jbonofre commented on code in PR #1381:
URL: https://github.com/apache/arrow-java/pull/1381#discussion_r4493107342
##########
vector/src/main/codegen/templates/DenseUnionVector.java:
##########
@@ -631,6 +631,7 @@ private void createTransferPairs() {
to.childVectors[i] = dstVec;
internalTransferPairs[i] = srcVec.makeTransferPair(dstVec);
}
+ to.nextTypeId = nextTypeId;
Review Comment:
This cause a regression for unions whose type ids aren't `0..n-1`, for
example `[5, 10]`, which is what IPC or the C Data interface gives us when the
schema declares type ids.
`createTransferPairs` fills `to.childVectors` at the loop index (0 and 1),
but `setChildVectorValueCounts` reads `childVectors[typeMapFields[i]]`, i.e.
`childVectors[5]` and `childVectors[10]`, which are null on the target. Before
this change `to.nextTypeId` was 0, so that loop never ran. Now any
`setValueCount` on the target after `transfer()` (including through
`VectorSchemaRoot.setRowCount`) throws:
```
java.lang.NullPointerException: Cannot invoke
"org.apache.arrow.vector.ValueVector.setValueCount(int)" because
"this.childVectors[...]" is null
at
org.apache.arrow.vector.complex.DenseUnionVector.setChildVectorValueCounts(DenseUnionVector.java)
at
org.apache.arrow.vector.complex.DenseUnionVector.setValueCount(DenseUnionVector.java)
```
Here's an example to reproduce the regression:
```java
Field field =
new Field(
"u",
FieldType.nullable(new ArrowType.Union(UnionMode.Dense, new int[]
{5, 10})),
asList(
Field.nullable("i", MinorType.INT.getType()),
Field.nullable("b", MinorType.BIT.getType())));
try (DenseUnionVector vector = (DenseUnionVector)
field.createVector(allocator)) {
vector.allocateNew();
vector.setTypeId(0, (byte) 5);
vector.setSafe(0, intHolder(5));
vector.setTypeId(1, (byte) 10);
vector.setSafe(1, bitHolder(true));
vector.setTypeId(2, (byte) 5);
vector.setSafe(2, intHolder(7));
vector.setValueCount(3);
TransferPair pair = vector.getTransferPair(allocator);
try (DenseUnionVector target = (DenseUnionVector) pair.getTo()) {
pair.transfer();
target.setValueCount(3); // NPE
}
}
```
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