Encountered NoMethodError when binding two table data in Rails console

I have established an association between three models, where User can has_many Recipe, and Recipe belongs_to User. This is what the model sets:

model User

has_many :reviews
has_many :recipes, through: :reviews

model Recipe

has_many :reviews
has_many :users
belongs_to :user

model Review

  belongs_to :user
  belongs_to :recipe

Currently, User and Recipe each have a data. I want to assign Recipe to User, so I did the following in the Rails console:

u2 = User.find_by_id(2)
r1 = Recipe.find_by_id(1)
u2.recipes = r1

Then "NoMethodError (undefined method `each’ for #Recipe:0x0000560632fde3d0)" appears.

I can’t understand, has_many or has_one should generate recipes and recipes= methods, why doesn’t this work?

>Solution :

It doesn’t work since you’re attempting to assign a single record to a has_many assocation. The reason you’re getting undefined method 'each' is that the generated setter expects an array or a an assocation that can be iterated upon. For example:

user = User.find(2)
user.recipies = Recipe.where(id: 1)

But the idiomatically correct way to assign a single record to a has_many or has_and_belongs_to_many assocation is with the shovel method:

u2 = User.find_by_id(2)
r1 = Recipe.find_by_id(1)
u2.recipes << r1

With an indirect assiation Rails will implicitly create the rows in the join table.