apache/iceberg · error · UnsupportedOperationException

Not implemented: set

Error message

Not implemented: set

What it means

SparkStructLike wraps a Spark InternalRow to expose it as Iceberg's StructLike. Iceberg's StructLike contract includes a set() mutation method, but this wrapper is read-only, so calling set() throws UnsupportedOperationException. It exists only to read struct values out of Spark rows during scans.

Source

Thrown at spark/v4.1/spark/src/main/java/org/apache/iceberg/spark/SparkStructLike.java:52

  public SparkStructLike wrap(Row row) {
    this.wrapped = row;
    return this;
  }

  @Override
  public int size() {
    return type.fields().size();
  }

  @Override
  public <T> T get(int pos, Class<T> javaClass) {
    Types.NestedField field = type.fields().get(pos);
    return javaClass.cast(SparkValueConverter.convert(field.type(), wrapped.get(pos)));
  }

  @Override
  public <T> void set(int pos, T value) {
    throw new UnsupportedOperationException("Not implemented: set");
  }
}

View on GitHub (pinned to 86d9c8fc54)

Solutions

1. Do not mutate SparkStructLike; treat it as read-only and build a mutable StructLike (e.g. via a Record or a fixed StructLike implementation) when writes are needed
2. Copy the values out of the Spark row into your own mutable record before mutation
3. Check whether the API you are calling truly needs a mutable StructLike; read paths (comparators, readers) never call set()

Example fix

// before
structLike.set(0, newValue); // throws UnsupportedOperationException
// after
Record copy = GenericRecord.create(schema).copyFieldValues(...);
copy.setField("col", newValue);

if (structLike instanceof SparkStructLike) {
  throw new IllegalArgumentException("SparkStructLike is read-only; use a mutable record");
}

boolean isReadOnlyStructLike(StructLike s) { return s instanceof SparkStructLike; }

try { s.set(pos, value); } catch (UnsupportedOperationException e) { /* build a mutable copy instead */ }

When it happens

Trigger: Calling set(int pos, T value) on a SparkStructLike instance — e.g. passing it to code that assumes a mutable StructLike (such as writers or updaters) instead of read-only scan contexts.

Common situations: Piping an Iceberg-wrapped Spark row into a custom writer, updater, or copy routine that mutates StructLike fields; using SparkStructLike outside the read path it was designed for.

Understand the failure class

Background: UnsupportedOperationException and "is not supported" errors: when a library deliberately refuses a call — this error's family across 30 libraries.

Related errors

• Not implemented: set
• Cannot set fields in a TypeProjection
• Cannot update InternalRecordWrapper
• Not implemented: set
• Remove is not supported

AI-assisted analysis of apache/iceberg@86d9c8fc54 (2026-09-12). Data as JSON: /api/errors/4221589f4f4a1947. Report an issue: GitHub.