jbonofre commented on code in PR #1379:
URL: https://github.com/apache/arrow-java/pull/1379#discussion_r4492168592
##########
vector/src/main/java/org/apache/arrow/vector/types/Types.java:
##########
@@ -164,7 +164,7 @@ public enum MinorType {
@Override
public FieldVector getNewVector(
Field field, BufferAllocator allocator, CallBack
schemaChangeCallback) {
- return new NullVector(field.getName());
+ return new NullVector(field);
Review Comment:
This change makes a `NullVector` created from a schema keep its nullability.
But `NullVector` transfer pairs still create a plain nullable vector
(`TransferImpl(String ref)` -> `new NullVector(ref)`, and
`getTransferPair(Field, ...)` only uses `field.getName()`). So the source and
target of a transfer now have different fields.
That breaks code that worked before. `VectorSchemaRoot.slice()` uses
`getTransferPair(allocator)`, and `VectorSchemaRootAppender` compares
nullability, so this now throws `IllegalArgumentException: Vector schema roots
have different schemas.`:
```java
Schema schema = new Schema(List.of(
new Field("n", FieldType.notNullable(ArrowType.Null.INSTANCE), null)));
try (VectorSchemaRoot root = VectorSchemaRoot.create(schema, allocator);
VectorSchemaRoot target = VectorSchemaRoot.create(schema, allocator)) {
root.setRowCount(3);
try (VectorSchemaRoot slice = root.slice(0, 2)) {
VectorSchemaRootAppender.append(target, slice);
}
}
```
Before this PR, both sides were nullable, so this worked.
Could you also update `NullVector` so its transfer pairs keep the field?
Something like:
```java
@Override
public TransferPair getTransferPair(String ref, BufferAllocator allocator) {
return new TransferImpl(new NullVector(ref, field.getFieldType()));
}
@Override
public TransferPair getTransferPair(Field field, BufferAllocator allocator) {
return new TransferImpl(new NullVector(field));
}
```
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