RoR : Mongoid and form create hash - ruby-on-rails

Question

Simple question for Rails gurus. Why I do have to use the following statement to insert a new Mongoid document : params[:video][:description] in the following create method of my VideosController? Why I can't use the params[:description] from the POST form? If I use it, the value becomes nil.
def create
#video = Video.new(
:title => params[:video][:title],
:description => params[:video][:description]
)
if #video.save
render 'success'
else
render 'error'
end
end
Here is the Video.rb class :
class Video
include Mongoid::Document
field :title, type: String
field :description, type: String
validates_presence_of :title
validates_presence_of :description
acts_as_url :title
end
And finaly the form view :
<%= form_for #video do |f| %>
<%= f.label :title %>
<%= f.text_field :title %>
<p/>
<%= f.label :description %>
<%= f.text_field :description %>
<%= submit_tag("Enqueue video") %>
<% end %>
I don't quite get why the form input are video[description] and not just description as expected :
<label for="video_title">Title</label>
<input id="video_title" name="video[title]" type="text" />
<p/>
<label for="video_description">Description</label>
<input id="video_description" name="video[description]" type="text" />

Answer 1

When you are using form_for:
Creates a form that allows the user to create or update the attributes
of a specific model object.
In your case, Video model. To understand Rails convention:
<%= form_for #video do |f| %>
...
<%= f.text_field :description %>
...
Which results in an html tag whose name attribute is video[description]. This means that when the form is submitted, the value entered by the user will be available in the controller as params[:video][:description].
The params variable is an instace of ActiveSupport::HashWithIndifferentAccess, like a Hash with a small difference, according to documentation:
This class has dubious semantics and we only have it so that people
can write params[:key] instead of params[‘key’] and they get the same
value for both keys.
Your params is something like:
{"utf8"=>"✓",
"_method"=>"post",
"authenticity_token"=>"xxx",
"video"=>
{"description"=>"Video desc"}
}
Where "video" or :video is one of the keys of the Hash. So, params[:video] is equivalent to params.fetch("video") which value is {"description"=>"Video desc"}. As you can see the value is another Hash. Finally to get the value of the description you have to params[:video][:description] (The Rails way) or params.fetch("video").fetch("description"), which value is "Video desc".
fetch is a Ruby method of Hash: "Returns a value from the hash for the given key."
Taking this into account:
Video.new(params[:video]) = Video.new(:description => "Video desc") = Video.new(:description => params[:video][:description])
It's easier to use conventions, but for sure you can have params[:description] (just in case):
<%= form_for #video do |f| %>
...
<%= text_field_tag :description %>
...
Note that I'm using text_field_tag instead of f.text_field. In this case the html tag name will be description in the params Hash you will receive { "description" => 'Video desc" }...
Take a look to Rails API documentation to understand different helpers, etc. And also review your server's log.

Answer 2

If you want to use video[:description]. Create your form like this
<%= form_for #video do |f| %>
....
<p/>
<%= f.label :description %>
<%= f.text_field :description, :name => "description" %>
....
<% end %>
Rails form_for helper name the input elements such that it becomes easy to push them into model attributes in one go like this
#video = Video.new(params[:video])
so that you don't have to do it like the way you have done
#video = Video.new(
:title => params[:video][:title],
:description => params[:video][:description]
)