如何在Rails创建表迁移中创建唯一索引？

Question

我正在使用Rails 5和PostgreSQL 9.5.如何在表格中创建唯一索引？我想从两列中创建唯一索引,这两列本身就是对其他表的引用.所以我试过了

class CreateUserNotificationsTable < ActiveRecord::Migration[5.0]
  def change
    create_table :user_notifications do |t|
      t.references :users, index: true, on_delete: :cascade
      t.references :crypto_currencies, index: true, on_delete: :cascade
      t.integer  "price",      null: false
      t.boolean "buy",      null: false
      t.index [:user_id, :crypto_currency_id], unique: true
    end
  end
end

但是我收到了错误

PG::UndefinedColumn: ERROR:  column "user_id" does not exist
: CREATE UNIQUE INDEX  "index_user_notifications_on_user_id_and_crypto_currency_id" ON "user_notifications"  ("user_id", "crypto_currency_id")
/Users/davea/.rvm/gems/ruby-2.4.0/gems/activerecord-5.0.4/lib/active_record/connection_adapters/postgresql/database_statements.rb:98:in `async_exec'
/Users/davea/.rvm/gems/ruby-2.4.0/gems/activerecord-5.0.4/lib/active_record/connection_adapters/postgresql/database_statements.rb:98:in `block in execute'
/Users/davea/.rvm/gems/ruby-2.4.0/gems/activerecord-5.0.4/lib/active_record/connection_adapters/abstract_adapter.rb:590:in `block in log'

在create table语句中创建唯一索引的正确方法是什么？

Answer 1

PG :: UndefinedColumn:错误:列"user_id"不存在

问题是t.references :users创建一个名为users_idnot 的列user_id,因此无法创建索引,t.index [:user_id, :crypto_currency_id], unique: true因为user_id未创建导致该错误的列.

解:

只需将其更改为t.references :user.同样t.references :crypto_currencies也是如此.

class CreateUserNotificationsTable < ActiveRecord::Migration[5.0]
  def change
    create_table :user_notifications do |t|
      t.references :user, index: true, on_delete: :cascade
      t.references :crypto_currency, index: true, on_delete: :cascade
      t.integer  "price",      null: false
      t.boolean "buy",      null: false
      t.index [:user_id, :crypto_currency_id], unique: true
    end
  end
end