docs: function (keyColumn, valueColumn, cb) {
              var ret = new Promise(), map = {};
              if (isFunction(valueColumn)) {
                  cb = valueColumn;
                  valueColumn = null;
              }
              var k = this.__hashIdentifierToName(keyColumn), v = this.__hashIdentifierToName(valueColumn);
              return this.map(function (r) {
                  map[r[k]] = v ? r[v] : r;
              }).chain(function () {
                  return map;
              }).classic(cb).promise();
          }