How are values cast when assigning to a Boolean field in Rails ActiveRecord?

Question

Short version of my question

In Rails ActiveRecord, if I have a Boolean field and I assign it something like \"abc\" or 2, the

Answer 1

The behavior of boolean columns changed with two commits:

• e01a46f (2014-10-17)
• a502703 (2015-01-04).

The new rule is very simple. See the code below:

module ActiveRecord
  module Type
    class Boolean < Value # :nodoc:
      def type
    :boolean
      end

      private

      def cast_value(value)
    if value == ''
      nil
    else
      !ConnectionAdapters::Column::FALSE_VALUES.include?(value)
    end
      end
    end
  end
end

The constant ConnectionAdapters::Column::FALSE_VALUES is defined as follows:

[false, 0, '0', 'f', 'F', 'false', 'FALSE', 'off', 'OFF'].to_set

If a value is not an empty string and is not among them, it will be cast to true.

This change will become effective on the Rails 5.0.

Answer 2

This is a Ruby thing rather than a Rails thing. Boolean is "truthy". There's a pretty useful article on it here. https://gist.github.com/jfarmer/2647362

Answer 3

This is done in the bowels of ActiveRecord: specifically with

ActiveRecord::ConnectionAdapters::Column.value_to_boolean

at least in my version of rails (it may be somewhere slightly different in more recent versions).

Here's the source in my version

    # File activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb, line 144
    144:         def value_to_boolean(value)
    145:           if value.is_a?(String) && value.blank?
    146:             nil
    147:           else
    148:             TRUE_VALUES.include?(value)
    149:           end
    150:         end

where TRUE_VALUES is defined as

#activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb:10:      
TRUE_VALUES = [true, 1, '1', 't', 'T', 'true', 'TRUE'].to_set

1, 0, "f" and "t" are there because of popular DBMS's like MySql & PostgreSql, which store bools as 0/1 and "f"/"t" respectively.

It's worth noting the difference between this and what passes an "if" test in Ruby/Rails, ie values that are "truthy" or "falsy" ("falsy" values will fail an if test, "truthy" values will pass it).

In Ruby, nil and false are "falsy" and literally anything else (including 0, empty arrays, empty strings, empty hashes etc) is "truthy". So, there's a massive disparity between what is deemed truthy/falsy in ruby and what is saved as true/false to a boolean database column.