference *sfReference = [[self.db collectionWithPath:@"cities"] documentWithPath:@"SF"]; [self.db runTransactionWithBlock:^id (FIRTransaction *transaction, NSError **errorPointer) { FIRDocumentSnapshot *sfDocument = [transaction getDocument:sfReference error:errorPointer]; if (*errorPointer != nil) { return nil; } if (![sfDocument.data[@"population"] isKindOfClass:[NSNumber class]]) { *errorPointer = [NSError errorWithDomain:@"AppErrorDomain" code:-1 userInfo:@{ NSLocalizedDescriptionKey: @"Unable to retreive population from snapshot" }]; return nil; } NSInteger population = [sfDocument.data[@"population"] integerValue]; population++; if (population >= 1000000) { *errorPointer = [NSError errorWithDomain:@"AppErrorDomain" code:-2 userInfo:@{ NSLocalizedDescriptionKey: @"Population too big" }]; return @(population); } [transaction updateData:@{ @"population": @(population) } forDocument:sfReference]; return nil; } completion:^(id result, NSError *error) { if (error != nil) { NSLog(@"Transaction failed: %@", error); } else { NSLog(@"Population increased to %@", result); } }];
Kotlin+KTX
val sfDocRef = db.collection("cities").document("SF") db.runTransaction { transaction -> val snapshot = transaction.get(sfDocRef) val newPopulation = snapshot.getDouble("population")!! + 1 if (newPopulation <= 1000000) { transaction.update(sfDocRef, "population", newPopulation) newPopulation } else { throw FirebaseFirestoreException( "Population too high", FirebaseFirestoreException.Code.ABORTED, ) } }.addOnSuccessListener { result -> Log.d(TAG, "Transaction success: $result") }.addOnFailureListener { e -> Log.w(TAG, "Transaction failure.", e) }
Java
final DocumentReference sfDocRef = db.collection("cities").document("SF"); db.runTransaction(new Transaction.Function<Double>() { @Override public Double apply(@NonNull Transaction transaction) throws FirebaseFirestoreException { DocumentSnapshot snapshot = transaction.get(sfDocRef); double newPopulation = snapshot.getDouble("population") + 1; if (newPopulation <= 1000000) { transaction.update(sfDocRef, "population", newPopulation); return newPopulation; } else { throw new FirebaseFirestoreException("Population too high", FirebaseFirestoreException.Code.ABORTED); } } }).addOnSuccessListener(new OnSuccessListener<Double>() { @Override public void onSuccess(Double result) { Log.d(TAG, "Transaction success: " + result); } }) .addOnFailureListener(new OnFailureListener() { @Override public void onFailure(@NonNull Exception e) { Log.w(TAG, "Transaction failure.", e); } });
Dart
final sfDocRef = db.collection("cities").doc("SF"); db.runTransaction((transaction) { return transaction.get(sfDocRef).then((sfDoc) { final newPopulation = sfDoc.get("population") + 1; transaction.update(sfDocRef, {"population": newPopulation}); return newPopulation; }); }).then( (newPopulation) => print("Population increased to $newPopulation"), onError: (e) => print("Error updating document $e"), );
爪哇
Python
Python
C++
// This is not yet supported.
節點.js
去
PHP
統一
DocumentReference cityRef = db.Collection("cities").Document("SF"); db.RunTransactionAsync(transaction => { return transaction.GetSnapshotAsync(cityRef).ContinueWith((task) => { long newPopulation = task.Result.GetValue<long>("Population") + 1; if (newPopulation <= 1000000) { Dictionary<string, object> updates = new Dictionary<string, object> { { "Population", newPopulation} }; transaction.Update(cityRef, updates); return true; } else { return false; } }); }).ContinueWith((transactionResultTask) => { if (transactionResultTask.Result) { Console.WriteLine("Population updated successfully."); } else { Console.WriteLine("Sorry! Population is too big."); } });
C#
紅寶石
交易失敗
事務可能因以下原因而失敗:
- 事務包含寫操作之後的讀操作。讀取操作必須始終在任何寫入操作之前進行。
- 事務讀取在事務外修改的文檔。在這種情況下,事務會自動再次運行。事務重試次數有限。
該事務超過了 10 MiB 的最大請求大小。
事務大小取決於事務修改的文檔和索引條目的大小。對於刪除操作,這包括目標文檔的大小和響應操作刪除的索引條目的大小。
失敗的事務會返回一個錯誤,並且不會向數據庫寫入任何內容。您不需要回滾事務; Cloud Firestore 會自動執行此操作。
批量寫入
如果您不需要讀取操作集中的任何文檔,則可以將多個寫入操作作為包含set()
、 update()
或delete()
操作的任意組合的單個批處理來執行。一批寫入以原子方式完成,並且可以寫入多個文檔。以下示例顯示瞭如何構建和提交寫入批處理:
Web modular API
import { writeBatch, doc } from "firebase/firestore"; // Get a new write batch const batch = writeBatch(db); // Set the value of 'NYC' const nycRef = doc(db, "cities", "NYC"); batch.set(nycRef, {name: "New York City"}); // Update the population of 'SF' const sfRef = doc(db, "cities", "SF"); batch.update(sfRef, {"population": 1000000}); // Delete the city 'LA' const laRef = doc(db, "cities", "LA"); batch.delete(laRef); // Commit the batch await batch.commit();
Web namespaced API
// Get a new write batch var batch = db.batch(); // Set the value of 'NYC' var nycRef = db.collection("cities").doc("NYC"); batch.set(nycRef, {name: "New York City"}); // Update the population of 'SF' var sfRef = db.collection("cities").doc("SF"); batch.update(sfRef, {"population": 1000000}); // Delete the city 'LA' var laRef = db.collection("cities").doc("LA"); batch.delete(laRef); // Commit the batch batch.commit().then(() => { // ... });
迅速
// Get new write batch let batch = db.batch() // Set the value of 'NYC' let nycRef = db.collection("cities").document("NYC") batch.setData([:], forDocument: nycRef) // Update the population of 'SF' let sfRef = db.collection("cities").document("SF") batch.updateData(["population": 1000000 ], forDocument: sfRef) // Delete the city 'LA' let laRef = db.collection("cities").document("LA") batch.deleteDocument(laRef) // Commit the batch batch.commit() { err in if let err = err { print("Error writing batch \(err)") } else { print("Batch write succeeded.") } }
目標-C
// Get new write batch FIRWriteBatch *batch = [self.db batch]; // Set the value of 'NYC' FIRDocumentReference *nycRef = [[self.db collectionWithPath:@"cities"] documentWithPath:@"NYC"]; [batch setData:@{} forDocument:nycRef]; // Update the population of 'SF' FIRDocumentReference *sfRef = [[self.db collectionWithPath:@"cities"] documentWithPath:@"SF"]; [batch updateData:@{ @"population": @1000000 } forDocument:sfRef]; // Delete the city 'LA' FIRDocumentReference *laRef = [[self.db collectionWithPath:@"cities"] documentWithPath:@"LA"]; [batch deleteDocument:laRef]; // Commit the batch [batch commitWithCompletion:^(NSError * _Nullable error) { if (error != nil) { NSLog(@"Error writing batch %@", error); } else { NSLog(@"Batch write succeeded."); } }];
Kotlin+KTX
val nycRef = db.collection("cities").document("NYC") val sfRef = db.collection("cities").document("SF") val laRef = db.collection("cities").document("LA") // Get a new write batch and commit all write operations db.runBatch { batch -> // Set the value of 'NYC' batch.set(nycRef, City()) // Update the population of 'SF' batch.update(sfRef, "population", 1000000L) // Delete the city 'LA' batch.delete(laRef) }.addOnCompleteListener { // ... }
Java
// Get a new write batch WriteBatch batch = db.batch(); // Set the value of 'NYC' DocumentReference nycRef = db.collection("cities").document("NYC"); batch.set(nycRef, new City()); // Update the population of 'SF' DocumentReference sfRef = db.collection("cities").document("SF"); batch.update(sfRef, "population", 1000000L); // Delete the city 'LA' DocumentReference laRef = db.collection("cities").document("LA"); batch.delete(laRef); // Commit the batch batch.commit().addOnCompleteListener(new OnCompleteListener<Void>() { @Override public void onComplete(@NonNull Task<Void> task) { // ... } });
Dart
// Get a new write batch final batch = db.batch(); // Set the value of 'NYC' var nycRef = db.collection("cities").doc("NYC"); batch.set(nycRef, {"name": "New York City"}); // Update the population of 'SF' var sfRef = db.collection("cities").doc("SF"); batch.update(sfRef, {"population": 1000000}); // Delete the city 'LA' var laRef = db.collection("cities").doc("LA"); batch.delete(laRef); // Commit the batch batch.commit().then((_) { // ... });
爪哇
Python
Python
C++
// Get a new write batch WriteBatch batch = db->batch(); // Set the value of 'NYC' DocumentReference nyc_ref = db->Collection("cities").Document("NYC"); batch.Set(nyc_ref, {}); // Update the population of 'SF' DocumentReference sf_ref = db->Collection("cities").Document("SF"); batch.Update(sf_ref, {{"population", FieldValue::Integer(1000000)}}); // Delete the city 'LA' DocumentReference la_ref = db->Collection("cities").Document("LA"); batch.Delete(la_ref); // Commit the batch batch.Commit().OnCompletion([](const Future<void>& future) { if (future.error() == Error::kErrorOk) { std::cout << "Write batch success!" << std::endl; } else { std::cout << "Write batch failure: " << future.error_message() << std::endl; } });
節點.js
去
PHP
統一
WriteBatch batch = db.StartBatch(); // Set the data for NYC DocumentReference nycRef = db.Collection("cities").Document("NYC"); Dictionary<string, object> nycData = new Dictionary<string, object> { { "name", "New York City" } }; batch.Set(nycRef, nycData); // Update the population for SF DocumentReference sfRef = db.Collection("cities").Document("SF"); Dictionary<string, object> updates = new Dictionary<string, object> { { "Population", 1000000} }; batch.Update(sfRef, updates); // Delete LA DocumentReference laRef = db.Collection("cities").Document("LA"); batch.Delete(laRef); // Commit the batch batch.CommitAsync();
C#
紅寶石
一次批量寫入最多可以包含 500 個操作。批次中的每個操作都單獨計入您的 Cloud Firestore 使用量。
與事務一樣,批量寫入是原子的。與事務不同,批量寫入不需要確保讀取的文檔保持未修改狀態,從而減少失敗案例。它們不受重試或因重試次數過多而失敗的影響。即使用戶的設備處於離線狀態,批處理寫入也會執行。
原子操作的數據驗證
對於移動/網絡客戶端庫,您可以使用Cloud Firestore 安全規則驗證數據。您可以確保相關文檔始終以原子方式更新,並且始終作為事務或批量寫入的一部分。使用getAfter()
安全規則函數在一組操作完成後但在 Cloud Firestore 提交操作之前訪問和驗證文檔的狀態。
例如,假設cities
示例的數據庫也包含一個countries
集合。每個country
文檔都使用last_updated
字段來跟踪與該國家/地區相關的任何城市的上次更新時間。以下安全規則要求對city
文檔的更新也必須自動更新相關國家的last_updated
字段:
service cloud.firestore { match /databases/{database}/documents { // If you update a city doc, you must also // update the related country's last_updated field. match /cities/{city} { allow write: if request.auth != null && getAfter( /databases/$(database)/documents/countries/$(request.resource.data.country) ).data.last_updated == request.time; } match /countries/{country} { allow write: if request.auth != null; } } }
安全規則限制
在事務或批量寫入的安全規則中,除了批處理中每個單個文檔操作的正常 10 次調用限制之外,整個原子操作的文檔訪問調用限制為 20 次。
例如,考慮聊天應用程序的以下規則:
service cloud.firestore { match /databases/{db}/documents { function prefix() { return /databases/{db}/documents; } match /chatroom/{roomId} { allow read, write: if request.auth != null && roomId in get(/$(prefix())/users/$(request.auth.uid)).data.chats || exists(/$(prefix())/admins/$(request.auth.uid)); } match /users/{userId} { allow read, write: if request.auth != null && request.auth.uid == userId || exists(/$(prefix())/admins/$(request.auth.uid)); } match /admins/{userId} { allow read, write: if request.auth != null && exists(/$(prefix())/admins/$(request.auth.uid)); } } }
下面的片段說明了用於一些數據訪問模式的文檔訪問調用的數量:
// 0 document access calls used, because the rules evaluation short-circuits // before the exists() call is invoked. db.collection('user').doc('myuid').get(...); // 1 document access call used. The maximum total allowed for this call // is 10, because it is a single document request. db.collection('chatroom').doc('mygroup').get(...); // Initializing a write batch... var batch = db.batch(); // 2 document access calls used, 10 allowed. var group1Ref = db.collection("chatroom").doc("group1"); batch.set(group1Ref, {msg: "Hello, from Admin!"}); // 1 document access call used, 10 allowed. var newUserRef = db.collection("users").doc("newuser"); batch.update(newUserRef, {"lastSignedIn": new Date()}); // 1 document access call used, 10 allowed. var removedAdminRef = db.collection("admin").doc("otheruser"); batch.delete(removedAdminRef); // The batch used a total of 2 + 1 + 1 = 4 document access calls, out of a total // 20 allowed. batch.commit();
有關如何解決由大量寫入和批量寫入引起的延遲問題、重疊事務爭用導致的錯誤以及其他問題的更多信息,請考慮查看故障排除頁面。