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.primary_key_column.name]
        end

        column = klass.columns_hash[attribute.to_s]
        value  = klass.connection.type_cast(value, column)
        value  = value.to_s[0, column.limit] if value && column.limit && column.text?

        if !options[:case_sensitive] && value && column.text?
          # will use SQL LOWER function before comparison, unless it detects a case insensitive collation
          klass.connection.case_insensitive_comparison(table, attribute, column, value)
        else
          value = klass.connection.case_sensitive_modifier(value) unless value.nil?
          table[attribute].eq(value)
        end
      end