Afsane Fadaei Afsane Fadaei - 27 days ago 10
Ruby Question

Assigne a value to an active record relation field

This is my first model :

class Sender < ApplicationRecord
has_many :letters
end


and this is the Second one:

class Letter < ApplicationRecord
belongs_to :sender
end


I find a letter like this in rails Consol :

@letter = Letter.where(id: 378)


the result is :

#<ActiveRecord::Relation [#<Letter id: 378, indicator: "95/2", classification: "aa", urgency: "aa", package_id: nil, registrar_id: 0, user_id: nil, subset_type: "official", created_at: "2016-11-10 06:02:14", updated_at: "2016-11-10 06:02:14", sender_id: nil>]>


as you can see the sender_id is nil.
The thing I want is to set a value to the sender_id like this :

@letter.sender_id = 12


but I got this error:

NoMethodError: undefined method `sender_id=' for #<Letter::ActiveRecord_Relation:0x00000004cc96c0>
Did you mean? send_later
from /var/lib/gems/2.3.0/gems/activerecord-5.0.0.1/lib/active_record/relation/delegation.rb:123:in `method_missing'
from /var/lib/gems/2.3.0/gems/activerecord-5.0.0.1/lib/active_record/relation/delegation.rb:93:in `method_missing'
from (irb):19
from /var/lib/gems/2.3.0/gems/railties-5.0.0.1/lib/rails/commands/console.rb:65:in `start'
from /var/lib/gems/2.3.0/gems/railties-5.0.0.1/lib/rails/commands/console_helper.rb:9:in `start'
from /var/lib/gems/2.3.0/gems/railties-5.0.0.1/lib/rails/commands/commands_tasks.rb:78:in `console'
from /var/lib/gems/2.3.0/gems/railties-5.0.0.1/lib/rails/commands/commands_tasks.rb:49:in `run_command!'
from /var/lib/gems/2.3.0/gems/railties-5.0.0.1/lib/rails/commands.rb:18:in `<top (required)>'
from bin/rails:4:in `require'
from bin/rails:4:in `<main>'


What's wrong?

Answer
Letter.where(id: 378)

returns a collection of records matching the query condition. And of course, you do not have a method sender_id= for an ActiveRecord::Relation object.

What you want instead is a single record, which can be get by either

@letter = Letter.where(id: 378).first

or

@letter = Letter.find(id: 378)

Now, having a single record, you can update it's sender_id attribute:

@letter.update(sender_id: 12)