Where should I put "prerequisite logic"?

rubyonrails-talk
1

Hi there,

I have this model called InventoryItem. Every time an InventoryItem is created (through the CharactersController and the create_item action) I need to update others tables and make lookups in other tables, to check if the Character has the prerequisites to actually create the InventoryItem.

My problem is that I cannot seem to find a good place to put this logic. I've tried to put it in a InventoryItem#validate_on_create. This is a hassle, because the InventoryItem has no direct association to all the things it need to check/update. Also, isn't it against the guide lines that validations actually updates/changes stuff as it is required here?

I've also tried placing most of the logic in the create_item action itself, however this also results in rather ugly code I think (see attached). This also has the drawback that InventoryItem validation errors and "prerequisite errors" are shown in different ways in the views, because they are stored in @inventory_item.errors and flash[:error] respectively.

There must be a better way? Where do you guys put logic like this? Any ideas/suggestions are very welcome.

Thanks in advance.

- Rasmus

Attachments: http://www.ruby-forum.com/attachment/2949/test.txt

2

Hi there,

I have this model called InventoryItem. Every time an InventoryItem is created (through the CharactersController and the create_item action) I need to update others tables and make lookups in other tables, to check if the Character has the prerequisites to actually create the InventoryItem.

I think validate_on_create is where you want to ensure that it's ok to create the InventoryItem.

Then use before_create to actually do the work of updating the related models. It's only called if all the validations pass.

My problem is that I cannot seem to find a good place to put this logic. I've tried to put it in a InventoryItem#validate_on_create. This is a hassle, because the InventoryItem has no direct association to all the things it need to check/update.

Why not? Sounds like an InventoryItem is associated to a Character, and so you should have access to all of Character's related tables as well. Maybe I'm missing something about the way you've setup your models?

Jeff

purpleworkshops.com

3

I guess you're right - maybe I should give it another go using validate_on_create and before_create

Jeff Cohen wrote:

Why not? Sounds like an InventoryItem is associated to a Character, and so you should have access to all of Character's related tables as well. Maybe I'm missing something about the way you've setup your models?

Well, it's like this: - Character has many InventoryItems - InventoryItems belongs to Item (an "item type" you could say) - Recipe belongs to Item

So when a new InventoryItem is created it has no "direct association" to a certain recipe - because recipe belongs to one Item (not InventoryItem). More than one recipe can belongs to the same Item.

This is why it is hard to do the validations inside InventoryItem. However, enlightened by your reply, I've made the following solution:

[code] class InventoryItem < ActiveRecord::Base   belongs_to :item   belongs_to :character   attr_accessor :recipe

  def recipe=(recipe)     self.item_id = recipe.product_item_id   end

  def self.new_from_recipe(recipe)     new :recipe => recipe   end

  def after_create     # something   end

  def validate_on_create     # something   end end [/code]

Do you see a better/simpler solution?