From 69142aa4ddf9a833aea483ea4c8d0844c5b9ae08 Mon Sep 17 00:00:00 2001
From: Mark Thomson <nzl216@gmail.com>
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(-)
(limited to 'actionpack')
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 %><br />
- # <%= f.label :author, 'Author' %>:
- # <%= f.text_field :author %><br />
- # <%= 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 %><br />
@@ -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
+ # <tt>:person</tt> 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 <tt><input></tt> tag whose +name+ attribute is
+ # <tt>person[first_name]</tt>. This means that when the form is submitted,
+ # the value entered by the user will be available in the controller as
+ # <tt>params[:person][:first_name]</tt>.
#
- # The rightmost argument to +form_for+ is an
- # optional hash of options:
+ # If <tt>:person</tt> also happens to be the name of an instance variable
+ # <tt>@person</tt>, 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
+ # <tt>@person</tt>.
#
- # * <tt>:url</tt> - 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 -
+ #
+ # * <tt>:url</tt> - 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
+ # <tt>:url</tt> 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).
# * <tt>:namespace</tt> - 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 <tt>@post</tt>
+ # 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. <tt>params[:post]</tt>
+ # if the object's class is +Post+. However, this can be overwritten using
+ # the <tt>:as</tt> 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 <tt>@post</tt> is an existing record you want to edit
+ # would result in <tt>params[:client]</tt>.
+ #
+ # 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 <tt>:url</tt> 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 <tt>config/routes.rb</tt>. 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
#
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