nbruno commented on a change in pull request #9151:
URL: https://github.com/apache/arrow/pull/9151#discussion_r565615777
##########
File path: java/vector/src/main/codegen/templates/UnionFixedSizeListWriter.java
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@@ -169,6 +169,29 @@ public StructWriter struct(String name) {
return structWriter;
}
+ @Override
+ public MapWriter map() {
+ return writer;
+ }
+
+ @Override
+ public MapWriter map(String name) {
+ MapWriter mapWriter = writer.map(name);
+ return mapWriter;
+ }
+
+ @Override
+ public MapWriter map(boolean keysSorted) {
+ writer.map(keysSorted);
Review comment:
I had originally thought this too, but making this change will cause the
new unit tests I added for MapWriter to break (it won't correctly write a list
of maps).
I believe it is because of how List and Map vectors are implemented. Map
itself does not store any data, it is a subclass of List, delegating storage to
the parent. When we have a list and want to write a map value to get
`List<Map<?, ?>>`, we don't need a new writer with a new vector to write into,
we actually want to reuse the vector of the current list. If we construct a new
writer and return that, we would end up with `List<List<Map<?, ?>>>` when we
really want `List<Map<?,?>>`.
My explanation probably isn't 100% clear or correct, but it's how I was able
to figure out how to implement MapWriter for this PR.
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