Hi 
I recently needed to validate that an attribute on one of my models is a multiple of certain value. Having looked through the numericality validation docs, it doesn’t seem like there’s a way to do this without writing a custom validation. My requirement as a custom validation is something like:
class MyModel
validates :offset, numericality: { only_integer: true }
validate :offset_is_a_multiple_of_seven
private
def offset_is_a_multiple_of_seven
# multiple_of? is defined on Integer by ActiveSupport
return if offset.multiple_of?(7)
errors.add(:offset, "must be a multiple of 7)
end
end
I thought it might be useful if the numericality validator handled this. Example:
class MyModel
validates_numericality_of :offset, multiple_of: 7
end
model = MyModel.new
model.offset = -7
model.valid? # => true
model.offset = 0
model.valid? # => true
model.offset = 7
model.valid? # => true
model.offset = 10
model.valid? # => false
Example for positive values only:
class MyModel
validates_numericality_of :offset, multiple_of: 7, greater_than: 0
end
model = MyModel.new
model.offset = -7
model.valid? # => false
model.offset = 0
model.valid? # => false
model.offset = 7
model.valid? # => true
model.offset = 10
model.valid? # => false
I thought I’d create this topic to check if this is a generic enough requirement to implement. I’ve already got a PR implementing this if the feedback is positive.
