Adding a reference to a non-integer column in rails migration

Question

I have studied several questions on this topic today. I know that, I can use t.references in migration to add a reference. But, If a table has non-integer primary key, how do I add reference to that column?

I have a table with this definition

    create_table :sessions, id: false do |t|
      t.string  :session, primary_key: true, limit: 10  

      t.timestamps null: false
    end

How do I add a reference to the session column (the name doesn't matter here), which is a string from another table migration. I tested with t.references but that just add an integer column. I know that I can use add column. But how to do that without from create_table method directly?

Clarification for duplicate flag
This question is flagged as duplication of this question, but it is actually not. Because I am not asking about setting up table with non-default non-integer primary key, because I already set up that table. I am asking about referencing this type of table from another table.

Answer 1

Since rails version 4.2.7 You can specify type into the add_reference helper. Suppose you have table records and you want to have reference of sessions inside records. Then you can do the following :

add_reference :records, :sessions, type: :string, foreign_key: {to_table: :sessions, primary_key: :session}

Answer 2

Rather than using the references helper, you would need to use the string type, and add an index for faster lookups. If your other model is "Record":

rails generate migration AddSessionIdToRecords session:string:index

Which should generate a migration like so:

def change
  add_column :records, :session_id, :string
  add_index :records, :session_id
end

Since you're using unconventional naming, you'd need to specify the primary key in the model and the relation definition:

class Session < ActiveRecord::Base
  self.primary_key = "session"

  has_many :records, primary_key: "session"
end

class Record < ActiveRecord::Base
  belongs_to :session, primary_key: "session"
end