diff options
Diffstat (limited to 'actionview/lib/action_view/helpers/form_helper.rb')
| -rw-r--r-- | actionview/lib/action_view/helpers/form_helper.rb | 18 |
1 files changed, 18 insertions, 0 deletions
diff --git a/actionview/lib/action_view/helpers/form_helper.rb b/actionview/lib/action_view/helpers/form_helper.rb index c4371dc705..8d78ba13d5 100644 --- a/actionview/lib/action_view/helpers/form_helper.rb +++ b/actionview/lib/action_view/helpers/form_helper.rb @@ -854,6 +854,24 @@ 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 that when a file field is empty, web browsers + # do not send any value to the server. Unfortunately this introduces a + # gotcha: if a +User+ model has an +avatar+ field, and no file is selected, + # then the +avatar+ parameter is empty. Thus, any mass-assignment idiom like + # + # @user.update(params[:user]) + # + # wouldn't update the +avatar+ field. + # + # To prevent this, the helper generates an auxiliary hidden field before + # every file field. The hidden field has the same name as the file one and + # a blank value. + # + # In case you don't want the helper to generate this hidden field you can + # specify the <tt>include_hidden: false</tt> option. def file_field(object_name, method, options = {}) Tags::FileField.new(object_name, method, self, options).render end |