KazydubB commented on a change in pull request #1870: DRILL-7359: Add support
for DICT type in RowSet Framework
URL: https://github.com/apache/drill/pull/1870#discussion_r352608433
##########
File path:
exec/vector/src/main/java/org/apache/drill/exec/vector/accessor/reader/UnionReaderImpl.java
##########
@@ -268,4 +274,51 @@ public String getAsString() {
}
return requireReader(type).getAsString();
}
+
+ private UnionReaderImpl getNullReader() {
+ AbstractObjectReader[] nullVariants = new
AbstractObjectReader[variants.length];
+ for (int i = 0; i < variants.length; i++) {
+ nullVariants[i] = variants[i].createNullReader();
+ }
+ return new NullUnionReader(schema(), unionAccessor, nullVariants);
+ }
+
+ private static class NullUnionReader extends UnionReaderImpl {
+
+ private NullUnionReader(ColumnMetadata metadata, VectorAccessor va,
AbstractObjectReader[] variants) {
Review comment:
Yes, this is for the case "where the `value` of a `key`/`value` pair is
null". This `value` can be `null` for a given `key` if the `key` is not present
in the dict for a given row (e.g. if you have a `Map<String, Integer>` with
entry `"a" : 1` and you try to `Map#get("b")`, with `Map` being a Java map in
the example). That is, the value may be non-nullable, but when you fetch a
`value` by `key` and there is no entry for the given key (in a row) then this
`Null*Reader` is used. The `Null*Reader`s are created in
https://github.com/apache/drill/pull/1870/files#diff-da401fee5976aec49192b5fb6e22de3eR83.
This structures are handled outside (of particular `DictReader`) so the
structure is retained for uniformity.
The "dummy" readers are not projected (merely a placeholder, aren't they?),
so this is not the way to use them(?).
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