code: public static function where($field, $operator, $value, $logical)
      {
          if (gettype($field)=="array") {
              throw new ClusterpointException("\"->where()\" function: passed field selector is not in valid format.", 9002);
          }
          if ($operator===null) {
              return "{$logical} {$field} ";
          } elseif ($value===null) {
              $value = $operator;
              $operator = '==';
          }
          if ($field instanceof Key) {
              $field =  self::field("{$field}");
          }
          if (!($value instanceof Raw)) {
          	if (is_string($value)){
  				$value = '"'.Client::escape($value).'"';
  			}
  			else {
  				$value =  json_encode($value);
  			}
          }
          return "{$logical} {$field}{$operator}{$value} ";
      }
docs: Pass back WHERE clause string to append the scope.
  
  @param  string  $field
  @param  string  $operator
  @param  mixed   $value
  @param  string  $logical
  @return string