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When setting up my models I often find myself having to write out all of its attributes when setting up certain validations. A common example is when I use the presence parameter:

validates :first_name, :last_name, :username, :email, presence: true

Is there a clever way to select all of its attributes without explicitly writing them all out similar to how you can retrieve them in the rails console?

User.columns

And pass it as an argument in the validates method?

ALL_ATTRIBUTES = User.columns

validates ALL_ATTRIBUTES, presence: true

Trying something like this out I got this error undefined method 'to_sym'

Carl Edwards
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2 Answers2

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I will NOT encourage you or anyone to do this. Reason being when you run into issues, when an object of your model doesn't get saved and throw errors because of a new column which was added to application after some time in future, and you or new developers will wonder WHY?!?!.

However, if you must do then here you go:

validates *self.column_names.map(&:to_sym), presence: true

Here, * in Ruby is known as splat operator and here's the explanation on &:.

Community
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Surya
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  • Thanks for the warning and yes this seems to do the trick. Just a few questions. Why the `*` before self and `&:` before converting the attributes to symbols? – Carl Edwards Oct 04 '14 at 14:24
  • @CarlEdwards `column_names.map(&:to_sym)` is shorthand for `column_names.map { |column| column.to_sym }`. If you are only calling a method on the attributes, then you can shorten is to use `&:to_sym`. It's syntactic sugar. – Mohamad Oct 04 '14 at 14:28
  • @CarlEdwards: added explanation of your doubts. If an answer helps then please accept it so others can use it for reference. Thanks. – Surya Oct 04 '14 at 14:29
  • Thanks so much for the clear explanation and fair warning against using this approach. – Carl Edwards Oct 04 '14 at 14:31
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This is an awful idea. But you can do it this way:

attrs = column_names.map { |column| column.to_sym }
validates *attrs, presence: true

Why is it a bad idea? Because it's not very clear what is being validated it. It makes debugging hard, and could cause you have strange bugs. If you add a column in the future that does not require presence validation, you will trip up. Also, some things my not require presence. For example, an email field will need a regex validation, which automatically knows that a blank string is invalid. So a presence validator is redundant.

Beware of being too clever, as it's sometimes not so clever after all.

Mohamad
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  • I ended up getting this: `undefined method 'to_sym' for [:id, :name, :position, :visible, :created_at, :updated_at]:Array` – Carl Edwards Oct 04 '14 at 14:17