如何在 id 以外的 Rails 活动记录中创建唯一列

Question

class CreateUsers < ActiveRecord::Migration
   def up
     create_table :users do |t|
        t.string "email", :unique=>true

I was trying to add this unique option for making this email id unique in rails model but its not working so how can i make this email id unique ?

Answer 1

The unique option should be passed to an add_index call, not where you define your column.

Update your migration definition as follows:

class CreateUsers < ActiveRecord::Migration
   def up
     create_table :users do |t|
        t.string "email"
     end
     add_index :users, :email, unique: true
   end
   ...
end

And if you don't want to allow null then use t.string :email, null: false .

Answer 2

Update:
Right now I would advise against ignoring the index on the database level, you could check the answer below to find out how to add a database unique index.

The reason this is not a good idea is because of the possibility of a race condition, when more than one thread/process of the application would get a request to insert the same data in almost the same time, both threads would check if the email already exists in the database or not, and both would find out that the email does not exist at that moment, so both will pass the #validate check, then both would proceed to insert.
Then you would end up with having the same email in the database with no idea how that happened.

Having the validation is useful because you can react to the invalid record error in your controller.

Original Answer:
Why put restrictions on db level, I think putting a validation in the model level is more than enough, and at least whenever you need to change or remove restrictions you don't find your self needing to add a new migration

class User < ActiveRecord::Base
  validates :email, uniqueness: true
end