:greater_than_or_equal_to, :numericality, and other symbols with meaning

Question

A line of my of code is as follows:

validates :price, :numericality => {:greater_than_or_equal_to => 0.01}

:price is the only symbol that I defined. :numericality and :greater_than_or_equal_to both have some meaning of comparison.

1. What are these things called?
2. Where can I find documentation on them? There seems to be a ton of these symbols that do random things. Are these instance methods? Where can I find a list of them?

Answer 1

Symbols are like strings. They sometimes are used in constructions that look like method invocations, but they are not methods.

In your case, method validates accepts two parameters, a symbol and a hash. :numericality and :greater_than_or_equal_to are just keys in a hash, nothing more. What will validates do with them, no one knows (except validates itself). So, in order to find out, you need to read documentation on validates (and related rails guides, maybe).

Answer 2

The webpage here http://guides.rubyonrails.org/active_record_validations_callbacks.html should show what validations are available.

The symbols you refer to don't have a 'meaning' per se, but tell the methods what to do when passed as variables.

Validates is simply a method call, but in ruby the parentheses are option, sometimes putting them in makes it easier to conceptualise it, such as

validates(:price, :numericality => {:greater_than_or_equal_to => 0.01})