avoiding csv write if not necessary workout edit view

rowers/views/workoutviews.py

@@ -3451,7 +3451,7 @@ def workout_edit_view(request,id=0,message="",successmessage=""):
             except UnknownTimeZoneError:
                 thetimezone = 'UTC'
 
-
+            timechanged = (startdatetime != row.startdatetime)
 
             row.name  = name
             row.date = date
@@ -3484,19 +3484,21 @@ def workout_edit_view(request,id=0,message="",successmessage=""):
                 add_workouts_plannedsession([row],ps,row.user)
 
             # change data in csv file
+            datachanged = (dragchanged or timechanged)
+            if datachanged:
+                r = rdata(row.csvfilename)
+                if dragchanged:
+                    try:
+                        r.change_drag(newdragfactor)
+                    except AttributeError:
+                        pass
 
-            r = rdata(row.csvfilename)
-            if dragchanged:
-                try:
-                    r.change_drag(newdragfactor)
-                except AttributeError:
-                    pass
+                if r == 0:
+                    return HttpResponse("Error: CSV Data File Not Found")
+                r.rowdatetime = startdatetime
+                r.write_csv(row.csvfilename,gzip=True)
+                dataprep.update_strokedata(encoder.decode_hex(id),r.df)
 
-            if r == 0:
-                return HttpResponse("Error: CSV Data File Not Found")
-            r.rowdatetime = startdatetime
-            r.write_csv(row.csvfilename,gzip=True)
-            dataprep.update_strokedata(encoder.decode_hex(id),r.df)
             successmessage = "Changes saved"
 
             if rankingpiece: