code: public String encodeValue()
  	{
  		switch (function)
  		{
  			case EQ:
  				if (value != null && value.startsWith("_"))
  					return function.getPrefix() + value;
  				else
  					return value;
  			default:
  				if (function.hasBinaryParam())
  					return function.getPrefix() + value + ".." + value2;
  				else if (function.hasParam())
  					return function.getPrefix() + value;
  				else
  					return function.getPrefix();
  		}
  	}
docs: Encode this constraint in the query string value format
  
  @return