使用聚合查询汇总数据（续1）

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") .where("capital", isEqualTo: true) .aggregate(sum("population")) .get() .then( (res) => print(res.getAverage("population")), onError: (e) => print("Error completing: $e"), );

firestore.dart

##### Java

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

##### Node.js

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

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

##### Python

collection_ref = client.collection("users") query = collection_ref.where(filter=FieldFilter("people", "==", "Matthew")) aggregate_query = aggregation.AggregationQuery(query)

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).Limit(5)

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 } ```