Has many_through, how to show only unassociated fields for a category?

rubyonrails-talk
1

Hi everybody,

I'm using ruby 1.9.1, with rails 2.3.*. I have an application of products and categories, but I want each type of product to have specific attributes. So, basically, according to the chosen category, I want different fields to be shown for the user.

So, before actually making the association of the product with the attribute, I want to create an administration system where the administrators could actually select wich fields they want for each category, in an N:N association, usign has many through (categoryFields is the middle table). So, up to now, the structure is:

class Field < ActiveRecord::Base     has_many :categoryFields, :dependent => :destroy     has_many :categories, :through => :categoryFields end

class CategoryField < ActiveRecord::Base     belongs_to :field     belongs_to :category end

class Category < ActiveRecord::Base has_many :categoryFields, :dependent => :destroy has_many :fields, :through => :categoryFields end

And this works perfectly. so, now, in my Category Edit view, I want to show a list of ALL AVAILABLE FIELDS (i.e. only those not already associated to that specific category) at the right, and in the left, all the ASSOCIATED FIELDS for that category. Using a simple drag-and-drop, the user can drag fields from the right to insert them in category, or move them to the right to remove them from that specific category.

The problem is that I don't want that any field in the left column also appear in the right column (each field can only be used once in that specific category, since those attributes are unique). So, once you have associated a field to a category, it will not appear in the list of available fields (right list). I'm coming from PHP and this is my first rails application (I know, it's kinda complicated for a noob).

So, what should I do, to exclude those values?

The edit method in the category controller: @category = Category.find(params[:id]) @categories = Category.roots #the categories acts as nested set, so we have to fetch all available parent categories @fields = Field.all

Now, the view do the following:   <div class="category_fields span-12 last">   <% if !@category.fields.empty? # this loops through all teh ASSOCIATED fields and display their names%>     <% @category.fields.each do |field| %>       <%=field.name%>     <% end %>   <% end %>   </div>   <div class="fields_available">     <% if !@fields.empty? # this loops through ALL THE fields and display their names %>     <% @fields.each do |field| %>       <%=field.name%>     <% end %>   <% end %>   </div>

So, where should I place the "filter" so that only available fields will appear in the second div? Shoud I place it in the controller, as a condition somehow, and how? Or should I use some array-function to "pop out" the already associated fields from the @fields array? Wich is better from the point of view of performance, and how do I do each of them?

Thanks a lot in advice, for any help Samuel Brandão web@samuelbrandao.com.br

2

Fields.all gives you an array of all the fields in the database @category.fields gives you an array of all the fields for the given category (since you have the has_many :fields, :through => :categoryFields association)

How do you get the fields that are present in the first array but not in the second? Subtraction.

@fields_not_chosen_yet = Fields.all - @category.fields

Btw, you may want to exchange :categoryFields for :category_fields.

3

Hi Sharagoz, thank you for your reply. However, I had already tried array subtraction once, but with no success.

I tried for example:

associatedFields = @category.fields allFields = Field.all

available = allFields - associatedFields

however it did not work. When I try:

associatedFields.inspect

[#, #, #, #]

allFields.inspect

[#, #, #, #, #, #, #, #]

It seems to me that those resulting variables (allFields and associatedFields) are not of the specific class Array, or if they are, the subtraction is not working properly. I'm gonna do some more tests, to make sure i'm not screwing somewhere else.

thanks in advice for any help (at least I know i'm in the right direction :D)

Is there ANY way to make this subtraction/selection through SQL queries?

4

associatedFields = @category.fields allFields = Field.all

available = allFields - associatedFields

Field.all :conditions => ["id not in (?)", @category.fields.all.map(&:id)]

Field.where(["id not in (?)", @category.fields.all.map(&:id)]) if rails 3

Ivan Nastyukhin dieinzige@me.com