Using question mark character in Rails/ActiveRecord column name

Question

In keeping with Ruby's idiom of using a question mark in boolean methods (e.g. person.is_smart?), I'd like to do the same for an ActiveRecord field in Rails:

rails generate model Person is_smart?:boolean

I haven't actually run the above statement. I assume that database fields can't have a question mark in them. Will rails deal with this appropriately? Is the best practice to simply leave question marks off of models?

Using Rails 3.2.8

Solution 1

Rails will automatically generate the method smart? if there is a field named 'smart'.

Solution 2

One "gotcha" to be aware of if you happen to use :enum in your model, since this stores the value as an integer. The question mark attr method provided by active record expects to evaluate 0 or 1 as false / true respectively in the database. For example:

class Person
  enum mood: ['happy', 'sad', 'bored']
end

p = Person.new(mood: 'happy') # this would store mood as 0 in db
p.mood? #=> false

p.mood = 'sad' # saves as 1 in db
p.mood? #=> true

p.mood = 'bored' # saves as 2 in db
p.mood? #=> true

to see how this method works, see rails source

Comments

[matt]

Why not just call it smart and then add custom accessors so you can say is_smart? when you're talking to an actual Person?

[at.]

@matt - I guess that makes the most sense since it's not common that you would name a boolean variable with a question mark at the end and we would be treating the above is_smart? as a variable.

[oldergod]

Rails is your friend. See Cdesrosiers' answer.

[Kelvin]

Actually Rails generates ? methods for all columns. They appear to return true only if the value is truthy. So this is a perfect match for booleans.

[MCB]

I made an "ask/ answer" post on this topic after this answer, but I kept this as I think this information might be valuable for deciding how to name a bool column as well.

[Kyle Heironimus]

Actually, Kelvin's comment above is almost right. It returns true if the value is present?, not truthy. So "" returns false, for example.

[mwfearnley]

Is there any documentation for the semantics of the question-mark form?

[dre-hh]

never have been i so wrong. also thought it would just check for present? github.com/rails/rails/blob/master/activerecord/lib/…

[alex]

...and remember: it is a bad practice in rails to set prefixes like 'is_' or 'has_' in yours methods and columns stackoverflow.com/questions/37059547/…

[alex]

..and, until is a bad practice, actually it is possible at least in PosgreSQL and MySQL, to use question marks in the columns names which is very painful to use when you write it in a statement.

[vladpisanov]

Surprisingly, for numeric attributes, the question mark helper checks for 0. If user.level is 0, then user.level? is false but user.level.present? is true!

[illusionist]

its not that you cant call boolean cols without question mark. Its actually showing the actual value you stored in the col. add null: false, default: false clause in the migration.