[avro] Fix ClassCastException when writing MULTISET with non-string element type - #9066
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JingsongLi merged 1 commit intoAug 6, 2026
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…lement type AvroSchemaConverter routes MULTISET and MAP through the same branch, so a multiset with a non-string element is encoded as an array of key-value records. AvroSchemaVisitor only recognized MapType there and cast every other type to the final class ArrayType, so any MultisetType failed. Handle MultisetType in the ARRAY branch by reusing the converter's own extractKeyTypeToAvroMap/extractValueTypeToAvroMap, keeping schema creation and schema visiting on one source. Also correct the Avro type mapping table for MAP and MULTISET in fileformat.md. Generated-by: Claude Code
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Purpose
fix #9064
AvroSchemaConverterhandlesMULTISETandMAPin one branch, so a non-string element gets the array-of-record encoding.AvroSchemaVisitor.visit()recognized onlyMapTypein itsARRAYbranch and cast everything else to thefinalclassArrayType, so anyMULTISETwith a non-string element threwClassCastExceptionon write and read, even thoughvalidateDataFieldspassed. ORC and Parquet already accept that schema.extractKeyTypeToAvroMap/extractValueTypeToAvroMapthere, keeping schema creation and visiting on one source. The converter is untouched, so the written encoding is unchanged.MAP/MULTISETrows infileformat.md: theMAProw says the key must be a string type, butFormatReadWriteTest'snonStrKeyMap = MAP(INT, ...)already passes on avro.Tests
AvroFormatReadWriteTest#testMultisetWithNonStringElement(round trip; throws without the fix) and#testMultisetWithStringElement(regression guard).mvn -pl paimon-format -DfailIfNoTests=false clean install— 531 tests passed, 0 failures. No existing test usedMULTISET.