是否可以使用新的Firebase数据库Cloud Firestore来计算一个集合有多少项?
如果是,我该怎么做?
是否可以使用新的Firebase数据库Cloud Firestore来计算一个集合有多少项?
如果是,我该怎么做?
当前回答
除了上面我的npm包adv-firestore-functions,你还可以使用firestore规则来强制一个好的计数器:
Firestore规则
function counter() {
let docPath = /databases/$(database)/documents/_counters/$(request.path[3]);
let afterCount = getAfter(docPath).data.count;
let beforeCount = get(docPath).data.count;
let addCount = afterCount == beforeCount + 1;
let subCount = afterCount == beforeCount - 1;
let newId = getAfter(docPath).data.docId == request.path[4];
let deleteDoc = request.method == 'delete';
let createDoc = request.method == 'create';
return (newId && subCount && deleteDoc) || (newId && addCount && createDoc);
}
function counterDoc() {
let doc = request.path[4];
let docId = request.resource.data.docId;
let afterCount = request.resource.data.count;
let beforeCount = resource.data.count;
let docPath = /databases/$(database)/documents/$(doc)/$(docId);
let createIdDoc = existsAfter(docPath) && !exists(docPath);
let deleteIdDoc = !existsAfter(docPath) && exists(docPath);
let addCount = afterCount == beforeCount + 1;
let subCount = afterCount == beforeCount - 1;
return (createIdDoc && addCount) || (deleteIdDoc && subCount);
}
像这样使用它们:
match /posts/{document} {
allow read;
allow update;
allow create: if counter();
allow delete: if counter();
}
match /_counters/{document} {
allow read;
allow write: if counterDoc();
}
前端
用以下函数替换你的set和delete函数:
set
async setDocWithCounter(
ref: DocumentReference<DocumentData>,
data: {
[x: string]: any;
},
options: SetOptions): Promise<void> {
// counter collection
const counterCol = '_counters';
const col = ref.path.split('/').slice(0, -1).join('/');
const countRef = doc(this.afs, counterCol, col);
const countSnap = await getDoc(countRef);
const refSnap = await getDoc(ref);
// don't increase count if edit
if (refSnap.exists()) {
await setDoc(ref, data, options);
// increase count
} else {
const batch = writeBatch(this.afs);
batch.set(ref, data, options);
// if count exists
if (countSnap.exists()) {
batch.update(countRef, {
count: increment(1),
docId: ref.id
});
// create count
} else {
// will only run once, should not use
// for mature apps
const colRef = collection(this.afs, col);
const colSnap = await getDocs(colRef);
batch.set(countRef, {
count: colSnap.size + 1,
docId: ref.id
});
}
batch.commit();
}
}
删除
async delWithCounter(
ref: DocumentReference<DocumentData>
): Promise<void> {
// counter collection
const counterCol = '_counters';
const col = ref.path.split('/').slice(0, -1).join('/');
const countRef = doc(this.afs, counterCol, col);
const countSnap = await getDoc(countRef);
const batch = writeBatch(this.afs);
// if count exists
batch.delete(ref);
if (countSnap.exists()) {
batch.update(countRef, {
count: increment(-1),
docId: ref.id
});
}
/*
if ((countSnap.data() as any).count == 1) {
batch.delete(countRef);
}*/
batch.commit();
}
更多信息请看这里…
J
其他回答
这使用计数来创建数字唯一ID。在我的使用中,我将永远不会递减,即使需要ID的文档被删除。
在需要唯一数值的集合创建时
用一个文档指定一个集合appData,只设置.doc id 在firebase防火控制台中将uniqueNumericIDAmount设置为0 使用doc.data()。uniqueNumericIDAmount + 1作为唯一的数字id 更新appData收集uniqueNumericIDAmount与firebase.firestore.FieldValue.increment(1)
firebase
.firestore()
.collection("appData")
.doc("only")
.get()
.then(doc => {
var foo = doc.data();
foo.id = doc.id;
// your collection that needs a unique ID
firebase
.firestore()
.collection("uniqueNumericIDs")
.doc(user.uid)// user id in my case
.set({// I use this in login, so this document doesn't
// exist yet, otherwise use update instead of set
phone: this.state.phone,// whatever else you need
uniqueNumericID: foo.uniqueNumericIDAmount + 1
})
.then(() => {
// upon success of new ID, increment uniqueNumericIDAmount
firebase
.firestore()
.collection("appData")
.doc("only")
.update({
uniqueNumericIDAmount: firebase.firestore.FieldValue.increment(
1
)
})
.catch(err => {
console.log(err);
});
})
.catch(err => {
console.log(err);
});
});
和许多问题一样,答案是——视情况而定。
在前端处理大量数据时应该非常小心。除了让你的前端感觉迟钝之外,Firestore还会向你收取每百万次读取60美元的费用。
小型收藏(少于100份文件)
小心使用-前端用户体验可能会受到影响
在前端处理这个应该没问题,只要你没有对这个返回的数组做太多的逻辑处理。
db.collection('...').get().then(snap => {
size = snap.size // will return the collection size
});
中等藏书(100至1000份)
小心使用- Firestore读取调用可能会花费很多
在前端处理这个问题是不可行的,因为它有很大的可能会降低用户系统的速度。我们应该处理这个逻辑服务器端,只返回大小。
这种方法的缺点是您仍然在调用Firestore读取(等于您的集合的大小),从长远来看,这最终可能会使您的成本超过预期。
云功能:
db.collection('...').get().then(snap => {
res.status(200).send({length: snap.size});
});
前端:
yourHttpClient.post(yourCloudFunctionUrl).toPromise().then(snap => {
size = snap.length // will return the collection size
})
大量的收集(1000+文档)
最具可扩展性的解决方案
FieldValue.increment ()
截至2019年4月,Firestore现在允许增量计数器,完全原子,无需事先读取数据。这确保了即使同时从多个源进行更新(以前使用事务解决)也能获得正确的计数器值,同时还减少了执行的数据库读取次数。
通过监听任何删除或创建的文档,我们可以向数据库中的计数字段添加或删除。
参见firestore文档-分布式计数器 或者看看杰夫·德莱尼的《数据聚合》。他的指南对于任何使用AngularFire的人来说都是非常棒的,但他的课程也应该适用于其他框架。
云功能:
export const documentWriteListener = functions.firestore
.document('collection/{documentUid}')
.onWrite((change, context) => {
if (!change.before.exists) {
// New document Created : add one to count
db.doc(docRef).update({ numberOfDocs: FieldValue.increment(1) });
} else if (change.before.exists && change.after.exists) {
// Updating existing document : Do nothing
} else if (!change.after.exists) {
// Deleting document : subtract one from count
db.doc(docRef).update({ numberOfDocs: FieldValue.increment(-1) });
}
return;
});
现在在前端,你可以查询这个numberOfDocs字段来获得集合的大小。
除了上面我的npm包adv-firestore-functions,你还可以使用firestore规则来强制一个好的计数器:
Firestore规则
function counter() {
let docPath = /databases/$(database)/documents/_counters/$(request.path[3]);
let afterCount = getAfter(docPath).data.count;
let beforeCount = get(docPath).data.count;
let addCount = afterCount == beforeCount + 1;
let subCount = afterCount == beforeCount - 1;
let newId = getAfter(docPath).data.docId == request.path[4];
let deleteDoc = request.method == 'delete';
let createDoc = request.method == 'create';
return (newId && subCount && deleteDoc) || (newId && addCount && createDoc);
}
function counterDoc() {
let doc = request.path[4];
let docId = request.resource.data.docId;
let afterCount = request.resource.data.count;
let beforeCount = resource.data.count;
let docPath = /databases/$(database)/documents/$(doc)/$(docId);
let createIdDoc = existsAfter(docPath) && !exists(docPath);
let deleteIdDoc = !existsAfter(docPath) && exists(docPath);
let addCount = afterCount == beforeCount + 1;
let subCount = afterCount == beforeCount - 1;
return (createIdDoc && addCount) || (deleteIdDoc && subCount);
}
像这样使用它们:
match /posts/{document} {
allow read;
allow update;
allow create: if counter();
allow delete: if counter();
}
match /_counters/{document} {
allow read;
allow write: if counterDoc();
}
前端
用以下函数替换你的set和delete函数:
set
async setDocWithCounter(
ref: DocumentReference<DocumentData>,
data: {
[x: string]: any;
},
options: SetOptions): Promise<void> {
// counter collection
const counterCol = '_counters';
const col = ref.path.split('/').slice(0, -1).join('/');
const countRef = doc(this.afs, counterCol, col);
const countSnap = await getDoc(countRef);
const refSnap = await getDoc(ref);
// don't increase count if edit
if (refSnap.exists()) {
await setDoc(ref, data, options);
// increase count
} else {
const batch = writeBatch(this.afs);
batch.set(ref, data, options);
// if count exists
if (countSnap.exists()) {
batch.update(countRef, {
count: increment(1),
docId: ref.id
});
// create count
} else {
// will only run once, should not use
// for mature apps
const colRef = collection(this.afs, col);
const colSnap = await getDocs(colRef);
batch.set(countRef, {
count: colSnap.size + 1,
docId: ref.id
});
}
batch.commit();
}
}
删除
async delWithCounter(
ref: DocumentReference<DocumentData>
): Promise<void> {
// counter collection
const counterCol = '_counters';
const col = ref.path.split('/').slice(0, -1).join('/');
const countRef = doc(this.afs, counterCol, col);
const countSnap = await getDoc(countRef);
const batch = writeBatch(this.afs);
// if count exists
batch.delete(ref);
if (countSnap.exists()) {
batch.update(countRef, {
count: increment(-1),
docId: ref.id
});
}
/*
if ((countSnap.data() as any).count == 1) {
batch.delete(countRef);
}*/
batch.commit();
}
更多信息请看这里…
J
在2020年,Firebase SDK中还没有这个功能,但Firebase扩展(Beta)中有,不过设置和使用起来相当复杂……
合理的方法
帮手……(创建/删除似乎是多余的,但比onUpdate便宜)
export const onCreateCounter = () => async (
change,
context
) => {
const collectionPath = change.ref.parent.path;
const statsDoc = db.doc("counters/" + collectionPath);
const countDoc = {};
countDoc["count"] = admin.firestore.FieldValue.increment(1);
await statsDoc.set(countDoc, { merge: true });
};
export const onDeleteCounter = () => async (
change,
context
) => {
const collectionPath = change.ref.parent.path;
const statsDoc = db.doc("counters/" + collectionPath);
const countDoc = {};
countDoc["count"] = admin.firestore.FieldValue.increment(-1);
await statsDoc.set(countDoc, { merge: true });
};
export interface CounterPath {
watch: string;
name: string;
}
出口消防钩
export const Counters: CounterPath[] = [
{
name: "count_buildings",
watch: "buildings/{id2}"
},
{
name: "count_buildings_subcollections",
watch: "buildings/{id2}/{id3}/{id4}"
}
];
Counters.forEach(item => {
exports[item.name + '_create'] = functions.firestore
.document(item.watch)
.onCreate(onCreateCounter());
exports[item.name + '_delete'] = functions.firestore
.document(item.watch)
.onDelete(onDeleteCounter());
});
在行动
将跟踪构建根集合和所有子集合。
在/counters/ root路径下
现在收集计数将自动更新,最终!如果需要计数,只需使用收集路径并在其前面加上计数器即可。
const collectionPath = 'buildings/138faicnjasjoa89/buildingContacts';
const collectionCount = await db
.doc('counters/' + collectionPath)
.get()
.then(snap => snap.get('count'));
限制
由于此方法使用单个数据库和文档,因此每个计数器的Firestore约束为每秒更新1次。它最终将是一致的,但在添加/删除大量文档的情况下,计数器将落后于实际收集计数。
截至2022年10月,Firestore在客户端sdk上引入了count()方法。现在您可以在没有下载的情况下计算查询。
对于1000份文件,它将收取你阅读1份文件的费用。
网络(v9)
Firebase 9.11.0介绍:
const collectionRef = collection(db, "cities");
const snapshot = await getCountFromServer(collectionRef);
console.log('count: ', snapshot.data().count);
Web V8
不可用。
节点(管理)
const collectionRef = db.collection('cities');
const snapshot = await collectionRef.count().get();
console.log(snapshot.data().count);
Android (Kotlin)
在firestore v24.4.0 (BoM 31.0.0)引入:
val query = db.collection("cities")
val countQuery = query.count()
countQuery.get(AggregateSource.SERVER).addOnCompleteListener { task ->
if (task.isSuccessful) {
val snapshot = task.result
Log.d(TAG, "Count: ${snapshot.count}")
} else {
Log.d(TAG, "Count failed: ", task.getException())
}
}
苹果平台(Swift)
Firestore v10.0.0引入:
do {
let query = db.collection("cities")
let countQuery = query.countAggregateQuery
let snapshot = try await countQuery.aggregation(source: AggregateSource.server)
print(snapshot.count)
} catch {
print(error)
}