feat(firestore): Add support for Query Partitions

google-cloud-firestore/acceptance/firestore/query_test.rb

@@ -284,4 +284,37 @@
     _(results.map(&:document_id)).must_equal ["doc1", "doc2"]
     _(results.map { |doc| doc[:foo] }).must_equal ["a", "b"]
   end
+
+  it "has to_json method and from_json class method" do
+    rand_query_col = firestore.col "#{root_path}/query/#{SecureRandom.hex(4)}"
+    rand_query_col.doc("doc1").create({foo: "a"})
+    rand_query_col.doc("doc2").create({foo: "b"})
+    rand_query_col.doc("doc3").create({foo: "c"})
+
+    original_query = rand_query_col.order(:foo).limit_to_last 2
+
+    json = original_query.to_json
+    _(json).must_be_instance_of String
+
+    query = Google::Cloud::Firestore::Query.from_json json, firestore
+    _(query).must_be_instance_of Google::Cloud::Firestore::Query
+
+    results_1 = []
+    query.get { |result| results_1 << result } # block directly to get, rpc
+    _(results_1.map(&:document_id)).must_equal ["doc2","doc3"]
+    _(results_1.map { |doc| doc[:foo] }).must_equal ["b","c"]
+
+    results_2 = []
+    query.get { |result| results_2 << result } # block directly to get, rpc
+    _(results_2.map(&:document_id)).must_equal ["doc2","doc3"]
+    _(results_2.map { |doc| doc[:foo] }).must_equal ["b","c"]
+
+    results_3 = query.get # enum_for :get
+    _(results_3.map(&:document_id)).must_equal ["doc2","doc3"] # rpc
+    _(results_3.map { |doc| doc[:foo] }).must_equal ["b","c"] # rpc
+
+    results_4 = query.get # enum_for :get
+    _(results_4.map(&:document_id)).must_equal ["doc2","doc3"] # rpc
+    _(results_4.map { |doc| doc[:foo] }).must_equal ["b","c"] # rpc
+  end
 end

google-cloud-firestore/lib/google/cloud/firestore/query.rb

@@ -17,6 +17,7 @@
 require "google/cloud/firestore/document_snapshot"
 require "google/cloud/firestore/query_listener"
 require "google/cloud/firestore/convert"
+require "json"
 
 module Google
   module Cloud
@@ -972,6 +973,67 @@ def listen &callback
         end
         alias on_snapshot listen
 
+        ##
+        # Serializes the instance to a JSON text string. See also {Query.from_json}.
+        #
+        # @return [String] A JSON text string.
+        #
+        # @example
+        #   require "google/cloud/firestore"
+        #
+        #   firestore = Google::Cloud::Firestore.new
+        #   query = firestore.col(:cities).select(:population)
+        #
+        #   json = query.to_json
+        #
+        #   new_query = Google::Cloud::Firestore::Query.from_json json, firestore
+        #
+        #   new_query.get do |city|
+        #     puts "#{city.document_id} has #{city[:population]} residents."
+        #   end
+        #
+        def to_json options = nil
+          query_json = Google::Cloud::Firestore::V1::StructuredQuery.encode_json query
+          {
+            "query" => JSON.parse(query_json),
+            "parent_path" => parent_path,
+            "limit_type" => limit_type
+          }.to_json options
+        end
+
+        ##
+        # Deserializes a JSON text string serialized from this class and returns it as a new instance. See also
+        # {#to_json}.
+        #
+        # @param [String] json A JSON text string serialized using {#to_json}.
+        # @param [Google::Cloud::Firestore::Client] client A connected client instance.
+        #
+        # @return [Query] A new query equal to the original query used to create the JSON text string.
+        #
+        # @example
+        #   require "google/cloud/firestore"
+        #
+        #   firestore = Google::Cloud::Firestore.new
+        #   query = firestore.col(:cities).select(:population)
+        #
+        #   json = query.to_json
+        #
+        #   new_query = Google::Cloud::Firestore::Query.from_json json, firestore
+        #
+        #   new_query.get do |city|
+        #     puts "#{city.document_id} has #{city[:population]} residents."
+        #   end
+        #
+        def self.from_json json, client
+          raise ArgumentError, "client is required" unless client
+
+          json = JSON.parse json
+          query_json = json["query"]
+          raise ArgumentError, "Field 'query' is required" unless query_json
+          query = Google::Cloud::Firestore::V1::StructuredQuery.decode_json query_json.to_json
+          start query, json["parent_path"], client, limit_type: json["limit_type"]&.to_sym
+        end
+
         ##
         # @private Start a new Query.
         def self.start query, parent_path, client, limit_type: nil

google-cloud-firestore/lib/google/cloud/firestore/query_partition.rb

@@ -63,7 +63,7 @@ def initialize query, start_at, end_before
         end
 
         ##
-        # Creates a new query that only returns the documents for this partition, using the cursor valuess from
+        # Creates a new query that only returns the documents for this partition, using the cursor values from
         # {#start_at} and {#end_before}.
         #
         # @return [Query] The query for the partition.

google-cloud-firestore/test/google/cloud/firestore/query/get_test.rb

@@ -253,6 +253,43 @@
     assert_results_enum results_enum
   end
 
+  it "gets a complex query after serialization and deserialization" do
+    expected_query = Google::Cloud::Firestore::V1::StructuredQuery.new(
+      select: Google::Cloud::Firestore::V1::StructuredQuery::Projection.new(
+        fields: [Google::Cloud::Firestore::V1::StructuredQuery::FieldReference.new(field_path: "name")]),
+      from: [Google::Cloud::Firestore::V1::StructuredQuery::CollectionSelector.new(collection_id: "users", all_descendants: false)],
+      offset: 3,
+      limit: Google::Protobuf::Int32Value.new(value: 42),
+      order_by: [
+        Google::Cloud::Firestore::V1::StructuredQuery::Order.new(
+          field: Google::Cloud::Firestore::V1::StructuredQuery::FieldReference.new(field_path: "name"),
+          direction: :ASCENDING),
+        Google::Cloud::Firestore::V1::StructuredQuery::Order.new(
+          field: Google::Cloud::Firestore::V1::StructuredQuery::FieldReference.new(field_path: "__name__"),
+          direction: :DESCENDING)],
+      start_at: Google::Cloud::Firestore::V1::Cursor.new(values: [Google::Cloud::Firestore::Convert.raw_to_value("foo")], before: false),
+      end_at: Google::Cloud::Firestore::V1::Cursor.new(values: [Google::Cloud::Firestore::Convert.raw_to_value("bar")], before: true)
+    )
+    firestore_mock.expect :run_query, query_results_enum, run_query_args(expected_query)
+
+    original_query = firestore.col(:users).select(:name).offset(3).limit(42).order(:name).order(firestore.document_id, :desc).start_after(:foo).end_before(:bar)
+
+    json = original_query.to_json
+    _(json).must_be_instance_of String
+
+    deserialized_query = Google::Cloud::Firestore::Query.from_json json, firestore
+    _(deserialized_query).must_be_instance_of Google::Cloud::Firestore::Query
+
+    _(deserialized_query.query).must_equal expected_query # Private field
+    _(deserialized_query.parent_path).must_equal original_query.parent_path # Private field
+    _(deserialized_query.limit_type).must_equal original_query.limit_type # Private field
+    _(deserialized_query.client).must_equal original_query.client # Private field
+
+    results_enum = deserialized_query.get
+
+    assert_results_enum results_enum
+  end
+
   def assert_results_enum enum
     _(enum).must_be_kind_of Enumerator