feat: Add Aggregate method to QueryInternal

Author: KKimj

firestore/src/android/query_android.cc

@@ -162,6 +162,13 @@ AggregateQuery QueryInternal::Count() const {
   return firestore_->NewAggregateQuery(env, aggregate_query);
 }
 
+AggregateQuery QueryInternal::Aggregate(const FieldPath& field) const {
+  Env env = GetEnv();
+  Local<Object> java_field = FieldPathConverter::Create(env, field);
+  Local<Object> aggregate_query = env.Call(obj_, kAggregate, java_field);
+  return firestore_->NewAggregateQuery(env, aggregate_query);
+}
+
 Query QueryInternal::Where(const firebase::firestore::Filter& filter) const {
   Env env = GetEnv();
   Local<Object> query = env.Call(obj_, kWhere, filter.internal_->ToJava());

firestore/src/android/query_android.h

@@ -71,6 +71,15 @@ class QueryInternal : public Wrapper {
    */
   virtual AggregateQuery Count() const;
 
+  /**
+   * @brief Returns a query that calculates the specified aggregation over the
+   * documents in the result set of this query.
+   *
+   * @param[in] aggregate_field The aggregation field.
+   * @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.
    *