[PythonReports-users] SQLAlchemy optional relationships - what is recommended way to handle

[Werner F. B. <wer...@fr...>]

Hi Alex,

O.K. redid my report using the Tk designer and added a few fields and 
preview - success:-) .

Now to my question I define my fields like this:

"drinkinfo.subregion_lv.name" and my "data" contains a few entries of 
type "cellarbook" each of them has "drinkinfo" relation and it I have 
things like "country_lv", "subregion_lv" etc etc, some of them are 
optional, i.e. not present on all rows.  How should that be defined in 
the "expr"?

Could I call a method of my own, something along these lines:

def getRelInfo(objval, sainst):
     """Get related information

     :param objval: e.g. "drinkinfo.someoptionalrel.name"
     :param sainst: an SA Instance of the row, e.g. a "cellarbook" entry/row
     :return: the column value or blank

     """
     try:
         newAttr = sainst

         parts = objval.attribute_name.split(".")
         rel, colname = (parts[:-1], parts[-1:][0])

         for r in rel:
             if newAttr:
                 with no_autoflush(wx.GetApp().ds):
                     newAttr =  getattr(newAttr, r)

         if newAttr:
             return getattr(newAttr, colname)
         else:
             return ""

Thanks for hints, or links to documentation or a examples.

Werner