feat(firestore): add missing aggregates

packages/dart_firebase_admin/README.md

@@ -203,8 +203,8 @@ print(user.data()?['age']);
 | query.limitToLast                                | ✅  |
 | query.offset                                     | ✅  |
 | query.count()                                    | ✅  |
-| query.sum()                                      | ❌  |
-| query.average()                                  | ❌  |
+| query.sum()                                      | ✅  |
+| query.average()                                  | ✅  |
 | querySnapshot.docs                               | ✅  |
 | querySnapshot.readTime                           | ✅  |
 | documentSnapshots.data                           | ✅  |

packages/dart_firebase_admin/lib/src/google_cloud_firestore/document.dart

@@ -179,7 +179,7 @@ class DocumentSnapshot<T> {
   ///   }
   /// });
   /// ```
-  bool get exists => this._fieldsProto != null;
+  bool get exists => _fieldsProto != null;
 
   /// Retrieves all fields in the document as an object. Returns 'undefined' if
   /// the document doesn't exist.
@@ -196,7 +196,7 @@ class DocumentSnapshot<T> {
   /// });
   /// ```
   T? data() {
-    final fieldsProto = this._fieldsProto;
+    final fieldsProto = _fieldsProto;
     final fields = fieldsProto?.fields;
     if (fields == null || fieldsProto == null) return null;
 
@@ -245,7 +245,7 @@ class DocumentSnapshot<T> {
   }
 
   firestore1.Value? _protoField(FieldPath field) {
-    final fieldsProto = this._fieldsProto?.fields;
+    final fieldsProto = _fieldsProto?.fields;
     if (fieldsProto == null) return null;
     var fields = fieldsProto;
 
@@ -300,11 +300,11 @@ class _DocumentSnapshotBuilder<T> {
 
   DocumentSnapshot<T> build() {
     assert(
-      (this.fieldsProto != null) == (this.createTime != null),
+      (this.fieldsProto != null) == (createTime != null),
       'Create time should be set iff document exists.',
     );
     assert(
-      (this.fieldsProto != null) == (this.updateTime != null),
+      (this.fieldsProto != null) == (updateTime != null),
       'Update time should be set iff document exists.',
     );
 

packages/dart_firebase_admin/lib/src/google_cloud_firestore/document_reader.dart

@@ -90,7 +90,7 @@ class _DocumentReader<T> {
         DocumentSnapshot<DocumentData>? documentSnapshot;
 
         if (response.transaction?.isNotEmpty ?? false) {
-          this._retrievedTransactionId = response.transaction;
+          _retrievedTransactionId = response.transaction;
         }
 
         final found = response.found;

packages/dart_firebase_admin/lib/src/google_cloud_firestore/path.dart

@@ -53,12 +53,12 @@ abstract class _Path<T extends _Path<Object?>> implements Comparable<_Path<T>> {
 
   /// Checks whether the current path is a prefix of the specified path.
   bool _isPrefixOf(_Path<T> other) {
-    if (other.segments.length < this.segments.length) {
+    if (other.segments.length < segments.length) {
       return false;
     }
 
-    for (var i = 0; i < this.segments.length; i++) {
-      if (this.segments[i] != other.segments[i]) {
+    for (var i = 0; i < segments.length; i++) {
+      if (segments[i] != other.segments[i]) {
         return false;
       }
     }
@@ -74,8 +74,8 @@ abstract class _Path<T extends _Path<Object?>> implements Comparable<_Path<T>> {
       if (compare != 0) return compare;
     }
 
-    if (this.segments.length < other.segments.length) return -1;
-    if (this.segments.length > other.segments.length) return 1;
+    if (segments.length < other.segments.length) return -1;
+    if (segments.length > other.segments.length) return 1;
 
     return 0;
   }