From 00b26532f05283d2b160308522d1bd2146d6ac18 Mon Sep 17 00:00:00 2001
From: Mauro George <maurogot@gmail.com>
Date: Mon, 8 Dec 2014 20:22:36 -0200
Subject: Add a hidden_field on the file_field

This will avoid a error be raised when the only input on the form is the
`file_field`.
---
 actionview/CHANGELOG.md                            |  6 ++++++
 actionview/lib/action_view/helpers/form_helper.rb  | 17 +++++++++++++++
 .../lib/action_view/helpers/tags/file_field.rb     | 13 +++++++++++
 actionview/test/template/form_helper_test.rb       | 25 +++++++++++++++++-----
 4 files changed, 56 insertions(+), 5 deletions(-)

(limited to 'actionview')

diff --git a/actionview/CHANGELOG.md b/actionview/CHANGELOG.md
index d71f29d7b0..4fa468dd91 100644
--- a/actionview/CHANGELOG.md
+++ b/actionview/CHANGELOG.md
@@ -3,4 +3,10 @@
 
     *Angelo Capilleri*
 
+*   Add a `hidden_field` on the `file_field` to avoid raise a error when the only
+    input on the form is the `file_field`.
+
+    *Mauro George*
+
+
 Please check [4-2-stable](https://github.com/rails/rails/blob/4-2-stable/actionview/CHANGELOG.md) for previous changes.
diff --git a/actionview/lib/action_view/helpers/form_helper.rb b/actionview/lib/action_view/helpers/form_helper.rb
index c4371dc705..e3a8f998a8 100644
--- a/actionview/lib/action_view/helpers/form_helper.rb
+++ b/actionview/lib/action_view/helpers/form_helper.rb
@@ -854,6 +854,23 @@ module ActionView
       #
       #   file_field(:attachment, :file, class: 'file_input')
       #   # => <input type="file" id="attachment_file" name="attachment[file]" class="file_input" />
+      #
+      # ==== Gotcha
+      #
+      # The HTML specification says when nothing is select on a file field web browsers do not send any value to server.
+      # Unfortunately this introduces a gotcha:
+      # if an +User+ model has a +avatar+ field, and in the form none file is selected no +avatar+ parameter is sent. So,
+      # any mass-assignment idiom like
+      #
+      #   @user.update(params[:user])
+      #
+      # wouldn't update avatar.
+      #
+      # To prevent this the helper generates an auxiliary hidden field before
+      # every file field. The hidden field has the same name as file field and blank value.
+      #
+      # In case if you don't want the helper to generate this hidden field you can specify
+      # <tt>include_hidden: false</tt> option.
       def file_field(object_name, method, options = {})
         Tags::FileField.new(object_name, method, self, options).render
       end
diff --git a/actionview/lib/action_view/helpers/tags/file_field.rb b/actionview/lib/action_view/helpers/tags/file_field.rb
index 476b820d84..02585fa0ae 100644
--- a/actionview/lib/action_view/helpers/tags/file_field.rb
+++ b/actionview/lib/action_view/helpers/tags/file_field.rb
@@ -2,6 +2,19 @@ module ActionView
   module Helpers
     module Tags # :nodoc:
       class FileField < TextField # :nodoc:
+
+        def render
+          options = @options.stringify_keys
+          if options.fetch("include_hidden", true)
+            add_default_name_and_id(options)
+            options[:type] = "file"
+            tag("input", :name => options["name"], :type => "hidden", :value => "") + tag("input", options)
+          else
+            options.delete("include_hidden")
+            @options = options
+            super
+          end
+        end
       end
     end
   end
diff --git a/actionview/test/template/form_helper_test.rb b/actionview/test/template/form_helper_test.rb
index 1459b9f02a..0b3d78ea9b 100644
--- a/actionview/test/template/form_helper_test.rb
+++ b/actionview/test/template/form_helper_test.rb
@@ -472,18 +472,33 @@ class FormHelperTest < ActionView::TestCase
     assert_dom_equal expected, text_field(object_name, "title")
   end
 
-  def test_file_field_has_no_size
+  def test_file_field_does_generate_a_hidden_field
+    expected = '<input name="user[avatar]" type="hidden" value="" /><input id="user_avatar" name="user[avatar]" type="file" />'
+    assert_dom_equal expected, file_field("user", "avatar")
+  end
+
+  def test_file_field_does_not_generate_a_hidden_field_if_included_hidden_option_is_false
+    expected = '<input id="user_avatar" name="user[avatar]" type="file" />'
+    assert_dom_equal expected, file_field("user", "avatar", :include_hidden => false)
+  end
+
+  def test_file_field_does_not_generate_a_hidden_field_if_included_hidden_option_is_false_with_key_as_string
     expected = '<input id="user_avatar" name="user[avatar]" type="file" />'
+    assert_dom_equal expected, file_field("user", "avatar", 'include_hidden' => false)
+  end
+
+  def test_file_field_has_no_size
+    expected = '<input name="user[avatar]" type="hidden" value="" /><input id="user_avatar" name="user[avatar]" type="file" />'
     assert_dom_equal expected, file_field("user", "avatar")
   end
 
   def test_file_field_with_multiple_behavior
-    expected = '<input id="import_file" multiple="multiple" name="import[file][]" type="file" />'
+    expected = '<input name="import[file][]" type="hidden" value="" /><input id="import_file" multiple="multiple" name="import[file][]" type="file" />'
     assert_dom_equal expected, file_field("import", "file", :multiple => true)
   end
 
   def test_file_field_with_multiple_behavior_and_explicit_name
-    expected = '<input id="import_file" multiple="multiple" name="custom" type="file" />'
+    expected = '<input name="custom" type="hidden" value="" /><input id="import_file" multiple="multiple" name="custom" type="file" />'
     assert_dom_equal expected, file_field("import", "file", :multiple => true, :name => "custom")
   end
 
@@ -1719,7 +1734,7 @@ class FormHelperTest < ActionView::TestCase
     end
 
     expected = whole_form("/posts/123", "create-post", "edit_post", method: "patch", multipart: true) do
-      "<input name='post[file]' type='file' id='post_file' />"
+      "<input name='post[file]' type='hidden' value='' /><input name='post[file]' type='file' id='post_file' />"
     end
 
     assert_dom_equal expected, output_buffer
@@ -1735,7 +1750,7 @@ class FormHelperTest < ActionView::TestCase
     end
 
     expected = whole_form("/posts/123", "edit_post_123", "edit_post", method: "patch", multipart: true) do
-      "<input name='post[comment][file]' type='file' id='post_comment_file' />"
+      "<input name='post[comment][file]' type='hidden' value='' /><input name='post[comment][file]' type='file' id='post_comment_file' />"
     end
 
     assert_dom_equal expected, output_buffer
-- 
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