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如何在Rails创建表迁移中创建唯一索引?

ruby-on-rails-5 rake migration postgresql ruby-on-rails

Dave · 技术社区 · 7 年前

我正在使用Rails 5和PostgreSQL 9.5。如何在表中创建唯一索引?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

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?

2 回复 | 直到 7 年前

Pavan Cesar 7 年前

PG::未定义列:错误:“user\u id”列不存在

问题是 t.references :users 创建一个名为 users_id user_id ,因此无法使用 t.index [:user_id, :crypto_currency_id], unique: true 作为列未创建导致该错误的。

解决方案:

把它改成 t.references :user . 同样适用于 t.references :crypto_currencies

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

itsnikolay 7 年前

create_table 方法,例如:

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
    end

    add_index :user_notifications, [:user_id, :crypto_currencies_id], unique: true
  end
end