build_relation

# File activerecord/lib/active_record/validations/uniqueness.rb, line 58
      def build_relation(klass, attribute, value)
        if reflection = klass._reflect_on_association(attribute)
          attribute = reflection.foreign_key
          value = value.attributes[reflection.klass.primary_key] unless value.nil?
        end

        if value.nil?
          return klass.unscoped.where!(attribute => value)
        end

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

        attribute_name = attribute.to_s
        value = klass.predicate_builder.build_bind_attribute(attribute_name, value)

        table = klass.arel_table
        column = klass.columns_hash[attribute_name]

        comparison = if !options[:case_sensitive]
          # 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
        klass.unscoped.where!(comparison)
      end