feat: add datastore aggregation query APIs

protos/google/datastore/v1/aggregation_result.proto

@@ -0,0 +1,61 @@
+// 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.
+
+syntax = "proto3";
+
+package google.datastore.v1;
+
+import "google/datastore/v1/entity.proto";
+import "google/datastore/v1/query.proto";
+import "google/protobuf/timestamp.proto";
+
+option csharp_namespace = "Google.Cloud.Datastore.V1";
+option go_package = "google.golang.org/genproto/googleapis/datastore/v1;datastore";
+option java_multiple_files = true;
+option java_outer_classname = "AggregationResultProto";
+option java_package = "com.google.datastore.v1";
+option php_namespace = "Google\\Cloud\\Datastore\\V1";
+option ruby_package = "Google::Cloud::Datastore::V1";
+
+// The result of a single bucket from a Datastore aggregation query.
+//
+// The keys of `aggregate_properties` are the same for all results in an
+// aggregation query, unlike entity queries which can have different fields
+// present for each result.
+message AggregationResult {
+  // The result of the aggregation functions, ex: `COUNT(*) AS total_entities`.
+  //
+  // The key is the [alias][google.datastore.v1.AggregationQuery.Aggregation.alias]
+  // assigned to the aggregation function on input and the size of this map
+  // equals the number of aggregation functions in the query.
+  map<string, Value> aggregate_properties = 2;
+}
+
+// A batch of aggregation results produced by an aggregation query.
+message AggregationResultBatch {
+  // The aggregation results for this batch.
+  repeated AggregationResult aggregation_results = 1;
+
+  // The state of the query after the current batch.
+  // Only COUNT(*) aggregations are supported in the initial launch. Therefore,
+  // expected result type is limited to `NO_MORE_RESULTS`.
+  QueryResultBatch.MoreResultsType more_results = 2;
+
+  // Read timestamp this batch was returned from.
+  //
+  // In a single transaction, subsequent query result batches for the same query
+  // can have a greater timestamp. Each batch's read timestamp
+  // is valid for all preceding batches.
+  google.protobuf.Timestamp read_time = 3;
+}

protos/google/datastore/v1/datastore.proto

@@ -19,6 +19,7 @@ package google.datastore.v1;
 import "google/api/annotations.proto";
 import "google/api/client.proto";
 import "google/api/field_behavior.proto";
+import "google/datastore/v1/aggregation_result.proto";
 import "google/datastore/v1/entity.proto";
 import "google/datastore/v1/query.proto";
 import "google/protobuf/timestamp.proto";
@@ -61,6 +62,14 @@ service Datastore {
     };
   }
 
+  // Runs an aggregation query.
+  rpc RunAggregationQuery(RunAggregationQueryRequest) returns (RunAggregationQueryResponse) {
+    option (google.api.http) = {
+      post: "/v1/projects/{project_id}:runAggregationQuery"
+      body: "*"
+    };
+  }
+
   // Begins a new transaction.
   rpc BeginTransaction(BeginTransactionRequest) returns (BeginTransactionResponse) {
     option (google.api.http) = {
@@ -189,6 +198,45 @@ message RunQueryResponse {
   Query query = 2;
 }
 
+// The request for [Datastore.RunAggregationQuery][google.datastore.v1.Datastore.RunAggregationQuery].
+message RunAggregationQueryRequest {
+  // Required. The ID of the project against which to make the request.
+  string project_id = 8 [(google.api.field_behavior) = REQUIRED];
+
+  // The ID of the database against which to make the request.
+  //
+  // '(default)' is not allowed; please use empty string '' to refer the default
+  // database.
+  string database_id = 9;
+
+  // Entities are partitioned into subsets, identified by a partition ID.
+  // Queries are scoped to a single partition.
+  // This partition ID is normalized with the standard default context
+  // partition ID.
+  PartitionId partition_id = 2;
+
+  // The options for this query.
+  ReadOptions read_options = 1;
+
+  // The type of query.
+  oneof query_type {
+    // The query to run.
+    AggregationQuery aggregation_query = 3;
+
+    // The GQL query to run. This query must be an aggregation query.
+    GqlQuery gql_query = 7;
+  }
+}
+
+// The response for [Datastore.RunAggregationQuery][google.datastore.v1.Datastore.RunAggregationQuery].
+message RunAggregationQueryResponse {
+  // A batch of aggregation results. Always present.
+  AggregationResultBatch batch = 1;
+
+  // The parsed form of the `GqlQuery` from the request, if it was set.
+  AggregationQuery query = 2;
+}
+
 // The request for [Datastore.BeginTransaction][google.datastore.v1.Datastore.BeginTransaction].
 message BeginTransactionRequest {
   // Required. The ID of the project against which to make the request.

protos/google/datastore/v1/query.proto

@@ -118,6 +118,93 @@ message Query {
   google.protobuf.Int32Value limit = 12;
 }
 
+// Datastore query for running an aggregation over a [Query][google.datastore.v1.Query].
+message AggregationQuery {
+  // Defines a aggregation that produces a single result.
+  message Aggregation {
+    // Count of entities that match the query.
+    //
+    // The `COUNT(*)` aggregation function operates on the entire entity
+    // so it does not require a field reference.
+    message Count {
+      // Optional. Optional constraint on the maximum number of entities to count.
+      //
+      // This provides a way to set an upper bound on the number of entities
+      // to scan, limiting latency and cost.
+      //
+      // Unspecified is interpreted as no bound.
+      //
+      // If a zero value is provided, a count result of zero should always be
+      // expected.
+      //
+      // High-Level Example:
+      //
+      // ```
+      // AGGREGATE COUNT_UP_TO(1000) OVER ( SELECT * FROM k );
+      // ```
+      //
+      // Requires:
+      //
+      // * Must be non-negative when present.
+      google.protobuf.Int64Value up_to = 1 [(google.api.field_behavior) = OPTIONAL];
+    }
+
+    // The type of aggregation to perform, required.
+    oneof operator {
+      // Count aggregator.
+      Count count = 1;
+    }
+
+    // Optional. Optional name of the property to store the result of the aggregation.
+    //
+    // If not provided, Datastore will pick a default name following the format
+    // `property_<incremental_id++>`. For example:
+    //
+    // ```
+    // AGGREGATE
+    //   COUNT_UP_TO(1) AS count_up_to_1,
+    //   COUNT_UP_TO(2),
+    //   COUNT_UP_TO(3) AS count_up_to_3,
+    //   COUNT_UP_TO(4)
+    // OVER (
+    //   ...
+    // );
+    // ```
+    //
+    // becomes:
+    //
+    // ```
+    // AGGREGATE
+    //   COUNT_UP_TO(1) AS count_up_to_1,
+    //   COUNT_UP_TO(2) AS property_1,
+    //   COUNT_UP_TO(3) AS count_up_to_3,
+    //   COUNT_UP_TO(4) AS property_2
+    // OVER (
+    //   ...
+    // );
+    // ```
+    //
+    // Requires:
+    //
+    // * Must be unique across all aggregation aliases.
+    // * Conform to [entity property name][google.datastore.v1.Entity.properties] limitations.
+    string alias = 7 [(google.api.field_behavior) = OPTIONAL];
+  }
+
+  // The base query to aggregate over.
+  oneof query_type {
+    // Nested query for aggregation
+    Query nested_query = 1;
+  }
+
+  // Optional. Series of aggregations to apply over the results of the `nested_query`.
+  //
+  // Requires:
+  //
+  // * A minimum of one and maximum of five aggregations per query.
+  repeated Aggregation aggregations = 3 [(google.api.field_behavior) = OPTIONAL];
+}
+
 // A representation of a kind.
 message KindExpression {
   // The name of the kind.