Apply symbol-string key conversion to BSON::Document#dig too.

lib/bson/document.rb

@@ -172,6 +172,26 @@ def merge!(other)
 
     alias :update :merge!
 
+    if instance_methods.include?(:dig)
+      # Retrieves the value object corresponding to the each key objects repeatedly.
+      # Will normalize symbol keys into strings.
+      #
+      # @example Get value from nested sub-documents, handling missing levels.
+      #   document # => { :key1 => { "key2" => "value"}}
+      #   document.dig(:key1, :key2) # => "value"
+      #   document.dig("key1", "key2") # => "value"
+      #   document.dig("foo", "key2") # => nil
+      #
+      # @param [ Array<String, Symbol> ] *keys Keys, which constitute a "path" to the nested value.
+      #
+      # @return [ Object, NilClass ] The requested value or nil.
+      #
+      # @since 3.0.0
+      def dig(*keys)
+        super(*keys.map{|key| convert_key(key)})
+      end
+    end
+
     private
 
     def convert_key(key)

spec/bson/document_spec.rb

@@ -96,6 +96,28 @@
     end
   end
 
+  if described_class.instance_methods.include?(:dig)
+    describe "#dig" do
+      let(:document) do
+        described_class.new("key1" => { :key2 => "value" })
+      end
+
+      context "when provided string keys" do
+
+        it "returns the value" do
+          expect(document.dig("key1", "key2")).to eq("value")
+        end
+      end
+
+      context "when provided symbol keys" do
+
+        it "returns the value" do
+          expect(document.dig(:key1, :key2)).to eq("value")
+        end
+      end
+    end
+  end
+
   describe "#delete" do
 
     shared_examples_for "a document with deletable pairs" do
@@ -766,7 +788,7 @@
         "#{35.to_bson}"+
         "#{BSON::Document::BSON_TYPE}0#{BSON::NULL_BYTE}#{12.to_bson}#{BSON::Int32::BSON_TYPE}a#{BSON::NULL_BYTE}#{1.to_bson}#{BSON::NULL_BYTE}" +
         "#{BSON::Document::BSON_TYPE}1#{BSON::NULL_BYTE}#{12.to_bson}#{BSON::Int32::BSON_TYPE}b#{BSON::NULL_BYTE}#{2.to_bson}#{BSON::NULL_BYTE}" +
-        "#{BSON::NULL_BYTE}" + 
+        "#{BSON::NULL_BYTE}" +
         "#{BSON::NULL_BYTE}"
       end