build_relation

# File activerecord/lib/active_record/validations/uniqueness.rb, line 53
      def build_relation(klass, table, attribute, value) #:nodoc:
        if reflection = klass._reflect_on_association(attribute)
          attribute = reflection.foreign_key
          value = value.attributes[reflection.klass.primary_key] unless value.nil?
        end

        # the attribute may be an aliased attribute
        if klass.attribute_alias?(attribute)
          attribute = klass.attribute_alias(attribute)
        end

        attribute_name = attribute.to_s

        column = klass.columns_hash[attribute_name]
        cast_type = klass.type_for_attribute(attribute_name)
        value = cast_type.serialize(value)
        value = klass.connection.type_cast(value)

        comparison = if !options[:case_sensitive] && !value.nil?
          # will use SQL LOWER function before comparison, unless it detects a case insensitive collation
          klass.connection.case_insensitive_comparison(table, attribute, column, value)
        else
          klass.connection.case_sensitive_comparison(table, attribute, column, value)
        end
        if value.nil?
          klass.unscoped.where(comparison)
        else
          bind = Relation::QueryAttribute.new(attribute_name, value, Type::Value.new)
          klass.unscoped.where(comparison, bind)
        end
      rescue RangeError
        klass.none
      end