[TDVT Failure] "Illegal use of NULL"

[pvanderknyff]

It looks like Dremio does not support untyped nulls (from thiscommunity post), which means that you need to cast the null as something. You can do that in the dialect function, we have an example here.

This affects the operator.bool test, there is one failed test that throws this error on the Dremio side.

[kylep-dremio]

@pvanderknyff see https://github.com/dremio-hub/tableau-connector/blob/master/dialect_plugin.tdd#L1097 - this doesn't seem to affect the results.

[pvanderknyff]

Hi Kyle. Apologies for not responding earlier, was out of office last week. You also need to set the default case to cast the null as an int, I'm looking into how to do that for a custom dialect. I'll keep you updated.

[pvanderknyff]

Ok, the real way to solve this is to add <local-type name='null' value='CAST(NULL AS INTEGER)' />, since this test case is for null by itself. Unfortunately, our code does not parse local-type = null. I've put a story on our backlog to address this, but for now, a workaround is to try:
<local-type name='error' value='CAST(NULL AS INTEGER)' />

Note that using local-type error is a hacky workaround meant to unblock this case, and should not be used in other cases. It only works here because null is limited in scope.

Let me know if this works, or if you have any other questions.

[kylep-dremio]

@pvanderknyff unfortunately adding that line into 2019.4.2 results in the connector no longer being loaded into Tableau. Will check with 2020.1 when I get a sec...

[kylep-dremio]

More info, same problem with 2020.1
{"ts":"2020-03-13T14:29:37.809","pid":22486,"tid":"72c74","sev":"warn","req":"-","sess":"-","site":"-","user":"-","k":"msg","v":"LoadDialectFromXML: Malformed XML file: dialect_plugin.tdd"} {"ts":"2020-03-13T14:29:37.810","pid":22486,"tid":"72c74","sev":"warn","req":"-","sess":"-","site":"-","user":"-","k":"msg","v":"Showing first 5 errors:\nError(1098,67): value 'error' not in enumeration (id: )"} {"ts":"2020-03-13T14:29:37.810","pid":22486,"tid":"72c74","sev":"error","req":"-","sess":"-","site":"-","user":"-","k":"connector-plugin-error","e":{"log-code":"0e9a88a9","log-source":"needs-classification"},"v":"Error loading dialect file (.tdd) for class 'dremio'. Skipping plugin."}

[pvanderknyff]

Short story: I think we can ignore this for now, and move on to the other tests.

Longer story: I double checked, and it looks like that local type error is not actually in the XSD's like I thought. Since this is the only null test you failed, and it looks like it can't be fixed in the SDK at this moment, I'd say move on to the other tests.

Play around in Tableau with boolean fields with null fields (the calcs table in TestV1 has some) to make sure the error isn't thrown naturally, but I think this is a rare occurrence only possible in calculated fields and shouldn't be a big deal, thus, we are safe enough ignoring it for now.

We do have this trouble with a couple other connectors we wrote before the SDK, so we know how to fix it, we just need to expose that to the SDK. I've put a story on our backlog to do that in a one of our future sprints.

[kylep-dremio]

Thanks Patrick.