feat: Add Aggregate method to Query

firestore/src/common/query.cc

@@ -113,6 +113,12 @@ AggregateQuery Query::Count() const {
   return internal_->Count();
 }
 
+AggregateQuery Query::Aggregate(const AggregateField& aggregate_field) const {
+  if (!internal_) return {};
+  return internal_->Aggregate(aggregate_field);
+}
+
+
 Query Query::Where(const Filter& filter) const {
   if (!internal_) return {};
   if (filter.IsEmpty()) {

firestore/src/include/firebase/firestore/query.h

@@ -160,6 +160,22 @@ class Query {
    */
   virtual AggregateQuery Count() const;
 
+  /**
+   * @brief Returns a query that calculates the specified aggregation over the
+   * documents in the result set of this query.
+   *
+   * The returned query, when executed, performs the specified aggregation
+   * without downloading the actual document data.
+   *
+   * Using the returned query to calculate aggregations is efficient because
+   * only the aggregation result, not the documents' data, is downloaded. This
+   * can be useful for aggregations over large result sets.
+   *
+   * @param aggregate_field The field to aggregate on.
+   * @return An aggregate query that performs the specified aggregation.
+   */
+  virtual AggregateQuery Aggregate(const AggregateField& aggregate_field) const;
+
   /**
    * @brief Creates and returns a new Query with the additional filter.
    *

firestore/src/main/query_main.cc

@@ -99,6 +99,11 @@ Future<QuerySnapshot> QueryInternal::Get(Source source) {
 
 AggregateQuery QueryInternal::Count() { return MakePublic(query_.Count()); }
 
+AggregateQuery QueryInternal::Aggregate(const AggregateField& aggregate_field) {
+  // TODO: Implement Aggregate
+  // return MakePublic(aggregate_field);
+}
+
 Query QueryInternal::Where(const Filter& filter) const {
   SIMPLE_HARD_ASSERT(!filter.IsEmpty());
   core::Filter core_filter =

firestore/src/main/query_main.h

@@ -60,6 +60,8 @@ class QueryInternal {
 
   AggregateQuery Count();
 
+  AggregateQuery Aggregate(const AggregateField& aggregate_field);
+
   ListenerRegistration AddSnapshotListener(
       MetadataChanges metadata_changes, EventListener<QuerySnapshot>* listener);