Add private function that returns a query's hash code.

firestore/integration_test_internal/src/query_test.cc

@@ -71,6 +71,20 @@ std::vector<MapFieldValue> AllDocsExcept(
 
 }  // namespace
 
+size_t QueryHash(const Query& query) { return query.Hash(); }
+
+TEST_F(QueryTest, TestHashCode) {
+  CollectionReference collection =
+      Collection({{"a", {{"k", FieldValue::String("a")}}},
+                  {"b", {{"k", FieldValue::String("b")}}}});
+  Query query1 =
+      collection.Limit(2).OrderBy("sort", Query::Direction::kAscending);
+  Query query2 =
+      collection.Limit(2).OrderBy("sort", Query::Direction::kDescending);
+  EXPECT_NE(QueryHash(query1), QueryHash(query2));
+  EXPECT_EQ(QueryHash(query1), QueryHash(query1));
+}
+
 TEST_F(QueryTest, TestLimitQueries) {
   CollectionReference collection =
       Collection({{"a", {{"k", FieldValue::String("a")}}},

firestore/src/android/query_android.cc

@@ -130,6 +130,7 @@ Method<Object> kAddSnapshotListener(
     "Lcom/google/firebase/firestore/MetadataChanges;"
     "Lcom/google/firebase/firestore/EventListener;)"
     "Lcom/google/firebase/firestore/ListenerRegistration;");
+Method<int32_t> kHashCode("hashCode", "()I");
 
 }  // namespace
 
@@ -139,7 +140,7 @@ void QueryInternal::Initialize(jni::Loader& loader) {
       kGreaterThan, kGreaterThanOrEqualTo, kArrayContains, kArrayContainsAny,
       kIn, kNotIn, kOrderBy, kLimit, kLimitToLast, kStartAtSnapshot, kStartAt,
       kStartAfterSnapshot, kStartAfter, kEndBeforeSnapshot, kEndBefore,
-      kEndAtSnapshot, kEndAt, kGet, kAddSnapshotListener);
+      kEndAtSnapshot, kEndAt, kGet, kAddSnapshotListener, kHashCode);
 }
 
 Firestore* QueryInternal::firestore() {
@@ -346,6 +347,11 @@ Local<Array<Object>> QueryInternal::ConvertFieldValues(
   return result;
 }
 
+size_t QueryInternal::Hash() const {
+  Env env = GetEnv();
+  return env.Call(obj_, kHashCode);
+}
+
 bool operator==(const QueryInternal& lhs, const QueryInternal& rhs) {
   return jni::EqualityCompareJni(lhs, rhs);
 }

firestore/src/android/query_android.h

@@ -379,6 +379,8 @@ class QueryInternal : public Wrapper {
       EventListener<QuerySnapshot>* listener,
       bool passing_listener_ownership = false);
 
+  size_t Hash() const;
+
  protected:
   PromiseFactory<AsyncFn> promises_;
 

firestore/src/common/query.cc

@@ -302,6 +302,11 @@ ListenerRegistration Query::AddSnapshotListener(
                                         firebase::Move(callback));
 }
 
+size_t Query::Hash() const {
+  if (!internal_) return {};
+  return internal_->Hash();
+}
+
 bool operator==(const Query& lhs, const Query& rhs) {
   return EqualityCompare(lhs.internal_, rhs.internal_);
 }

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

@@ -650,7 +650,10 @@ class Query {
   bool is_valid() const { return internal_ != nullptr; }
 
  private:
+  size_t Hash() const;
+
   friend bool operator==(const Query& lhs, const Query& rhs);
+  friend size_t QueryHash(const Query& query);
 
   friend class FirestoreInternal;
   friend class QueryInternal;

firestore/src/main/query_main.h

@@ -145,6 +145,8 @@ class QueryInternal {
     return WithBound(BoundPosition::kEndAt, values);
   }
 
+  size_t Hash() const { return query_.Hash(); }
+
   friend bool operator==(const QueryInternal& lhs, const QueryInternal& rhs);
 
  protected: