feat: COUNT API added

google-cloud-firestore/src/main/java/com/google/cloud/firestore/AggregateDemo.java

@@ -0,0 +1,45 @@
+/*
+ * Copyright 2022 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *       http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.cloud.firestore;
+
+import java.util.Objects;
+
+public class AggregateDemo {
+
+  public static void Demo1_CountOfDocumentsInACollection(Firestore db) throws Exception {
+    Query query = db.collection("games").document("halo").collection("players");
+    AggregateQuerySnapshot snapshot = query.count().get().get();
+    assertEqual(snapshot.getCount(), 5_000_000);
+  }
+
+  public static void Demo2_LimitNumberOfDocumentsScannedWithLimit(Firestore db) throws Exception {
+    // Limit the work / documents scanned by restricting underlying query.
+    Query query = db.collection("games").document("halo").collection("players").limit(1000);
+    AggregateQuerySnapshot snapshot = query.count().get().get();
+    assertEqual(snapshot.getCount(), 1000);
+  }
+
+  private static void assertEqual(Long num1, Long num2) {
+    if (!Objects.equals(num1, num2)) {
+      throw new AssertionError("num1!=num2");
+    }
+  }
+
+  private static void assertEqual(Long num1, int num2) {
+    assertEqual(num1, Long.valueOf(num2));
+  }
+}

google-cloud-firestore/src/main/java/com/google/cloud/firestore/AggregateQuery.java

@@ -0,0 +1,35 @@
+/*
+ * Copyright 2022 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *       http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.cloud.firestore;
+
+import com.google.api.core.ApiFuture;
+import javax.annotation.Nonnull;
+
+public interface AggregateQuery {
+
+  @Nonnull
+  Query getQuery();
+
+  @Nonnull
+  ApiFuture<AggregateQuerySnapshot> get();
+
+  @Override
+  int hashCode();
+
+  @Override
+  boolean equals(Object obj);
+}

google-cloud-firestore/src/main/java/com/google/cloud/firestore/AggregateQuerySnapshot.java

@@ -0,0 +1,41 @@
+/*
+ * Copyright 2022 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *       http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.cloud.firestore;
+
+import com.google.cloud.Timestamp;
+
+import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
+
+public interface AggregateQuerySnapshot {
+
+  @Nonnull
+  AggregateQuery getQuery();
+
+  @Nonnull
+  Timestamp getReadTime();
+
+  @Nullable
+  Long getCount();
+
+  @Override
+  boolean equals(Object obj);
+
+  @Override
+  int hashCode();
+
+}

google-cloud-firestore/src/main/java/com/google/cloud/firestore/Query.java

@@ -1761,6 +1761,11 @@ private boolean isRetryableError(Throwable throwable) {
     return false;
   }
 
+  @Nonnull
+  public AggregateQuery count() {
+    throw new RuntimeException("not implemented");
+  }
+
   /**
    * Returns true if this Query is equal to the provided object.
    *

google-cloud-firestore/src/main/java/com/google/cloud/firestore/Transaction.java

@@ -190,4 +190,9 @@ public ApiFuture<QuerySnapshot> get(@Nonnull Query query) {
 
     return query.get(transactionId);
   }
+
+  @Nonnull
+  public ApiFuture<AggregateQuerySnapshot> get(@Nonnull AggregateQuery query) {
+    throw new RuntimeException("not implemented");
+  }
 }