验证与validate_uniquess_of？

Question

Is there a difference between using

validates :foo, uniqueness: true

or

validates_uniqueness_of :foo ?

I know this is a simple questions, but Google didn't help

When and why should one be used over the other?

Answer 1

The validates method is a shortcut to all the default validators that Rails provides. So, validates :foo, uniqueness: true would trigger UniquenessValidator under the hood. The source code for validates can be found in the API doc here . As shown there, it basically triggers the validators of the options passed and raises an error in case an invalid option is passed. validates_uniqueness_of also triggers the UniquenessValidator , the same as validates . Its source code is

# File activerecord/lib/active_record/validations/uniqueness.rb, line 233
  def validates_uniqueness_of(*attr_names)
    validates_with UniquenessValidator, _merge_attributes(attr_names)
  end

The only difference is that with validates_uniqueness_of , we can ONLY validate the uniqueness and not pass additional options, whereas validates accepts multiple options. So we could have the following validations with validates :

validates :name, presence: true, uniqueness: true, <some other options>

But the same would not be possible with validates_uniqueness_of .