CODEWITHSUNDEEP
ruby-on-railsvalidationmodel
eudaimonia
eudaimonia

Reputation: 1536

Rails add unique

This can be beginner thing, but I'm not sure how to deal with it. I want like to add unique constraint to column username in existing table psql

the migration create table :

class CreateRequests < ActiveRecord::Migration
  def change
    create_table :requests do |t|
      t.integer :user_id
      t.string :username
      t.string :address
      t.timestamps null: true
    end
    add_index :requests, :user_id
  end
end

So I added validation uniqueness in model

class Request < ModelBase
  belongs_to :user
  validates :user, presence: true
  validates :username, uniqueness: true
  ...

How can I add uniqueness to one column in the database via rails migration?

Upvotes: 4

Views: 9501

Answers (4)

lucas
lucas

Reputation: 1151

To get Ritesh Ranjan's solution using the rails migration generator, try:

rails g migration add_index_to_table_name column_name:uniq

At least in Rails 5.2, this will produce:

class AddIndexToTableName < ActiveRecord::Migration[5.2]
  def change
    add_column :table_name, :field_name, :string
    add_index :table_name, :field_name, unique: true
  end
end

You then just have to remove the add_column statement from the migration.

Upvotes: 2

Pietro Allievi
Pietro Allievi

Reputation: 436

if you want username to be unique, I suggest you to use validation in your app/models/user.rb:

class Request < ApplicationRecord
  validates :username, presence:true, uniqueness: {case_sensitive: false}

end

Upvotes: 1

Dima I. Belinski
Dima I. Belinski

Reputation: 381

def change
  remove_column :requests, :user_id
  change_column :requests, :username, :string, unique: true
  add_reference :requests, :user, index: true
end

Upvotes: 1

Ritesh Ranjan
Ritesh Ranjan

Reputation: 1012

At database level, the way you ensure uniqueness is via indexes. In a migration, create a new unique index for the column.

add_index :table_name, :column_name, :unique => true

Or:

rails g migration add_index_to_column_name :column_name, :unique => true

Please note that the creation will fail if you have duplicates in the current database. In that case, first go to the CLI and remove the duplicates, then run the migration.

Upvotes: 7

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