[GitHub] [iceberg] rdblue commented on a change in pull request #3954: rewriting the operation when removing and adding the same partition col with the same transformation

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

rdblue commented on a change in pull request #3954:
URL: https://github.com/apache/iceberg/pull/3954#discussion_r790354893



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File path: core/src/main/java/org/apache/iceberg/BaseUpdatePartitionSpec.java
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@@ -124,6 +124,17 @@ public BaseUpdatePartitionSpec addField(Term term) {
     return addField(null, term);
   }
 
+  private BaseUpdatePartitionSpec rewriteDeleteAndAddField(
+      PartitionField existing, String name, Pair<Integer, Transform<?, ?>> sourceTransform) {
+    deletes.remove(existing.fieldId());
+    if (existing.name().equals(name)) {
+      return this;
+    } else {
+      String newName = name == null ? sourceTransform.second().toString() : name;
+      return renameField(existing.name(), newName);

Review comment:
       This uses the transform's string representation as the partition field name, but that's not how we generate partition field names. In fact, the result is that we have a partition field name for bucket transforms that is invalid or must be quoted in most systems (`"bucket[16]"`).
   
   Rather than generating the name, I think that this should consider a `null` name a no-op. That is if I remove `shard` and add `bucket(16, id)` then the result should still be named shard -- there's no reason to drop the name and we avoid breaking metadata tables needlessly.
   
   However, if the name was explicitly set, then drop and and should act as a rename.
   
   In short, I think it should be this:
   
   ```java
   if (name == null || existing.name().equals(name)) {
     return this;
   } else {
     return renameField(existing.name(), name);
   }
   ```




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