apache/seatunnel · error · java.lang.UnsupportedOperationException

Map type should be handled via FragmentConverter.writeMapToV

Error message

Map type should be handled via FragmentConverter.writeMapToVector

What it means

MapTypeWriter.writeToVector is deliberately unusable: MAP-typed columns in the Lance sink are not written through the generic per-column TypeWriter dispatch, but through the dedicated FragmentConverter.writeMapToVector code path. Hitting this throw means a map value was routed to the wrong writer path — an internal dispatch bug rather than a user data problem.

Source

Thrown at seatunnel-connectors-v2/connector-lance/src/main/java/org/apache/seatunnel/connectors/seatunnel/lance/sink/writers/MapTypeWriter.java:34

 */

package org.apache.seatunnel.connectors.seatunnel.lance.sink.writers;

import org.apache.arrow.memory.BufferAllocator;
import org.apache.arrow.vector.FieldVector;
import org.apache.arrow.vector.complex.impl.UnionListWriter;
import org.apache.arrow.vector.complex.impl.UnionMapWriter;
import org.apache.arrow.vector.types.pojo.ArrowType;

public class MapTypeWriter extends BaseTypeWriter {
    @Override
    public void writeToVector(
            FieldVector vector,
            ArrowType arrowType,
            Object value,
            int rowIndex,
            BufferAllocator allocator) {
        throw new UnsupportedOperationException(
                "Map type should be handled via FragmentConverter.writeMapToVector");
    }

    @Override
    public void writeToListWriter(
            UnionListWriter writer, ArrowType arrowType, Object value, BufferAllocator allocator) {
        throw new UnsupportedOperationException("Map in list writing not yet implemented");
    }

    @Override
    public void writeToMapKey(
            UnionMapWriter writer, ArrowType arrowType, Object value, BufferAllocator allocator) {
        throw new UnsupportedOperationException("Map as map key is not supported");
    }

    @Override
    public void writeToMapValue(
            UnionMapWriter writer, ArrowType arrowType, Object value, BufferAllocator allocator) {

View on GitHub (pinned to cf67b549a7)

Solutions

Inspect FragmentConverter.setVectorValue and ensure ArrowType.Map is checked BEFORE the generic TypeWriterFactory.getWriter dispatch so writeMapToVector is used.
If you added a new write path, route Map-typed fields explicitly to FragmentConverter.writeMapToVector.
File/verify a connector bug with the schema (field type map<...>) that triggered the wrong dispatch.
As a workaround, convert the MAP column to a JSON string in the pipeline until the dispatch is fixed.

Example fix

// before (generic dispatch)
TypeWriter writer = TypeWriterFactory.getWriter(field.getType());
writer.writeToVector(vector, field.getType(), value, rowIndex, allocator);

// after (special-case map)
if (field.getType() instanceof ArrowType.Map) {
    FragmentConverter.writeMapToVector(mapVector, field, value, rowIndex, allocator);
} else {
    TypeWriterFactory.getWriter(field.getType()).writeToVector(vector, field.getType(), value, rowIndex, allocator);
}

Defensive patterns

Strategy: try-catch

Validate before calling

// Java: ensure map fields are routed to the dedicated path
boolean mapHandledSpecially = field.getType() instanceof ArrowType.Map;
if (!mapHandledSpecially) { /* safe to use TypeWriterFactory */ }

Try / catch

try {
    writer.writeToVector(vector, arrowType, value, rowIndex, allocator);
} catch (UnsupportedOperationException e) {
    if (e.getMessage().contains("FragmentConverter.writeMapToVector")) {
        FragmentConverter.writeMapToVector((MapVector) vector, field, value, rowIndex, allocator);
    } else { throw e; }
}

Prevention

Never call the generic TypeWriter dispatch for ArrowType.Map fields
Keep the map special-case first in any dispatch code you add to FragmentConverter
Add a unit test covering a map column through setVectorValue

When it happens

Trigger: FragmentConverter.setVectorValue (or a custom caller) calls TypeWriterFactory.getWriter for an ArrowType.Map field and invokes writeToVector instead of special-casing it with writeMapToVector.

Common situations: Any Lance sink write containing a MAP column where the converter's type dispatch fails to recognize the Map arrow type first; modifications to FragmentConverter that bypass the map branch.

Understand the failure class

Background: "This is a bug, please report it": internal invariant violations, unreachable panics, and SNH errors explained — this error's family across 47 libraries.

Related errors

AI-assisted analysis of apache/seatunnel@cf67b549a7 (2026-09-10). Data as JSON: /api/errors/7b694f756371b85a. Report an issue: GitHub.