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_r353132642
##########
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:
Regarding points of your suggestion:
- `DictReaderImpl` has `NullStateReaders.REQUIRED_STATE_READER`
`NullStateReader`, i.e. it can't be `NULL` (like `MapReader`).
- `DICT` can't have `NULL` key as it is `REQUIRED`.
- If the `DICT` has a key, but the value is `NULL`, then `isNull()` for the
value returns `true` - yes.
- in the (tricky) case of a missing key from the `DICT`, the latter approach
was taken - there is no differentiation between missing key and `NULL` value.
(The new `Null*Reader`s are introduced to be used in the case of a missing key
- their `isNull()` always returns `true`; note, that in case when a key is
present and the value is `NULL`, current (non-null) readers' `isNull()` will
return `true` for that particular position, as corresponding value reader keeps
track of nullability). The former approach was discarded to ensure uniform
behavior without a chance of getting `NPE` or making `null`-checks.
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