Aggregations

The library supports the Core aggregation functions count, sum and avg over the documents a query matches. Each result field is named by a.field(alias), and its operator is chosen with .count(), .count_up_to(limit), .sum(field) or .avg(field):

use firestore::*;
use serde::{Deserialize, Serialize};
#[derive(Debug, Clone, Deserialize, Serialize)]
struct MyAggTestStructure { counter: usize }
const TEST_COLLECTION_NAME: &str = "test";
async fn example(db: FirestoreDb) -> Result<(), Box<dyn std::error::Error + Send + Sync>> {
let objs: Vec<MyAggTestStructure> = db
    .fluent()
    .select()
    .from(TEST_COLLECTION_NAME)
    .aggregate(|a| a.fields([a.field(path!(MyAggTestStructure::counter)).count()]))
    .obj()
    .query()
    .await?;
let _ = objs;
Ok(())
}

Several aggregations run in one query, each under its own alias:

use firestore::*;
use serde::{Deserialize, Serialize};
#[derive(Debug, Clone, Deserialize, Serialize)]
struct Totals { count: usize, total: i64, average: f64 }
const TEST_COLLECTION_NAME: &str = "test";
async fn example(db: FirestoreDb) -> Result<(), Box<dyn std::error::Error + Send + Sync>> {
let totals: Vec<Totals> = db
    .fluent()
    .select()
    .from(TEST_COLLECTION_NAME)
    .aggregate(|a| {
        a.fields([
            a.field(path!(Totals::count)).count(),
            a.field(path!(Totals::total)).sum("n"),
            a.field(path!(Totals::average)).avg("n"),
        ])
    })
    .obj()
    .query()
    .await?;
let _ = totals;
Ok(())
}

An aggregation result is not a stored document, so it has no document name, see Query and write semantics. Grouped aggregations, by a field, are a pipeline feature on the Enterprise edition, see Pipeline aggregations and joins.

On the Enterprise edition

Core aggregations and transactions behave the same on both editions. An aggregation whose filter needs a composite index fails on Standard with FAILED_PRECONDITION, and runs as a scan on Enterprise, see Querying.