使用聚合查询汇总数据

聚合查询会处理多个索引条目中的数据，然后返回单个摘要值。

Cloud Firestore 支持以下聚合查询：

• count()
• sum()
• average()

Cloud Firestore 会计算聚合结果，并仅将结果传回您的应用。与在应用中执行完整查询并计算聚合相比，聚合查询可以节省计费的文档读取和传输的字节数所产生的费用。

聚合查询依赖于您的查询已在使用的现有索引配置，并且会根据扫描到的索引条目数量按比例进行扩缩。随着聚合中的项数增加，延迟时间也会变长。

使用 count() 聚合

通过 count() 聚合查询，您可以确定集合或查询中的文档数量。

如需详细了解示例数据，请参阅获取数据。

以下 count() 聚合会返回 cities 集合中的城市总数。

Web

const coll = collection(db, "cities");
const snapshot = await getCountFromServer(coll);
console.log('count: ', snapshot.data().count);

count_aggregate_collection.js

Swift

注意：此产品不适用于 watchOS 和 App Clip 目标。

let query = db.collection("cities")
let countQuery = query.count
do {
  let snapshot = try await countQuery.getAggregation(source: .server)
  print(snapshot.count)
} catch {
  print(error)
}

ViewController.swift

Objective-C

注意：此产品不适用于 watchOS 和 App Clip 目标。

FIRCollectionReference *query = [self.db collectionWithPath:@"cities"];
[query.count aggregationWithSource:FIRAggregateSourceServer
                        completion:^(FIRAggregateQuerySnapshot *snapshot,
                                     NSError *error) {
    if (error != nil) {
        NSLog(@"Error fetching count: %@", error);
    } else {
        NSLog(@"Cities count: %@", snapshot.count);
    }
}];

ViewController.m

Java

Query query = db.collection("cities");
AggregateQuery countQuery = query.count();
countQuery.get(AggregateSource.SERVER).addOnCompleteListener(new OnCompleteListener<AggregateQuerySnapshot>() {
    @Override
    public void onComplete(@NonNull Task<AggregateQuerySnapshot> task) {
        if (task.isSuccessful()) {
            // Count fetched successfully
            AggregateQuerySnapshot snapshot = task.getResult();
            Log.d(TAG, "Count: " + snapshot.getCount());
        } else {
            Log.d(TAG, "Count failed: ", task.getException());
        }
    }
});

DocSnippets.java

Kotlin

val query = db.collection("cities")
val countQuery = query.count()
countQuery.get(AggregateSource.SERVER).addOnCompleteListener { task ->
    if (task.isSuccessful) {
        // Count fetched successfully
        val snapshot = task.result
        Log.d(TAG, "Count: ${snapshot.count}")
    } else {
        Log.d(TAG, "Count failed: ", task.getException())
    }
}

DocSnippets.kt

Dart

// Returns number of documents in users collection
db.collection("cities").count().get().then(
      (res) => print(res.count),
      onError: (e) => print("Error completing: $e"),
    );

firestore.dart

Go

package firestore

import (
    "context"
    "errors"
    "fmt"
    "io"

    "cloud.google.com/go/firestore"
    firestorepb "cloud.google.com/go/firestore/apiv1/firestorepb"
)

func createCountQuery(w io.Writer, projectID string) error {

    // Instantiate the client
    ctx := context.Background()
    client, err := firestore.NewClient(ctx, projectID)
    if err != nil {
        return err
    }
    defer client.Close()

    collection := client.Collection("users")
    query := collection.Where("born", ">", 1850)

    // `alias` argument--"all"--provides a key for accessing the aggregate query
    // results. The alias value must be unique across all aggregation aliases in
    // an aggregation query and must conform to allowed Document field names.
    //
    // See https://cloud.google.com/firestore/docs/reference/rpc/google.firestore.v1#document for details.
    aggregationQuery := query.NewAggregationQuery().WithCount("all")
    results, err := aggregationQuery.Get(ctx)
    if err != nil {
        return err
    }

    count, ok := results["all"]
    if !ok {
        return errors.New("firestore: couldn't get alias for COUNT from results")
    }

    countValue := count.(*firestorepb.Value)
    fmt.Fprintf(w, "Number of results from query: %d\n", countValue.GetIntegerValue())
    return nil
}

aggregate_query_count.go

Java

CollectionReference collection = db.collection("cities");
AggregateQuerySnapshot snapshot = collection.count().get().get();
System.out.println("Count: " + snapshot.getCount());

Node.js

const collectionRef = db.collection('cities');
const snapshot = await collectionRef.count().get();
console.log(snapshot.data().count);

Python

from google.cloud import firestore
from google.cloud.firestore_v1 import aggregation
from google.cloud.firestore_v1.base_query import FieldFilter

def create_count_query(project_id: str) -> None:
    """Builds an aggregate query that returns the number of results in the query.

    Arguments:
      project_id: your Google Cloud Project ID
    """
    client = firestore.Client(project=project_id)

    collection_ref = client.collection("users")
    query = collection_ref.where(filter=FieldFilter("born", ">", 1800))
    aggregate_query = aggregation.AggregationQuery(query)

    # `alias` to provides a key for accessing the aggregate query results
    aggregate_query.count(alias="all")

    results = aggregate_query.get()
    for result in results:
        print(f"Alias of results from query: {result[0].alias}")
        print(f"Number of results from query: {result[0].value}")

aggregate_query_count.py

count() 聚合会考虑查询的所有过滤条件以及所有 limit 子句。

Web

const coll = collection(db, "cities");
const q = query(coll, where("state", "==", "CA"));
const snapshot = await getCountFromServer(q);
console.log('count: ', snapshot.data().count);

count_aggregate_query.js

Swift

注意：此产品不适用于 watchOS 和 App Clip 目标。

let query = db.collection("cities").whereField("state", isEqualTo: "CA")
let countQuery = query.count
do {
  let snapshot = try await countQuery.getAggregation(source: .server)
  print(snapshot.count)
} catch {
  print(error)
}

ViewController.swift

Objective-C

注意：此产品不适用于 watchOS 和 App Clip 目标。

FIRQuery *query =
    [[self.db collectionWithPath:@"cities"]
                 queryWhereField:@"state"
                       isEqualTo:@"CA"];
[query.count aggregationWithSource:FIRAggregateSourceServer
                        completion:^(FIRAggregateQuerySnapshot *snapshot,
                                      NSError *error) {
    if (error != nil) {
        NSLog(@"Error fetching count: %@", error);
    } else {
        NSLog(@"Cities count: %@", snapshot.count);
    }
}];

ViewController.m

Java

Query query = db.collection("cities").whereEqualTo("state", "CA");
AggregateQuery countQuery = query.count();
countQuery.get(AggregateSource.SERVER).addOnCompleteListener(new OnCompleteListener<AggregateQuerySnapshot>() {
    @Override
    public void onComplete(@NonNull Task<AggregateQuerySnapshot> task) {
        if (task.isSuccessful()) {
            // Count fetched successfully
            AggregateQuerySnapshot snapshot = task.getResult();
            Log.d(TAG, "Count: " + snapshot.getCount());
        } else {
            Log.d(TAG, "Count failed: ", task.getException());
        }
    }
});

DocSnippets.java

Kotlin

val query = db.collection("cities").whereEqualTo("state", "CA")
val countQuery = query.count()
countQuery.get(AggregateSource.SERVER).addOnCompleteListener { task ->
    if (task.isSuccessful) {
        // Count fetched successfully
        val snapshot = task.result
        Log.d(TAG, "Count: ${snapshot.count}")
    } else {
        Log.d(TAG, "Count failed: ", task.getException())
    }
}

DocSnippets.kt

Dart

// This also works with collection queries.
db.collection("cities").where("capital", isEqualTo: 10).count().get().then(
      (res) => print(res.count),
      onError: (e) => print("Error completing: $e"),
    );

firestore.dart

Go

package firestore

import (
    "context"
    "errors"
    "fmt"
    "io"

    "cloud.google.com/go/firestore"
    firestorepb "cloud.google.com/go/firestore/apiv1/firestorepb"
)

func createCountQuery(w io.Writer, projectID string) error {

    // Instantiate the client
    ctx := context.Background()
    client, err := firestore.NewClient(ctx, projectID)
    if err != nil {
        return err
    }
    defer client.Close()

    collection := client.Collection("users")
    query := collection.Where("born", ">", 1850)

    // `alias` argument--"all"--provides a key for accessing the aggregate query
    // results. The alias value must be unique across all aggregation aliases in
    // an aggregation query and must conform to allowed Document field names.
    //
    // See https://cloud.google.com/firestore/docs/reference/rpc/google.firestore.v1#document for details.
    aggregationQuery := query.NewAggregationQuery().WithCount("all")
    results, err := aggregationQuery.Get(ctx)
    if err != nil {
        return err
    }

    count, ok := results["all"]
    if !ok {
        return errors.New("firestore: couldn't get alias for COUNT from results")
    }

    countValue := count.(*firestorepb.Value)
    fmt.Fprintf(w, "Number of results from query: %d\n", countValue.GetIntegerValue())
    return nil
}

aggregate_query_count.go

Java

CollectionReference collection = db.collection("cities");
Query query = collection.whereEqualTo("state", "CA");
AggregateQuerySnapshot snapshot = query.count().get().get();
System.out.println("Count: " + snapshot.getCount());

Node.js

const collectionRef = db.collection('cities');
const query = collectionRef.where('state', '==', 'CA');
const snapshot = await query.count().get();
console.log(snapshot.data().count);

Python

from google.cloud import firestore
from google.cloud.firestore_v1 import aggregation
from google.cloud.firestore_v1.base_query import FieldFilter

def create_count_query(project_id: str) -> None:
    """Builds an aggregate query that returns the number of results in the query.

    Arguments:
      project_id: your Google Cloud Project ID
    """
    client = firestore.Client(project=project_id)

    collection_ref = client.collection("users")
    query = collection_ref.where(filter=FieldFilter("born", ">", 1800))
    aggregate_query = aggregation.AggregationQuery(query)

    # `alias` to provides a key for accessing the aggregate query results
    aggregate_query.count(alias="all")

    results = aggregate_query.get()
    for result in results:
        print(f"Alias of results from query: {result[0].alias}")
        print(f"Number of results from query: {result[0].value}")

aggregate_query_count.py

使用 sum() 聚合

使用 sum() 聚合可返回与给定查询匹配的数值的总和，例如：

Web

const coll = collection(firestore, 'cities');
const snapshot = await getAggregateFromServer(coll, {
  totalPopulation: sum('population')
});

console.log('totalPopulation: ', snapshot.data().totalPopulation);

Swift

注意：此产品不适用于 watchOS 和 App Clip 目标。

let query = db.collection("cities")
let aggregateQuery = query.aggregate([AggregateField.sum("population")])
do {
  let snapshot = try await aggregateQuery.getAggregation(source: .server)
  print(snapshot.get(AggregateField.sum("population")))
} catch {
  print(error)
}

ViewController.swift

Objective-C

注意：此产品不适用于 watchOS 和 App Clip 目标。

FIRQuery *query = [self.db collectionWithPath:@"cities"];
FIRAggregateQuery *aggregateQuery = [query aggregate:@[
    [FIRAggregateField aggregateFieldForSumOfField:@"population"]]];
[aggregateQuery aggregationWithSource:FIRAggregateSourceServer
                           completion:^(FIRAggregateQuerySnapshot *snapshot,
                                        NSError *error) {
    if (error != nil) {
        NSLog(@"Error fetching aggregate: %@", error);
    } else {
        NSLog(@"Sum: %@", [snapshot valueForAggregateField:[FIRAggregateField aggregateFieldForSumOfField:@"population"]]);
    }
}];

ViewController.m

Java

Query query = db.collection("cities");
AggregateQuery aggregateQuery = query.aggregate(AggregateField.sum("population"));
aggregateQuery.get(AggregateSource.SERVER).addOnCompleteListener(new OnCompleteListener<AggregateQuerySnapshot>() {
    @Override
    public void onComplete(@NonNull Task<AggregateQuerySnapshot> task) {
        if (task.isSuccessful()) {
            // Aggregate fetched successfully
            AggregateQuerySnapshot snapshot = task.getResult();
            Log.d(TAG, "Sum: " + snapshot.get(AggregateField.sum("population")));
        } else {
            Log.d(TAG, "Aggregation failed: ", task.getException());
        }
    }
});

DocSnippets.java

Kotlin

val query = db.collection("cities")
val aggregateQuery = query.aggregate(AggregateField.sum("population"))
aggregateQuery.get(AggregateSource.SERVER).addOnCompleteListener { task ->
    if (task.isSuccessful) {
        // Aggregate fetched successfully
        val snapshot = task.result
        Log.d(TAG, "Sum: ${snapshot.get(AggregateField.sum("population"))}")
    } else {
        Log.d(TAG, "Aggregate failed: ", task.getException())
    }
}

DocSnippets.kt

Dart

db.collection("cities").aggregate(sum("population")).get().then(
      (res) => print(res.getAverage("population")),
      onError: (e) => print("Error completing: $e"),
    );

firestore.dart

Java

collection = db.collection("cities");
snapshot = collection.aggregate(sum("population")).get().get();
System.out.println("Sum: " + snapshot.get(sum("population")));

Node.js

const coll = firestore.collection('cities');
const sumAggregateQuery = coll.aggregate({
         totalPopulation: AggregateField.sum('population'),
       });

const snapshot = await sumAggregateQuery.get();
console.log('totalPopulation: ', snapshot.data().totalPopulation);

Python

collection_ref = client.collection("users")
aggregate_query = aggregation.AggregationQuery(collection_ref)

aggregate_query.sum("coins", alias="sum")

results = aggregate_query.get()
for result in results:
    print(f"Alias of results from query: {result[0].alias}")
    print(f"Sum of results from query: {result[0].value}")

Go

func createSumQuery(w io.Writer, projectID string) error {
  ctx := context.Background()
  client, err := firestore.NewClient(ctx, projectID)
  if err != nil {
    return err
  }
  defer client.Close()

  collection := client.Collection("users")
  query := collection.Where("born", ">", 1850)

  aggregationQuery := query.NewAggregationQuery().WithSum("coins", "sum_coins")
  results, err := aggregationQuery.Get(ctx)
  if err != nil {
    return err
  }

  sum, ok := results["sum_coins"]
  if !ok {
    return errors.New("firestore: couldn't get alias for SUM from results")
  }

  sumValue := sum.(*firestorepb.Value)
  fmt.Fprintf(w, "Sum of results from query: %d\n", sumValue.GetIntegerValue())
  return nil
}

sum() 聚合会考虑查询的所有过滤条件以及所有限制子句，例如：

Web

const coll = collection(firestore, 'cities');
const q = query(coll, where('capital', '==', true));
const snapshot = await getAggregateFromServer(q, {
  totalPopulation: sum('population')
});

console.log('totalPopulation: ', snapshot.data().totalPopulation);

Swift

注意：此产品不适用于 watchOS 和 App Clip 目标。

let query = db.collection("cities").whereField("capital", isEqualTo: true)
let aggregateQuery = query.aggregate([AggregateField.sum("population")])
do {
  let snapshot = try await aggregateQuery.getAggregation(source: .server)
  print(snapshot.get(AggregateField.sum("population")))
} catch {
  print(error)
}

ViewController.swift

Objective-C

注意：此产品不适用于 watchOS 和 App Clip 目标。

FIRQuery *query = [[self.db collectionWithPath:@"cities"]
                   queryWhereFilter:[FIRFilter filterWhereField:@"capital" isEqualTo:@YES]];
FIRAggregateQuery *aggregateQuery = [query aggregate:@[
    [FIRAggregateField aggregateFieldForSumOfField:@"population"]]];
[aggregateQuery aggregationWithSource:FIRAggregateSourceServer
                           completion:^(FIRAggregateQuerySnapshot *snapshot,
                                        NSError *error) {
    if (error != nil) {
        NSLog(@"Error fetching aggregate: %@", error);
    } else {
        NSLog(@"Sum: %@", [snapshot valueForAggregateField:[FIRAggregateField aggregateFieldForSumOfField:@"population"]]);
    }
}];

ViewController.m

Java

Query query = db.collection("cities").whereEqualTo("capital", true);
AggregateQuery aggregateQuery = query.aggregate(AggregateField.sum("population"));
aggregateQuery.get(AggregateSource.SERVER).addOnCompleteListener(new OnCompleteListener<AggregateQuerySnapshot>() {
    @Override
    public void onComplete(@NonNull Task<AggregateQuerySnapshot> task) {
        if (task.isSuccessful()) {
            // Aggregate fetched successfully
            AggregateQuerySnapshot snapshot = task.getResult();
            Log.d(TAG, "Sum: " + snapshot.get(AggregateField.sum("population")));
        } else {
            Log.d(TAG, "Aggregation failed: ", task.getException());
        }
    }
});

DocSnippets.java

Kotlin

``` val query = db.collection("cities").whereEqualTo("capital", true) val aggregateQuery = query.aggregate(AggregateField.sum("population")) aggregateQuery.get(AggregateSource.SERVER).addOnCompleteListener { task ->