From 69142aa4ddf9a833aea483ea4c8d0844c5b9ae08 Mon Sep 17 00:00:00 2001 From: Mark Thomson Date: Sat, 10 Mar 2012 01:51:13 -0600 Subject: Revised explanation of form_for usage --- actionpack/lib/action_view/helpers/form_helper.rb | 137 +++++++++++++--------- 1 file changed, 84 insertions(+), 53 deletions(-) diff --git a/actionpack/lib/action_view/helpers/form_helper.rb b/actionpack/lib/action_view/helpers/form_helper.rb index 865914c1b7..41173de2e7 100644 --- a/actionpack/lib/action_view/helpers/form_helper.rb +++ b/actionpack/lib/action_view/helpers/form_helper.rb @@ -120,29 +120,14 @@ module ActionView object.respond_to?(:to_model) ? object.to_model : object end - # Creates a form and a scope around a specific model object that is used - # as a base for questioning about values for the fields. + # Creates a form that allows the user to create or update the attributes + # of a specific model object. # - # Rails provides succinct resource-oriented form generation with +form_for+ - # like this: - # - # <%= form_for @offer do |f| %> - # <%= f.label :version, 'Version' %>: - # <%= f.text_field :version %>
- # <%= f.label :author, 'Author' %>: - # <%= f.text_field :author %>
- # <%= f.submit %> - # <% end %> - # - # There, +form_for+ is able to generate the rest of RESTful form - # parameters based on introspection on the record, but to understand what - # it does we need to dig first into the alternative generic usage it is - # based upon. - # - # === Generic form_for - # - # The generic way to call +form_for+ yields a form builder around a - # model: + # The method can be used in several slightly different ways, depending on + # how much you wish to rely on Rails to infer automatically from the model + # how the form should be constructed. For a generic model object, a form + # can be created by passing +form_for+ a string or symbol representing + # the object we are concerned with: # # <%= form_for :person do |f| %> # First name: <%= f.text_field :first_name %>
@@ -152,24 +137,38 @@ module ActionView # <%= f.submit %> # <% end %> # - # There, the argument is a symbol or string with the name of the - # object the form is about. - # - # The form builder acts as a regular form helper that somehow carries the - # model. Thus, the idea is that + # The variable +f+ yielded to the block is a FormBuilder object that + # incorporates the knowledge about the model object represented by + # :person passed to +form_for+. Methods defined on the FormBuilder + # are used to generate fields bound to this model. Thus, for example, # # <%= f.text_field :first_name %> # - # gets expanded to + # will get expanded to # # <%= text_field :person, :first_name %> + # which results in an html tag whose +name+ attribute is + # person[first_name]. This means that when the form is submitted, + # the value entered by the user will be available in the controller as + # params[:person][:first_name]. # - # The rightmost argument to +form_for+ is an - # optional hash of options: + # If :person also happens to be the name of an instance variable + # @person, the default value of the field shown when the form is + # initially displayed (e.g. in the situation where you are editing an + # existing record) will be the value of the corresponding attribute of + # @person. # - # * :url - The URL the form is submitted to. It takes the same - # fields you pass to +url_for+ or +link_to+. In particular you may pass - # here a named route directly as well. Defaults to the current action. + # The rightmost argument to +form_for+ is an + # optional hash of options - + # + # * :url - The URL the form is to be submitted to. This may be + # represented in the same way as values passed to +url_for+ or +link_to+. + # So for example you may use a named route directly. When the model is + # represented by a string or symbol, as in the example above, if the + # :url option is not specified, by default the form will be + # sent back to the current url (We will describe below an alternative + # resource-oriented usage of +form_for+ in which the URL does not need + # to be specified explicitly). # * :namespace - A namespace for your form to ensure uniqueness of # id attributes on form elements. The namespace attribute will be prefixed # with underscore on the generated HTML id. @@ -179,7 +178,7 @@ module ActionView # possible to use both the stand-alone FormHelper methods and methods # from FormTagHelper. For example: # - # <%= form_for @person do |f| %> + # <%= form_for :person do |f| %> # First name: <%= f.text_field :first_name %> # Last name : <%= f.text_field :last_name %> # Biography : <%= text_area :person, :biography %> @@ -191,26 +190,65 @@ module ActionView # are designed to work with an object as base, like # FormOptionHelper#collection_select and DateHelper#datetime_select. # - # === Resource-oriented style + # === #form_for with a model object + # + # In the examples above, the object to be created or edited was + # represented by a symbol passed to +form_for+, and we noted that + # a string can also be used equivalently. It is also possible, however, + # to pass a model object itself to +form_for+. For example, if @post + # is an existing record you wish to edit, you can create the form using + # + # <%= form_for @post do |f| %> + # ... + # <% end %> + # + # This behaves in almost the same way as outlined previously, with a + # couple of small exceptions. First, the prefix used to name the input + # elements within the form (hence the key that denotes them in the +params+ + # hash) is actually derived from the object's _class_, e.g. params[:post] + # if the object's class is +Post+. However, this can be overwritten using + # the :as option, e.g. - # - # As we said above, in addition to manually configuring the +form_for+ - # call, you can rely on automated resource identification, which will use - # the conventions and named routes of that approach. This is the - # preferred way to use +form_for+ nowadays. + # <%= form_for(@person, :as => :client) do |f| %> + # ... + # <% end %> # - # For example, if @post is an existing record you want to edit + # would result in params[:client]. + # + # Secondly, the field values shown when the form is initially displayed + # are taken from the attributes of the object passed to +form_for+. + # Furthermore, this is true regardless of whether the object is an instance + # variable. So, for example, if we had a _local_ variable +post+ + # representing an existing record, + # + # <%= form_for post do |f| %> + # ... + # <% end %> + # + # would produce a form with fields whose initial state reflect the current + # values of the attributes of +post+. + # + # === Resource-oriented style + # + # In the examples just shown, although not indicated explicitly, we still + # need to use the :url option in order to specify where the + # form is going to be sent. However, further simplification is possible + # if the record passed to +form_for+ is a _resource_, i.e. it corresponds + # to a set of RESTful routes, e.g. defined using the +resources+ method + # in config/routes.rb. In this case Rails will simply infer the + # appropriate URL from the record itself. For example, # # <%= form_for @post do |f| %> # ... # <% end %> # - # is equivalent to something like: + # is then equivalent to something like: # # <%= form_for @post, :as => :post, :url => post_path(@post), :method => :put, :html => { :class => "edit_post", :id => "edit_post_45" } do |f| %> # ... # <% end %> # - # And for new records + # And for a new record # # <%= form_for(Post.new) do |f| %> # ... @@ -222,7 +260,7 @@ module ActionView # ... # <% end %> # - # You can also overwrite the individual conventions, like this: + # However you can still overwrite individual conventions, such as: # # <%= form_for(@post, :url => super_posts_path) do |f| %> # ... @@ -234,13 +272,6 @@ module ActionView # ... # <% end %> # - # If you have an object that needs to be represented as a different - # parameter, like a Person that acts as a Client: - # - # <%= form_for(@person, :as => :client) do |f| %> - # ... - # <% end %> - # # For namespaced routes, like +admin_post_url+: # # <%= form_for([:admin, @post]) do |f| %> @@ -263,9 +294,9 @@ module ActionView # # :method => (:get|:post|:patch|:put|:delete) # - # in the options hash. If the verb is not GET or POST, which are natively supported by HTML forms, the - # form will be set to POST and a hidden input called _method will carry the intended verb for the server - # to interpret. + # in the options hash. If the verb is not GET or POST, which are natively + # supported by HTML forms, the form will be set to POST and a hidden input + # called _method will carry the intended verb for the server to interpret. # # === Unobtrusive JavaScript # -- cgit v1.2.3