验证 has_and_belongs_to_many 中的至少一个 [英] validate at least one in has_and_belongs_to_many

问题描述

我有一个模型:

has_and_belongs_to_many :users

如何验证模型中至少有一个用户?我试过了:

How do I validate that the model has at least one user in the model? I tried:

validates_presence_of :users

但这似乎并没有给我想要的...

But that doesn't seem to give me what I want...

推荐答案

我会编写自定义验证:

validate :has_users?

def has_users?
  # rails 2:
  errors.add_to_base "Model must have some users." if self.users.blank?
end

那正是这样做的.

注意在 rails 3+ 中你必须使用:

Note in rails 3+ you have to use:

  # rails 3+
  errors.add :base, "Model must have some users." if self.users.blank?

在 rails 4+ 中有一个内置的快捷方式，所以你可以简单地做:

In rails 4+ there's a built-in shortcut, so you can simply do:

validates :users, presence: true

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