The Active Record Helper makes it easier to create forms for records kept in instance variables. The most far-reaching is the form method that creates a complete form for all the basic content types of the record (not associations or aggregations, though). This is a great way of making the record quickly available for editing, but likely to prove lackluster for a complicated real-world form. In that case, it‘s better to use the input method and the specialized form methods in classes/ActionView/Helpers/FormHelper.html

Public Instance methods
error_message_on(object, method, *args)

Returns a string containing the error message attached to the method on the object if one exists. This error message is wrapped in a DIV tag, which can be extended to include a :prepend_text and/or :append_text (to properly explain the error), and a :css_class to style it accordingly. object should either be the name of an instance variable or the actual object. The method can be passed in either as a string or a symbol. As an example, let‘s say you have a model @post that has an error message on the title attribute:

  <%= error_message_on "post", "title" %>
  # => <div class="formError">can't be empty</div>

  <%= error_message_on @post, :title %>
  # => <div class="formError">can't be empty</div>

  <%= error_message_on "post", "title",
      :prepend_text => "Title simply ",
      :append_text => " (or it won't work).",
      :css_class => "inputError" %>
     # File actionpack/lib/action_view/helpers/active_record_helper.rb, line 109
109:       def error_message_on(object, method, *args)
110:         options = args.extract_options!
111:         unless args.empty?
112:           ActiveSupport::Deprecation.warn('error_message_on takes an option hash instead of separate ' +
113:             'prepend_text, append_text, and css_class arguments', caller)
115:           options[:prepend_text] = args[0] || ''
116:           options[:append_text] = args[1] || ''
117:           options[:css_class] = args[2] || 'formError'
118:         end
119:         options.reverse_merge!(:prepend_text => '', :append_text => '', :css_class => 'formError')
121:         if (obj = (object.respond_to?(:errors) ? object : instance_variable_get("@#{object}"))) &&
122:           (errors = obj.errors.on(method))
123:           content_tag("div",
124:             "#{options[:prepend_text]}#{ERB::Util.html_escape(errors.is_a?(Array) ? errors.first : errors)}#{options[:append_text]}".html_safe,
125:             :class => options[:css_class]
126:           )
127:         else
128:           ''
129:         end
130:       end

Returns a string with a DIV containing all of the error messages for the objects located as instance variables by the names given. If more than one object is specified, the errors for the objects are displayed in the order that the object names are provided.

This DIV can be tailored by the following options:

  • :header_tag - Used for the header of the error div (default: "h2").
  • :id - The id of the error div (default: "errorExplanation").
  • :class - The class of the error div (default: "errorExplanation").
  • :object - The object (or array of objects) for which to display errors, if you need to escape the instance variable convention.
  • :object_name - The object name to use in the header, or any text that you prefer. If :object_name is not set, the name of the first object will be used.
  • :header_message - The message in the header of the error div. Pass nil or an empty string to avoid the header message altogether. (Default: "X errors prohibited this object from being saved").
  • :message - The explanation message after the header message and before the error list. Pass nil or an empty string to avoid the explanation message altogether. (Default: "There were problems with the following fields:").

To specify the display for one object, you simply provide its name as a parameter. For example, for the @user model:

  error_messages_for 'user'

To specify more than one object, you simply list them; optionally, you can add an extra :object_name parameter, which will be the name used in the header message:

  error_messages_for 'user_common', 'user', :object_name => 'user'

If the objects cannot be located as instance variables, you can add an extra :object parameter which gives the actual object (or array of objects to use):

  error_messages_for 'user', :object => @question.user

NOTE: This is a pre-packaged presentation of the errors with embedded strings and a certain HTML structure. If what you need is significantly different from the default presentation, it makes plenty of sense to access the object.errors instance yourself and set it up. View the source of this method to see how easy it is.

     # File actionpack/lib/action_view/helpers/active_record_helper.rb, line 170
170:       def error_messages_for(*params)
171:         options = params.extract_options!.symbolize_keys
173:         if object = options.delete(:object)
174:           objects = Array.wrap(object)
175:         else
176:           objects = params.collect {|object_name| instance_variable_get("@#{object_name}") }.compact
177:         end
179:         count  = objects.inject(0) {|sum, object| sum + object.errors.count }
180:         unless
181:           html = {}
182:           [:id, :class].each do |key|
183:             if options.include?(key)
184:               value = options[key]
185:               html[key] = value unless value.blank?
186:             else
187:               html[key] = 'errorExplanation'
188:             end
189:           end
190:           options[:object_name] ||= params.first
192:           I18n.with_options :locale => options[:locale], :scope => [:activerecord, :errors, :template] do |locale|
193:             header_message = if options.include?(:header_message)
194:               options[:header_message]
195:             else
196:               object_name = options[:object_name].to_s
197:               object_name = I18n.t(object_name, :default => object_name.gsub('_', ' '), :scope => [:activerecord, :models], :count => 1)
198:               locale.t :header, :count => count, :model => object_name
199:             end
200:             message = options.include?(:message) ? options[:message] : locale.t(:body)
201:             error_messages = objects.sum {|object| {|msg| content_tag(:li, ERB::Util.html_escape(msg)) } }.join.html_safe
203:             contents = ''
204:             contents << content_tag(options[:header_tag] || :h2, header_message) unless header_message.blank?
205:             contents << content_tag(:p, message) unless message.blank?
206:             contents << content_tag(:ul, error_messages)
208:             content_tag(:div, contents.html_safe, html)
209:           end
210:         else
211:           ''
212:         end
213:       end
form(record_name, options = {}) {|contents if block_given?| ...}

Returns an entire form with all needed input tags for a specified Active Record object. For example, if @post has attributes named title of type VARCHAR and body of type TEXT then


would yield a form like the following (modulus formatting):

  <form action='/posts/create' method='post'>
      <label for="post_title">Title</label><br />
      <input id="post_title" name="post[title]" size="30" type="text" value="Hello World" />
      <label for="post_body">Body</label><br />
      <textarea cols="40" id="post_body" name="post[body]" rows="20"></textarea>
    <input name="commit" type="submit" value="Create" />

It‘s possible to specialize the form builder by using a different action name and by supplying another block renderer. For example, if @entry has an attribute message of type VARCHAR then

    :action => "sign",
    :input_block => { |record, column|
      "#{column.human_name}: #{input(record,}<br />"

would yield a form like the following (modulus formatting):

  <form action="/entries/sign" method="post">
    <input id="entry_message" name="entry[message]" size="30" type="text" /><br />
    <input name="commit" type="submit" value="Sign" />

It‘s also possible to add additional content to the form by giving it a block, such as:

  form("entry", :action => "sign") do |form|
    form << content_tag("b", "Department")
    form << collection_select("department", "id", @departments, "id", "name")

The following options are available:

  • :action - The action used when submitting the form (default: create if a new record, otherwise update).
  • :input_block - Specialize the output using a different block, see above.
  • :method - The method used when submitting the form (default: post).
  • :multipart - Whether to change the enctype of the form to "multipart/form-data", used when uploading a file (default: false).
  • :submit_value - The text of the submit button (default: "Create" if a new record, otherwise "Update").
    # File actionpack/lib/action_view/helpers/active_record_helper.rb, line 75
75:       def form(record_name, options = {})
76:         record = instance_variable_get("@#{record_name}")
78:         options = options.symbolize_keys
79:         options[:action] ||= record.new_record? ? "create" : "update"
80:         action = url_for(:action => options[:action], :id => record)
82:         submit_value = options[:submit_value] || options[:action].gsub(/[^\w]/, '').capitalize
84:         contents = form_tag({:action => action}, :method =>(options[:method] || 'post'), :enctype => options[:multipart] ? 'multipart/form-data': nil)
85:         contents.safe_concat hidden_field(record_name, :id) unless record.new_record?
86:         contents.safe_concat all_input_tags(record, record_name, options)
87:         yield contents if block_given?
88:         contents.safe_concat submit_tag(submit_value)
89:         contents.safe_concat '</form>'
90:       end
input(record_name, method, options = {})

Returns a default input tag for the type of object returned by the method. For example, if @post has an attribute title mapped to a VARCHAR column that holds "Hello World":

  input("post", "title")
  # => <input id="post_title" name="post[title]" size="30" type="text" value="Hello World" />
    # File actionpack/lib/action_view/helpers/active_record_helper.rb, line 21
21:       def input(record_name, method, options = {})
22:, method, self).to_tag(options)
23:       end