rails迁移中的唯一外键

Question

在迁移文件中,我使用以下语法添加外键.

class CreatePreferences < ActiveRecord::Migration
  def change
    create_table :preferences do |t|
      t.integer :user_id, null: false
      t.timestamps null: false
    end
    add_foreign_key :preferences, :users, column: :user_id, dependent: :destroy, :unique => true
  end
end

但是:unique => true没有用.

mysql> show indexes from preferences;
+-------------+------------+---------------------+--------------+--------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table       | Non_unique | Key_name            | Seq_in_index | Column_name  | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+-------------+------------+---------------------+--------------+--------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| preferences |          0 | PRIMARY             |            1 | id           | A         |           0 |     NULL | NULL   |      | BTREE      |         |               |
| preferences |          1 | fk_rails_87f1c9c7bd |            1 | user_id      | A         |           0 |     NULL | NULL   |      | BTREE      |         |               |
+-------------+------------+---------------------+--------------+--------------+-----------+-------------+----------+--------+------+------------+---------+---------------+

使用迁移添加唯一外键的正确方法是什么？

我可以在模型中添加唯一性验证.但如果我有多个工人在跑,那就不会万无一失.(参考)

Answer 1

在Rails 5中,你可以用更优雅的方式完成同样的工作:

t.belongs_to :user, foreign_key: true, index: { unique: true }

这将生成外键约束以及唯一索引.null: false如果这是必需的关联,请不要忘记添加(在原始问题的情况下听起来像这样).

请注意,这belongs_to只是一个别名references.

Answer 2

class CreatePreferences < ActiveRecord::Migration
  def change
    create_table :preferences do |t|
      t.integer :user_id, null: false
      t.timestamps null: false
    end
    add_foreign_key :preferences, :users, column: :user_id, dependent: :destroy, :unique => true
    add_index :preferences, :user_id, unique: true
  end
end