Here are some of my findings. I gathered them here to hopefully help others. I hope they are correct, but I can’t guarantee it. These are based on using the XType as a tag, I haven’t yet delved into direct calls from other services/processing. This is based on 5.0.2 plus commits up to 3625c02.
If one raises a CannotCalculate in the XType get_scalar, for the time periods ‘$current’ and ‘$latest’, it will bubble up to the ‘tag’ layer where it will become a ‘None’ value. For the get_aggregation, the CannotCalculate is not caught and will bubble all the way, causing report generation to halt. Based on the above behavior, I am catching any CannotCalculate from a get_scalar call and returning a ‘None’ value from get_aggregation. Based on the above two observations, if get_scalar raises a CannotCalculate exception due to missing data that is required, a debug message is logged. If it is for some other reason, an error debug message is logged. Errors might be due to bad configuration. I’m currently looking at if it is possible to detect all of these at start up. The only way to break out of the XType get_aggregation is to return a value. In my case the ‘sum’ aggregate does not make much sense. But if I don’t return a value the XTypeTable will perform it (assuming I have prepended my XType into the system). Since I can easily calculate the ‘sum’, I do… (See below, I don’t think there is any benefit to my implementation. But its my XType and I want control… ha ha. Well it does stop the XType system for looking for an implementation) Some of the aggregation types supported by XTypeTable can be ‘expensive’. One may/should prepend the Xtype to ‘override’ these. This is because the ‘default’ has to loop through and calculate all the values in the interval. In my case, only calculating the ‘sum’ and ‘avg’ require this. Others could be computed after a single sql query. I’ll post any other findings/ramblings/corrections I find. Hope this helps someone. rich -- You received this message because you are subscribed to the Google Groups "weewx-development" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/weewx-development/61b661a1-f6ae-4d12-8bd4-6ecc36e9186bn%40googlegroups.com.
