How do attribute query methods work?

Question

I.e., is

Post.title?

equivalent to

Post.title.present?

Answer 1

No.

Object#present? is the same thing as calling !obj.blank?.

The "attribute?" method might end up calling the same code, but it might not, and it depends on the column type that you're dealing with.

The easiest way to see these not return the same value is to access a numeric column. Say you had foo.score as a decimal column in your db, and you set it to zero. You'd see the following behavior.

foo.score = 0
foo.score? # false
foo.score.present?  # true

The code for the "?" method is in ActiveRecord::AttributeMethods.

def query_attribute(attr_name)
  unless value = read_attribute(attr_name)
    false
  else
    column = self.class.columns_hash[attr_name]
    if column.nil?
      if Numeric === value || value !~ /[^0-9]/
        !value.to_i.zero?
      else
        return false if ActiveRecord::ConnectionAdapters::Column::FALSE_VALUES.include?(value)
        !value.blank?
      end 
    elsif column.number?
      !value.zero?
    else
      !value.blank?
    end 
  end 
end