apache/iceberg · error · UnsupportedOperationException

Cannot update InternalRecordWrapper

Error message

Cannot update InternalRecordWrapper

What it means

InternalRecordWrapper is a read-only StructLike view over another record/wrapper. Its set(int pos, T value) mutator is intentionally unsupported because the wrapper delegates reads but never owns mutable storage. Attempting to write through the wrapper throws UnsupportedOperationException.

Source

Thrown at data/src/main/java/org/apache/iceberg/data/InternalRecordWrapper.java:112

  }

  @Override
  public <T> T get(int pos, Class<T> javaClass) {
    if (transforms[pos] != null) {
      Object value = wrapped.get(pos, Object.class);
      if (value == null) {
        // transforms function don't allow to handle null values, so just return null here.
        return null;
      } else {
        return javaClass.cast(transforms[pos].apply(value));
      }
    }
    return wrapped.get(pos, javaClass);
  }

  @Override
  public <T> void set(int pos, T value) {
    throw new UnsupportedOperationException("Cannot update InternalRecordWrapper");
  }
}

View on GitHub (pinned to 86d9c8fc54)

Solutions

1. Unwrap and mutate the underlying record instead of the wrapper (access the wrapped object).
2. Build a new record with the desired values rather than writing through the wrapper.
3. Use a mutable StructLike (e.g. Record from GenericRecord or InternalRecord) as the write target.
4. Restructure code so wrappers are used only on the read/projection side.

Example fix

// before
wrapper.set(2, newValue); // UnsupportedOperationException

// after
Record inner = (Record) Data.getDataFromType(wrapper.wrapped());
inner.set(2, newValue);

if (structLike instanceof InternalRecordWrapper) {
  throw new IllegalArgumentException("Wrapper is read-only; mutate the wrapped record instead");
}

StructLike writableTarget(StructLike s) {
  return (s instanceof InternalRecordWrapper)
      ? ((InternalRecordWrapper) s).wrapped() instanceof StructLike
          ? (StructLike) ((InternalRecordWrapper) s).wrapped()
          : null
      : s;
}

try {
  struct.set(pos, value);
} catch (UnsupportedOperationException e) {
  throw new IllegalStateException("Pass a mutable record, not an InternalRecordWrapper", e);
}

When it happens

Trigger: Calling set(pos, value) on an InternalRecordWrapper instance — e.g. code treating the wrapper as a writable StructLike when projecting, copying, or writing records through APIs that accept StructLike.

Common situations: Passing an InternalRecordWrapper to a writer or data-path that calls StructLike.set; reusing projection wrappers as output records; generic code that both reads and writes StructLike instances.

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

• Cannot set fields in a TypeProjection
• Not implemented: set
• Not implemented: set
• Not implemented: set
• Can't retrieve values from an empty struct

AI-assisted analysis of apache/iceberg@86d9c8fc54 (2026-09-12). Data as JSON: /api/errors/68869685b2e0bc51. Report an issue: GitHub.