Allow Ransack to include NULL values in "does not equal" searches.

lib-gem_ext-arel-predications.rb

module Arel
  module Predications
    def not_eq other
      if other.is_a? Nodes::Not
        Nodes::Equality.new self, other.value
      else
        Nodes::NotEqual.new self, other
      end
    end

    def eq other
      if other.is_a? Nodes::Not
        Nodes::NotEqual.new self, other.value
      else
        Nodes::Equality.new self, other
      end
    end

    def matches other
      if other.is_a? Nodes::Not
        Nodes::DoesNotMatch.new self, other.value
      else
        Nodes::Matches.new self, other
      end
    end

    def does_not_match other
      if other.is_a? Nodes::Not
        Nodes::Matches.new self, other.value
      else
        Nodes::DoesNotMatch.new self, other
      end
    end
  end
end

lib-gem_ext-ransack-constants.rb

# Include NULL values in NOT queries
# https://github.com/ernie/ransack/issues/123
module Ransack
  module Constants
    HACKED_PREDICATES = [
      ['not_eq', {:arel_predicate => 'eq_any', :formatter => proc { |v| [Arel::Nodes::Not.new(v), nil] }}],
      ['does_not_match', {:arel_predicate => 'matches_any', :formatter => proc { |v| [Arel::Nodes::Not.new(v), nil] }}]
    ]

    AREL_PREDICATES.delete('not_eq')
    AREL_PREDICATES.delete('does_not_match')
    DERIVED_PREDICATES.concat(HACKED_PREDICATES)
  end
end