Rails: 验证字符串的最小和最大长度，但允许它为空

我有一个领域，我想验证。我希望字段能够留空，但是如果用户输入数据，我希望它是某种格式的。目前我在模型中使用下面的验证，但是这不允许用户将其留空:

validates_length_of :foo, :maximum => 5
validates_length_of :foo, :minimum => 5

我如何写这个来完成我的目标？

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validates_length_of :phone, :in => 7..32, :allow_blank => true

:allow_blank - Attribute may be blank; skip validation.

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最佳答案

I think it might need something like:

validates_length_of :foo, minimum: 5, maximum: 5, allow_blank: true

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In your model e.g.

def validate
errors.add_to_base 'error message' unless self.foo.length == 5 or self.foo.blanc?
end

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every validates_* accepts :if or :unless options

validates_length_of :foo, :maximum => 5, :if => :validate_foo_condition

where validate_foo_condition is method that returns true or false

you can also pass a Proc object:

validates_length_of :foo, :maximum => 5, :unless => Proc.new {|object| object.foo.blank?}

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You can also use this format:

validates :foo, length: {minimum: 5, maximum: 5}, allow_blank: true

Or since your min and max are the same, the following will also work:

validates :foo, length: {is: 5}, allow_blank: true

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Or even more concise (with the new hash syntax), from the validates documentation:

validates :foo, length: 5..5, allow_blank: true

The upper limit should probably represent somehting more meaningful like "in: 5..20", but just answering the question to the letter.

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validates_length_of :reason, minimum: 3, maximum: 30

rspec for the same is

it { should validate_length_of(:reason).is_at_least(3).is_at_most(30) }

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How about that: validates_length_of :foo, is: 3, allow_blank: true

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Add in your model:

validates :color, length: { is: 7 }

color is a string:

t.string :color, null: false, default: '#0093FF', limit: 7