Using Rails, how can I set my primary key to not be an integer-typed column?

user_219 0
Viewed 85010

I'm using Rails migrations to manage a database schema, and I'm creating a simple table where I'd like to use a non-integer value as the primary key (in particular, a string). To abstract away from my problem, let's say there's a table employees where employees are identified by an alphanumeric string, e.g. "134SNW".

I've tried creating the table in a migration like this:

create_table :employees, {:primary_key => :emp_id} do |t|
    t.string :emp_id
    t.string :first_name
    t.string :last_name
end

What this gives me is what seems like it completely ignored the line t.string :emp_id and went ahead and made it an integer column. Is there some other way to have rails generate the PRIMARY_KEY constraint (I'm using PostgreSQL) for me, without having to write the SQL in an execute call?

NOTE: I know it's not best to use string columns as primary keys, so please no answers just saying to add an integer primary key. I may add one anyway, but this question is still valid.

primary-key migration ruby-on-rails database
14 Answers

It looks like it is possible to do using this approach:

create_table :widgets, :id => false do |t|
  t.string :widget_id, :limit => 20, :primary => true

  # other column definitions
end

class Widget < ActiveRecord::Base
  set_primary_key "widget_id"
end

That will make the column widget_id the primary key for the Widget class, then it is up to you to populate the field when objects are created. You should be able to do so using the before create callback.

So something along the lines of

class Widget < ActiveRecord::Base
  set_primary_key "widget_id"

  before_create :init_widget_id

  private
  def init_widget_id
    self.widget_id = generate_widget_id
    # generate_widget_id represents whatever logic you are using to generate a unique id
  end
end
user_398190

you have to use the option :id => false

create_table :employees, :id => false, :primary_key => :emp_id do |t|
    t.string :emp_id
    t.string :first_name
    t.string :last_name
end
user_742640
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