3 files changed, 40 insertions, 0 deletions
diff --git a/actionpack/CHANGELOG.md b/actionpack/CHANGELOG.md
index ddbe358bac..9a13e88ec9 100644
--- a/actionpack/CHANGELOG.md
+++ b/actionpack/CHANGELOG.md
@@ -1,3 +1,8 @@
+*   Add `ActionController::Parameters#dig` on Ruby 2.3 and greater, which
+    behaves the same as `Hash#dig`.
+
+    *Sean Griffin*
+
 *   Add request headers in the payload of the `start_processing.action_controller`
     and `process_action.action_controller` notifications.
 
diff --git a/actionpack/lib/action_controller/metal/strong_parameters.rb b/actionpack/lib/action_controller/metal/strong_parameters.rb
index a01110d474..6d59e32c68 100644
--- a/actionpack/lib/action_controller/metal/strong_parameters.rb
+++ b/actionpack/lib/action_controller/metal/strong_parameters.rb
@@ -430,6 +430,21 @@ module ActionController
       )
     end
 
+    if Hash.method_defined?(:dig)
+      # Extracts the nested parameter from the given +keys+ by calling +dig+
+      # at each step. Returns +nil+ if any intermediate step is +nil+.
+      #
+      # params = ActionController::Parameters.new(foo: { bar: { baz: 1 } })
+      # params.dig(:foo, :bar, :baz) # => 1
+      # params.dig(:foo, :zot, :xyz) # => nil
+      #
+      # params2 = ActionController::Parameters.new(foo: [10, 11, 12])
+      # params2.dig(:foo, 1)
+      def dig(*keys)
+        convert_value_to_parameters(@parameters.dig(*keys))
+      end
+    end
+
     # Returns a new <tt>ActionController::Parameters</tt> instance that
     # includes only the given +keys+. If the given +keys+
     # don't exist, returns an empty hash.
diff --git a/actionpack/test/controller/parameters/accessors_test.rb b/actionpack/test/controller/parameters/accessors_test.rb
index cea265f9ab..17c62dc3fe 100644
--- a/actionpack/test/controller/parameters/accessors_test.rb
+++ b/actionpack/test/controller/parameters/accessors_test.rb
@@ -194,4 +194,24 @@ class ParametersAccessorsTest < ActiveSupport::TestCase
 
     assert_match(/permitted: true/, @params.inspect)
   end
+
+  if Hash.method_defined?(:dig)
+    test "#dig delegates the dig method to its values" do
+      assert_equal "David", @params.dig(:person, :name, :first)
+      assert_equal "Chicago", @params.dig(:person, :addresses, 0, :city)
+    end
+
+    test "#dig converts hashes to parameters" do
+      assert_kind_of ActionController::Parameters, @params.dig(:person)
+      assert_kind_of ActionController::Parameters, @params.dig(:person, :addresses, 0)
+      assert @params.dig(:person, :addresses).all? do |value|
+        value.is_a?(ActionController::Parameters)
+      end
+    end
+  else
+    test "ActionController::Parameters does not respond to #dig on Ruby 2.2" do
+      assert_not ActionController::Parameters.method_defined?(:dig)
+      assert_not @params.respond_to?(:dig)
+    end
+  end
 end