paul-rogers 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_r352737013
##########
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:
We may want to define our semantics here. If I understand your description,
we have:
* The entire `DICT` is `NULL` (is this allowed)?
* The `DICT` has an entry for key `x`, but the value is null.
* The `DICT` has an entry for the `NULL` key.
* The `DICT` has no entry for the key `x`, meaning that the value is
implicitly `NULL`.
We have similar situations with the `UNION` type, perhaps we can learn from
that:
* The entire `UNION` can be `NULL`.
* The `UNION` can have an entry for, say, `VARCHAR`, but the `VARCHAR` is
`NULL`.
* The `UNION` does not have an entry for a given type (say, `INT`), so the
value is implicitly `NULL`. (Although we don't allow access to such a type.)
My suggestion would be that we use the `isNull()` method for all the `NULL`
cases:
* If the `DICT` is `NULL` for a row, then `isNull()` returns true for the
`DICT` reader.
* If the `DICT` has a `NULL` key, then the key `isNull()` for the key
returns true.
* If the `DICT` has a key, but the value is `NULL`, then `isNull()` for the
value returns true.
Now the tricky case: a key is missing from the `DICT`:
* If the `DICT` does not have a key, then we may want a `hasKey()` method,
and the value reader should be a Java `null` because it does not exist.
Or:
* If the `DICT` does not have a key, then the value reader's `isNull()`
returns true. (This means we cannot differentiate the has-key-with-null-value
vs. does-not-have-a-key cases.)
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