How to find instance of an object in a collection within a collection in rails

I'm trying to write an if statement that will find an instance of an object in a collection within another collection...

House
has_many :occupants
Occupant
has_many :shirts
belongs_to :house
Shirt
belongs_to :occupant


So if I want check if any of the occupants of house own a white shirt, I want to do something like this:

<% if @house.occuptants.shirts.where(:color => 'white') %>


However when I do that I get an error:

undefined method `shirts' for #< Occupant::ActiveRecord_Associations_CollectionProxy

I believe because occupants is a collection in this case, but I'm not sure what the correct approach or syntax should be.

2 Answers
2

Something simpler and that will help you later for different use cases is to add more to the relationships:

class House
has_many :occupants
has_many :shirts, through: :occupants
end

class Occupant
has_many :shirts
belongs_to :house
scope :females, -> { where(...) } # This is homework for you: http://guides.rubyonrails.org/active_record_querying.html#scopes
end

class Shirt
belongs_to :occupant
end


If you have a House instance:then you can check for occupants with white shirts as below:

House

<% if @house.shirts.where(color: 'white').exists? %>


and to check for female occupants with white color shirts, do:

<% if @house.occupants.females.select { |o| o.shirts.where(color: 'white').exists? } %>


The condition of the if will always be true. where(color: 'white') cannot return a falsy value, it will always return an active record result wrapping 0 or more records. You need to use .exists? to return a boolean true/false.
– meagar♦
Jun 29 at 23:49

if

where(color: 'white')

.exists?

you are right, edited, thanks
– xploshioOn
Jun 29 at 23:51

This is helpful, but I've also got a similar scenario where I need to check just for females with white shirts, ie. I need to validate an attribute on occupant as well.... in this case would the decorator approach be necessary?
– phauwn
Jun 30 at 0:20

@phauwn i have updated the answer to include your further query. For next times, please try to include all your queries in the question itself. This answer was perfect in itself.
– Jagdeep Singh
Jun 30 at 7:08

Awesome @Jagdeep, don't worry, we are all here to help.
– xploshioOn
Jun 30 at 14:07

I would go for a presenter/decorator in this scenario.

Use draper to decorate the house object like:

# /app/decorators/house_decorator.rb
class HouseDecorator < Draper::Decorator
def count_occupants_with_white_shirts
object.occupants.joins(:shirts).where(shirts: { color: 'white' } ).count
end
end


Then in your view:

<% if @house.count_occupants_with_white_shirts > 0 %>


Hope that helps.

NOTE: If you don't want an additional dependency(Draper) you can also put that method inside you House model

House

This is not exactly decorating a model. It is more like adding a helper method to avoid calculations in the view. Should not go into the decorator. A good example of a decorator method is where you want to display a Time/Date object in pretty format.
– Jagdeep Singh
Jun 30 at 6:59

Time

Date

Also, you will have to call the method on @house.decorate.
– Jagdeep Singh
Jun 30 at 6:59

@house.decorate

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