Should I use iterations to display sub categories?

rubyonrails-talk
1

Hello,

I have a categories table that has an id and a category_id so that I can have a :belongs_to on itself.

On the left of my website I would like to display the main categories, then their sub categories below them.

I have read in the book I have that iterations may be a possibility.

I thought that perhaps there are other ways to do this such has having in my controller have two instance variables, one would have categories where category_id is null to display top categories, then the other variable would would have categories where category_id = a certain id.

Of course I just thought that the above mentioned might not work because what about if I added a top category, then I would have to hard code something each time - not desirable.

So what are your suggestions after readin my babble?

2

Joel Slowik wrote:

Hello,

I have a categories table that has an id and a category_id so that I can have a :belongs_to on itself.

On the left of my website I would like to display the main categories, then their sub categories below them.

I have read in the book I have that iterations may be a possibility.

so far, so good. that's the best way to do it

I thought that perhaps there are other ways to do this such has having in my controller have two instance variables, one would have categories where category_id is null to display top categories, then the other variable would would have categories where category_id = a certain id.

you would need more instance vars. one for each sub-category. since most likely you don't know in advance how many that would be...

Of course I just thought that the above mentioned might not work because what about if I added a top category, then I would have to hard code something each time - not desirable.

So what are your suggestions after readin my babble?

you first load all cats with category_id 0, then iterate over children and so on. if necessary, in a recursive function but it's more likely, that you'll know the deepness of nested cats, than their amount. still easier, than making guesses about the number of categories and needed variables

3

You might want to look at acts_as_tree (now a plugin) -- it does what you're asking.

With your current design you might consider this:

class Category < ARec:Base

has_many :subcategories, :class_name=>'Category', :foreign_key=>'category_id'   ... end

You'll gain some db efficiency since you can do your initial fetch as:

  @categories = Category.find(:all, :conditions=>{:category_id=>nil}, :include=>:subcategories)

That will fetch all the 'main' categories and their immediate subcategories.