Mark Payne created NIFI-16478:
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Summary: Nested arrays are written as Java object strings when a
CHOICE includes an array of strings
Key: NIFI-16478
URL: https://issues.apache.org/jira/browse/NIFI-16478
Project: Apache NiFi
Issue Type: Bug
Components: Extensions
Reporter: Mark Payne
Assignee: Mark Payne
When a field's schema is a CHOICE between an array of strings and a nested
array of records, values such as {{[[[]], [[{"key":"a"}]]]}} can be written as
strings like {{"[[Ljava.lang.Object;@4613311f]"}} instead of keeping their
nested structure. This happens, for example, when ConsumeKafka uses "Continue
with Merged Schema" and one message has an empty array ({{[]}}, inferred as an
array of strings) while another has nested arrays of records for the same field.
{{DataTypeUtils.chooseDataType}} considers both choices compatible because any
{{Object[]}} is accepted as a String. Re-inferring the value's type does not
match either choice, so it falls back to the first compatible choice. When that
choice is the array of strings, each inner array is converted with
{{Arrays.toString}}.
When no choice is a clear match, {{chooseDataType}} should prefer a choice that
does not convert nested arrays, collections, or maps into Strings.
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