Ruby Sequel model to have validation for create and not update

Question

How I can I avoid having validation for update while having it for create? For instance:

I wish to have an image field to have presence validation on create. But want to avoid it in edit and assume the previous value in case of no change.

Note: I am using Padrino.

Valedictorian

Answer 1

In Sequel, validations are generally done at the instance level using the validation_helpers plugin. So you just use a standard ruby conditional if you only want to validate it for new objects and not for existing ones:

plugin :validation_helpers
def validate
  super
  validates_presence :image if new?
end

Keane

Wow, didn't know that new? existed! Anyways great its a great ORM, thanks for it! – Valedictorian

Answer 2

you can say something like:

validates :image, :presence => true, on: :create

that means you will do validation only when do create.

Hexose

Answer 3

In Rails,

The "validates" keyword in Rails takes a parameter that allows you to do this:

validates :your_validator, :presence => true, :on => :create

You can also pass an array there:

validates :your_validator, :presence => true, :on => [:create, :update]

In Padrino,

I believe padrino using datamapper - DM has contextual validations. So, you could do a contextual validation.

validates :image, :presence => true, :when => [:custom]

Then while saving, you can do this:

post.save(:custom)
# OR
post.valid?(:custom)

The context :custom can be used in different places.

Unpleasantness

I think thats a Rails specific helper. I am using Padrino, my bad I should probably have mentioned. – Valedictorian

I didn't expect it to be a Padrino model :) I have updated my answer. I believe Padrino uses datamapper. – Unpleasantness

No, Padrino is ORM agnostic and I am using Sequel. Thanks for answering anyway. – Valedictorian