如果其他验证失败，Rails ActiveRecord在线状态验证是否有用？

Question

If I have validations that require certain values in a field, like a format: { with: some_regex } or an inclusion: { in: some_array } that will fail on blank or nil, is setting the validation presence: true useful in any way? In the same situation, is the length: { } validation useful if the other validations would fail?

Similarly, could a length validation of {1..n} preclude the need for a presence validation?

I'm trying to learn if there is something more going on or if the checks are simply redundant. For instance, the Rails Tutorial has a presence: true validation on the email address but the format validation should not allow a blank or nil address. Seems redundant, or is it style/convention?

Answer 1

If you're using something like format: regex and you can guarantee (easy enough through a unit test) that a blank or nil attribute will cause the whole record to be invalid, then yes you don't need to validate the presence. Same with the inclusion situation, and the length situation.

In general, adding more validations isn't necessarily a bad thing. But, if you've thoroughly tested your model for situations with blank or nil attributes and your current validations achieve the desired result, then you're fine.

Answer 2

Validation of presence if weaker then anything mentioned. I'd rather not put

validates presence: true

having, for instance,

validates format: { with: some_regex }, allow_blank: false

as the later already would cover the situation with the field having nil value.