Rake task foreign key assignment in a many to many relationship - ruby-on-rails

Question

I have two tables: Group and Keyword. They have a many-to-many relationship via another table called Assignments. I have a rake task where I generate random keywords, save the keyword to the Keyword's table and assign it to the current group's keywords. The code looks like this (I used a similar syntax to what I use in the console; however, I am not sure about it's correctness):
Group.populate 30 do |group|
Faker::Lorem.words(rand(3..7)).each do |key|
k = Keyword.create(name: key)
group.keywords << k
end
end
The << is returning this error: NoMethodError: undefined method<<'`.
If I ran the inner two lines in the console I get what I expect (note: I simplified the below models so you will see more keys in the log, but ignore that):
(0.1ms) begin transaction
SQL (2.0ms) INSERT INTO "keywords" ("name", "created_at", "updated_at") VALUES (?, ?, ?) [["name", "bla"], ["created_at", "2015-03-14 18:25:29.179793"], ["updated_at", "2015-03-14 18:25:29.179793"]]
(1.2ms) commit transaction
=> #<Keyword id: 1, name: "bla", created_at: "2015-03-14 18:25:29", updated_at: "2015-03-14 18:25:29">
(0.2ms) begin transaction
SQL (1.8ms) INSERT INTO "assignments" ("group_id", "keyword_id", "created_at", "updated_at") VALUES (?, ?, ?, ?) [["group_id", 1], ["keyword_id", 1], ["created_at", "2015-03-14 18:26:53.650257"], ["updated_at", "2015-03-14 18:26:53.650257"]]
(0.8ms) commit transaction
=> #<ActiveRecord::Associations::CollectionProxy [#<Keyword id: 1, name: "bla", created_at: "2015-03-14 18:25:29", updated_at: "2015-03-14 18:25:29">]>
The Group model looks like this:
class Group < ActiveRecord::Base
has_many :assignments, dependent: :destroy
has_many :keywords, through: :assignments, dependent: :destroy
end
The Keyword model looks like that:
class Keyword < ActiveRecord::Base
has_many :assignments
has_many :groups, through: :assignments
end
And the Assignment model looks like this:
class Assignment < ActiveRecord::Base
belongs_to :group
belongs_to :keyword
end
How can I modify this code to work as expected?

Answer 1

TRy this
class Group < ActiveRecord::Base
has_many :assignments, dependent: :destroy
has_many :active_assignments, dependent: :destroy, class_name: "Assignment"
has_many :keywords, through: :active_assignments, source: :keyword
class Keyword < ActiveRecord::Base
has_many :assignments, dependent: :destroy
has_many :groups, through: :assignments
end
class Assignment < ActiveRecord::Base
belongs_to :group
belongs_to :keyword
end
Group.populate 30 do |group|
Faker::Lorem.words(rand(3..7)).each do |key|
group.keywords << Keyword.create(name: key)
end
end

Answer 2

I found the problem in my program. Even though it was a stupid mistake from me, I will leave the question and the error reported in case anybody fall into the same issue in the future.
I had this error because I had a field in my Group table which is named keywords, which of course conflicted with the Keywords table (which has many-to-many relation to Groups). I had this field from before I decided to create the many-to-many relation, and I forgot to remove it. Then, of course when you type something like this command group.keywords << Keyword.create(name: key) you will get this weird error: NoMethodError: undefined method<<.
However, fixing this mistake will not make the rake task run. This is because Group.populate returns a Populator object. If you run this task you will get this error: NoMethodError: undefined method keywords for #<Populator::Record:0x007fa1ee78fba8>. To fix that issue I had to assign the foreign keys manually in the task like so:
Group.populate 30 do |group|
Faker::Lorem.words(rand(3..7)).each do |key|
k = Keyword.create(name: key)
a = Assignment.create(keyword_id: k.id, group_id: group.id)
end
end
which will run as expected.