Rails model foreign key not working when specifying explicitly

Question

I have a User model and a Message model. My message table has the columns created_for, and created_by and these are both foreign keys to the User table.

I'm currently getting this error message:

undefined methodcreated_for_id' for #`

How can I get this to work without having to change my columns to created_for_id and created_by_id?

class User < ActiveRecord::Base

    has_one :message
end

class Message < ActiveRecord::Base

    #belongs_to :user
    belongs_to :created_by, :class_name => "User" # Basically tell rails that created_by is a FK to the users table
    belongs_to :created_for, :class_name => "User"  # Basically tell rails that created_for is a FK to the users table

    attr_accessible :created_by, :created_for, :message

end

Dan McClain · Accepted Answer · 2014-03-21 01:08:41Z

2

You can specify the foreign key for the belongs_to via:

belongs_to :created_for, class_name: 'User', foreign_key: :created_for

I suspect you are going to run into an issue having the relation name and foreign key attribute sharing a name. Here is the belongs_to documentation, scroll down to the "Options"

answered Mar 21, 2014 at 1:08

Dan McClain

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5 Comments

Catfish Over a year ago

I added the foreign_key and i get this error: User(#70281925609240) expected, got String(#70281918088560). The line that throws the error is: @message = Message.new(params[:message]) and here's the params

{"utf8"=>"✓", "authenticity_token"=>"EYvFRZkOlK0rB5Dvflfa8iN47rZUorPle3usdaSRobk=", "message"=>{"created_for"=>"1", "message"=>"asdf"}, "button"=>"", "action"=>"create", "controller"=>"messages"}

Dan McClain Over a year ago

It has to be because the relation and the foreign key have the same name. I would change the name of one of them, as it's only going to cause problems, maybe call the relation for instead of created_for

Catfish Over a year ago

So if changed the column names to for and by, what would the foreign_key need to be? I guess i don't understand how changing for and by would make anything different.

Dan McClain Over a year ago

If the column was for, your relation would be defined like this belongs_to :created_for, class_name: 'User', foreign_key: 'for' when you had both the relation and the column sharing a name, when you set the foreign key on the model, it was doing a check to make sure it was the type specified in the belongs_to

Catfish Over a year ago

I just changed belongs_to :for. I used to think that a belongs_to had to be the label of your column.

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