NIFI-7462: QueryRecord cast functions for Choice datatypes

[pcgrenier]

QueryRecord cast functions for Choice datatypes

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[markap14]

Will review

[markap14]

Hey @pcgrenier thanks for putting this PR up. I do think that it addresses the case when all of the values coming in have the same type. But if your schema says that field 'num' can be either an int or a float, this solutions forces the user to cast all values to either int or float. It stands to reason that with such a schema, you could have a mix of both ints and floats. And depending on the query, we may want to keep these values as such.

I also would like to avoid adding our own custom "cast" functions when cast functions already exist in SQL. I definitely feel like that's a red flag that we're not doing something quite right.

So I have a proposal that I think addresses this well but does so very differently. In the FlowFileTable class, we define the data types that Calcite should use internally for each of the types. For the CHOICE data type, we just blindly return typeFactory.createJavaType(Object.class) and that's why it fails - you can't cast an Object to a float, double, int, etc. So I think the better solution is to refine what we return for CHOICE types. Specifically, if we have a choice between two types of numbers where one is wider than the other, we should return the wider type (e.g., for a double/float we should return double). For two numbers where one is not wider than the other (e.g., double/int) we should return a String, as String is considered wider than both of these. For other cases, (e.g., double/Record) we should return Object as we do now.

[markap14]

I don't think we want to be getting the 'cause' for the general Exception - we should log the exception itself. We get the cause for SQLException only because we know that it's generally wrapping another exception.

[pcgrenier]

Yeah, this one was a strange one. Since the calcite cast function throwing the cannot handle Object exception was getting trapped here and the message was super vague so had to dig into the app logs to see the stack trace.

[markap14]

Yeah unfortunately for this processor, when an Exception is thrown it's kind of difficult to figure out without the logs. But if we were to unwrap the cause, that could make even the logs confusing, which is even worse.

[markap14]

@pcgrenier I created a new PR based off of yours - #4282. Can you review that and make sure that it gives you what you need? This will allow the table schema to be more intelligent for CHOICE types and in cases like this it will allow you to use proper SQL CAST functions and also allows you to perform functions like SUM() without the need to explicitly cast them, which is important if your data does have mixed data types.

[pcgrenier]

Closing in favor of #4282