fields

Scopes input fields with either an explicit scope or model. Like form_with does with :scope or :model, except it doesn’t output the form tags.

# Using a scope prefixes the input field names:
<%= fields :comment do |fields| %>
  <%= fields.text_field :body %>
<% end %>
# => <input type="text" name="comment[body]">

# Using a model infers the scope and assigns field values:
<%= fields model: Comment.new(body: "full bodied") do |fields| %>
  <%= fields.text_field :body %>
<% end %>
# => <input type="text" name="comment[body]" value="full bodied">

# Using +fields+ with +form_with+:
<%= form_with model: @post do |form| %>
  <%= form.text_field :title %>

  <%= form.fields :comment do |fields| %>
    <%= fields.text_field :body %>
  <% end %>
<% end %>

Much like form_with a FormBuilder instance associated with the scope or model is yielded, so any generated field names are prefixed with either the passed scope or the scope inferred from the :model.

Mixing with other form helpers

While form_with uses a FormBuilder object it’s possible to mix and match the stand-alone FormHelper methods and methods from FormTagHelper:

<%= fields model: @comment do |fields| %>
  <%= fields.text_field :body %>

  <%= text_area :commenter, :biography %>
  <%= check_box_tag "comment[all_caps]", "1", @comment.commenter.hulk_mode? %>
<% end %>

Same goes for the methods in FormOptionsHelper and DateHelper designed to work with an object as a base, like FormOptionsHelper#collection_select and DateHelper#datetime_select.