[英]Unique foreign key in rails migration
In migrations file, I'm adding foreign key using below syntax.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
But :unique => true
is not working.但是
:unique => true
不起作用。
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 | | |
+-------------+------------+---------------------+--------------+--------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
What is the right way to add a unique foreign key using migrations?使用迁移添加唯一外键的正确方法是什么?
I could've added uniqueness validations in the model itself.我可以在模型本身中添加唯一性验证。 But it won't be foolproof if I have multiple workers running.
但如果我有多个工人在运行,它就不会万无一失。 ( Reference )
( 参考)
In Rails 5 you can accomplish the same with the more elegant:在 Rails 5 中,您可以使用更优雅的方式完成相同的操作:
t.belongs_to :user, foreign_key: true, index: { unique: true }
This will generate a foreign key constraint as well as a unique index.这将生成一个外键约束以及一个唯一索引。 Don't forget to add
null: false
if this is a required association (sounds like it in the case of the original question).如果这是必需的关联,请不要忘记添加
null: false
(在原始问题的情况下听起来很像)。
Note that belongs_to
is just an alias for references
.请注意,
belongs_to
只是references
的别名。
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
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