How to set an attribute to Array in Model?

Question

Can you teach me how to set an attribute to Array in Model?.

I have tried it but when I use array's method like push, each, I got the error undefined method `push' for nil:NilClass

My migrate look like this:

class CreateContacts < ActiveRecord::Migration
  def change
    create_table :contacts do |t|
      t.string :name
      t.string :email
      t.string :email_confirmation
      t.integer :city_ids, array: true
      t.text :description

      t.timestamps
    end
  end
end

I would like to set attribute city_ids to Array.

have you check this one reefpoints.dockyard.com/ruby/2012/09/18/… — Arihant Godha
– Arihant Godha, Commented Jan 16, 2014 at 4:14
Thank you, but It still not work for me, I can't use array method in attribute which set to be an array — Yuto Yasunaga
– Yuto Yasunaga, Commented Jan 16, 2014 at 8:35

Arihant Godha · Accepted Answer · 2014-01-16 04:17:06Z

3

One important thing to note when interacting with array (or other mutable values) on a model. ActiveRecord does not currently track "destructive", or in place changes. These include array pushing and poping, advance-ing DateTime objects. Example

 john = User.create(:first_name => 'John', :last_name => 'Doe',
  :nicknames => ['Jack', 'Johnny'])

john = User.first

john.nicknames += ['Jackie boy']
# or
john.nicknames = john.nicknames.push('Jackie boy')
# Any time an attribute is set via `=`, ActiveRecord tracks the change
john.save

Referrence - link

answered Jan 16, 2014 at 4:17

Arihant Godha

2,5192 gold badges28 silver badges53 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

user229044 · Accepted Answer · 2014-01-16 04:14:06Z

1

You need to set a default. Otherwise, the attribute is nil, until you give it a value:

  t.integer :city_ids, array: true, default: []

Or, you need to give it a value befor eyou attempt to use it:

c = City.find(...)

c.city_ids ||= []

c.city_ids.push(...)

answered Jan 16, 2014 at 4:14

user229044♦

241k41 gold badges347 silver badges350 bronze badges

1 Comment

Yuto Yasunaga Over a year ago

I use that array attribute for multiple check box, I have some checkbox and when it checked, array attribute will add value into. But I still can't use array method like "push, first, last" because NoMethodError

Collectives™ on Stack Overflow

How to set an attribute to Array in Model?

2 Answers 2

Comments

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related