通过rails中的迁移添加自动增量

Question

How to add an auto increment property to a column named user_number in my table users via Rails Migration.

I already have an id field which is its primary key and it is an autoincrement field. Im trying to create a new autoincrement field without deleting this id field..

Answer 1

class CreateSimpleModels < ActiveRecord::Migration
  def self.up
    create_table :simple_models do |t|
      t.string :name
      t.integer :user_number
      t.timestamps
    end
    execute "CREATE SEQUENCE simple_models_user_number_seq OWNED BY
simple_models.user_number INCREMENT BY 1 START WITH 1"
  end

  def self.down
    drop_table :simple_models
    execute "DELETE SEQUENCE simple_models_user_number_seq"
  end
end

Answer 2

You can directly modify your mysql table. Try this:

Alter table Tablename modify column ColumnName int(11) auto_increment;

You can take reference to Auto increment a non-primary key field in Ruby on Rails to execute it the rails way.

You can also come up with a pretty stupid hack, something like in your model, inside create method:

def self.create(user, user_number)
 user = User.new #update fields
 user.user_number += 1
 user.save
end

However I would still ask why don't you use the id itself as user_number ?