验证有条件时，数据库中的唯一性验证

问题描述

当有多个进程时，在Rails中使用唯一性验证是不安全的，除非在数据库上也强制执行约束（在我的情况下是PostgreSQL数据库，所以请参阅）。

Using uniqueness validations in Rails is not safe when there are multiple processes unless the constraint is also enforced on the database (in my case a PostgreSQL database so see http://robots.thoughtbot.com/the-perils-of-uniqueness-validations).

在我的情况下，唯一性验证是有条件的：只有在模型中的另一个属性变为true时才应强制执行。所以我有

In my case, the uniqueness validation is conditional: it should only be enforced if another attribute in the model becomes true. So I have

class Model < ActiveRecord::Base
  validates_uniqueness_of   :text, if: :is_published?

  def is_published?
    self.is_published
  end
end

所以模型有两个属性： is_published （布尔值）和文本（文本属性）。 text 在所有类型 Model iff is_published 是真的。

So the model has two attributes: is_published (a boolean) and text (a text attribute). text should be unique across all models of type Model iff is_published is true.

使用过于拘束，因为无论的值如何，它都会强制执行约束is_published 。

Using a unique index as suggested in http://robots.thoughtbot.com/the-perils-of-uniqueness-validations is too constraining because it would enforce the constraint regardless of the value of is_published.

是否有人知道PostgreSQL数据库中的条件索引？还是另一种解决方法？

Is anyone aware of a "conditional" index on a PostgreSQL database? Or another way to fix this?

推荐答案

是的，使用。

CREATE UNIQUE INDEX tbl_txt_is_published_idx ON tbl (text) WHERE is_published;

示例：



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