Ruby-on-rails Rails：验证两列的唯一性（一起）
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Rails: validate uniqueness of two columns (together)
提问by Hymanson Cunningham
I have a Releasemodel with mediumand countrycolumns (among others). There should not be releasesthat share identical medium/countrycombinations.
我有一个Release带有medium和country列的模型（等等）。不应该releases有相同的medium/country组合。
How would I write this as a rails validation?
我将如何将其编写为 Rails 验证？
回答by tompave
You can use a uniquenessvalidation with the scopeoption.
您可以使用该选项的唯一性验证scope。
Also, you should add a unique index to the DB to prevent new records from passing the validations when checked at the same time before being written:
此外，您应该向数据库添加一个唯一索引，以防止新记录在写入之前同时检查时通过验证：
class AddUniqueIndexToReleases < ActiveRecord::Migration
def change
add_index :releases, [:country, :medium], unique: true
end
end
class Release < ActiveRecord::Base
validates :country, uniqueness: { scope: :medium }
end
回答by Aamir
All the above answers are missing how to validate the uniqueness of multiple attributes in a model. The code below intends to tell how to use multiple attributes in a scope.
以上所有答案都缺少如何验证模型中多个属性的唯一性。下面的代码旨在说明如何在一个范围内使用多个属性。
validates :country, uniqueness: { scope: [:medium, :another_medium] }
It validates uniqueness of countryin all rows with values of mediumand another_medium.
这验证了独特的country与值的所有行medium和another_medium。
Note:Don't forget to add an index on the above column, this insures fast retrieval and adds a DB level validation for unique records.
注意：不要忘记在上面的列上添加索引，这可以确保快速检索并为唯一记录添加数据库级别的验证。
回答by K M Rakibul Islam
You can pass a :scopeparameter to your validator like this:
您可以:scope像这样将参数传递给验证器：
validates_uniqueness_of :medium, scope: :country
See the documentationfor some more examples.
有关更多示例，请参阅文档。
