Custom association method - this can be done

Question

I have three models: Wager, Race, RaceCard and WagerType. I created a has_many association in Wagers and added a custom association method (in_wager). The purpose of this method is to filter out the correct races for each bet. (Some bets cover several races). I would like to be able to do something like: Wager.first.races.in_wager and return the corresponding races.

class Wager < ActiveRecord::Base belongs_to :wager_type belongs_to :race_card has_many :races, :through => :race_card do def in_wager where('races.race_nbr BETWEEN ? AND ?', a, b) end end end 

My custom method works fine if I hardcode the values ​​for a and b, however I need these values ​​to be dynamic. In particular, the value of b must be equal to the race_nbr attribute from the Wager model:

 b = wagers.race_nbr 

and the value of a should be equal to b minus the number of races for a certain type of bet (known as legs) plus 1:

 a = b - Legs + 1 

The leg value is in the WagerType model. Note that Wagers are owned by WagerType and WagerType has_many Wagers. Therefore, a can be expressed as:

 a = (b - (select wager_types.legs where wagers_types.id = wagers.wager_type_id) + 1) 

MY question is: is it really possible to do this with my in_wager association method. I’ve been staring at this couple for a couple of days and can’t figure out how to assign the correct values ​​a and b. Also, if you feel like I'm wrong, I would be glad to hear alternative approaches. Thank you for your help.

Note. I never mentioned the RaceCard or Races models. They have the following associations:

 class RaceCard < ActiveRecord::Base has_many :races end class Races < ActiveRecord::Base belongs_to :race_card has_many :wagers, :through => :race_card end 

Update: I read Design Templates in Ruby last night and stumbled upon Proc. I will see if I can use it in the Association method to calculate the values ​​for a and b.

Answer 1

you can use self.proxy_association.owner to get the parent object inside the association method. From there you can get the desired values.

If I understand your models correctly, then the code should look something like this.

 class Wager < ActiveRecord::Base belongs_to :wager_type belongs_to :race_card has_many :races, :through => :race_card do def in_wager owner = self.proxy_association.owner b = owner.race_nbr a = b - owner.wager_type.legs + 1 where('races.race_nbr BETWEEN ? AND ?', a, b) end end end 

I got this from the Rails Rails link to Association Extensions (The link to proxy_association is at the bottom of the section).

Answer 2

Do you need to use the has_many relation? maybe you could just create a method in the Wager class

 def races b = self.race_nbr a = b + self.race_card.legs Races.find_by_race_card_id(self.id).where('race_nbr BETWEEN ? AND ?', a, b) end 

I really don't understand your model, so the request is definitely erroneous, but you get the idea ...