[GitHub] [druid] gianm commented on a change in pull request #12025: fix issues with multi-value string constant expressions

[GitBox <gi...@apache.org>]

gianm commented on a change in pull request #12025:
URL: https://github.com/apache/druid/pull/12025#discussion_r763307166



##########
File path: processing/src/main/java/org/apache/druid/segment/DimensionSelector.java
##########
@@ -164,6 +166,27 @@ static DimensionSelector constant(@Nullable final String value, @Nullable final
     }
   }
 
+  static DimensionSelector multiConstant(@Nullable final List<String> values)
+  {
+    if (values == null || values.isEmpty()) {
+      return NullDimensionSelectorHolder.NULL_DIMENSION_SELECTOR;
+    } else {
+      return new ConstantMultiValueDimensionSelector(values);
+    }
+  }
+
+  static DimensionSelector multiConstant(@Nullable final List<String> values, @Nullable final ExtractionFn extractionFn)
+  {
+    if (extractionFn == null) {
+      return multiConstant(values);
+    } else {
+      if (values == null) {
+        return constant(extractionFn.apply(null));

Review comment:
       What's the rationale behind doing this instead of `multiConstant(Collections.singletonList(extractionFn.apply(null))`?




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