code: function find(model, id, tx, callback) {
      var
          sql,
          select,
          where,
          append,
          params,
          parsed,
          complexFind = typeof id === 'object';
      if (complexFind) {
          parsed = parseFindOptions(model, id, true);
  
          select = parsed.select;
          where = parsed.where;
          append = parsed.append;
          params = parsed.params;
      } else {
          // by primary key:
          select = model.__selectAttributesNames;
          where = '`' + model.__primaryKey + '`=?';
          append = '';
          params = [id];
      }
      sql = utils.format('select %s from `%s` where %s %s', select, model.__table, where, append);
      smartRunSQL(model.__pool, sql, params, tx, function (err, results) {
          if (err) {
              return callback(err);
          }
          if (results.length > 1) {
              return callback(new Error('Multiple results found.'));
          }
          return callback(null, results.length === 0 ? null : model.__warp.__createInstance(model, results[0]));
      });
  }
docs: find one and only one results by id or options: