[GitHub] [iceberg] wmoustafa commented on a diff in pull request #4242: Support non-optional union types for Avro

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

wmoustafa commented on code in PR #4242:
URL: https://github.com/apache/iceberg/pull/4242#discussion_r871148920


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core/src/main/java/org/apache/iceberg/avro/AvroSchemaWithTypeVisitor.java:
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@@ -79,11 +79,29 @@ private static <T> T visitRecord(Types.StructType struct, Schema record, AvroSch
   private static <T> T visitUnion(Type type, Schema union, AvroSchemaWithTypeVisitor<T> visitor) {
     List<Schema> types = union.getTypes();
     List<T> options = Lists.newArrayListWithExpectedSize(types.size());
-    for (Schema branch : types) {
-      if (branch.getType() == Schema.Type.NULL) {
-        options.add(visit((Type) null, branch, visitor));
-      } else {
-        options.add(visit(type, branch, visitor));
+
+    // simple union case
+    if (AvroSchemaUtil.isOptionSchema(union)) {
+      for (Schema branch : types) {
+        if (branch.getType() == Schema.Type.NULL) {
+          options.add(visit((Type) null, branch, visitor));
+        } else {
+          options.add(visit(type, branch, visitor));
+        }
+      }
+    } else { // complex union case
+      Preconditions.checkArgument(type instanceof Types.StructType,
+          "Cannot visit invalid Iceberg type: %s for Avro complex union type: %s", type, union);

Review Comment:
   How about aligning by the type? `field_i` of type `x` aligns to the option of type `x`, regardless of the order? Else, we can mandate that the struct is in the same order as the options order (and the types match), and throw an exception here if not. I think both require recursively visiting the types to check for equality, but should be doable. The latter is kind of implemented here already, but I guess it will fail when trying to match the children as opposed to failing when trying to match the union itself.



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