apache/seatunnel · error · MongodbConnectorException

UNSUPPORTED_OPERATION

UNSUPPORTED_OPERATION

Error message

Bson format doesn't support non-string as key type of map. The type is: ${typeSummary}

What it means

createMapConverter validates that the MAP key type is STRING before building the converter. BSON object keys are always strings, so a MapType with a non-string key (INT, BIGINT, etc.) cannot round-trip through BSON, and the converter construction fails with MongodbConnectorException(UNSUPPORTED_OPERATION).

Source

Thrown at seatunnel-connectors-v2/connector-mongodb/src/main/java/org/apache/seatunnel/connectors/seatunnel/mongodb/serde/BsonToRowDataConverters.java:311

                                    + bsonValue
                                    + "' of type "
                                    + bsonValue.getBsonType());
                }

                List<BsonValue> in = bsonValue.asArray();
                Object arr = Array.newInstance(type.getElementType().getTypeClass(), in.size());
                for (int i = 0; i < in.size(); i++) {
                    Array.set(arr, i, elementConverter.apply(in.get(i)));
                }
                return arr;
            }
        };
    }

    private static SerializableFunction<BsonValue, Object> createMapConverter(
            String typeSummary, SeaTunnelDataType<?> keyType, SeaTunnelDataType<?> valueType) {
        if (!keyType.getSqlType().equals(SqlType.STRING)) {
            throw new MongodbConnectorException(
                    UNSUPPORTED_OPERATION,
                    "Bson format doesn't support non-string as key type of map. The type is: "
                            + typeSummary);
        }
        SerializableFunction<BsonValue, Object> valueConverter =
                createNullSafeInternalConverter(valueType);

        return new SerializableFunction<BsonValue, Object>() {
            private static final long serialVersionUID = 1L;

            @Override
            public Object apply(BsonValue bsonValue) {
                if (!bsonValue.isDocument()) {
                    throw new MongodbConnectorException(
                            ILLEGAL_ARGUMENT,
                            "Unable to convert to rowType from unexpected value '"
                                    + bsonValue
                                    + "' of type "

View on GitHub (pinned to cf67b549a7)

Solutions

Change the map key type to STRING in the schema definition.
Use a ROW or ARRAY<ROW<k,v>> structure to represent non-string-keyed data.
Store the map with string keys in MongoDB (e.g. keys as strings) and convert keys downstream.
If you own the code, extend createMapConverter to coerce numeric keys to strings during deserialization.

Example fix

// before
scores = MAP<INT, DOUBLE>
// after
scores = MAP<STRING, DOUBLE>

Defensive patterns

Strategy: validation

Validate before calling

// Validate map key type before building the schema
if (mapType.getKeyType().getSqlType() != SqlType.STRING) {
    throw new IllegalArgumentException(
        "MongoDB connector requires MAP keys to be STRING, got: " + mapType.getKeyType());
}

Try / catch

try {
    buildSchema(options);
} catch (MongodbConnectorException e) {
    if (e.getMessage().contains("non-string as key type of map")) {
        // switch the map key type to STRING or restructure as ARRAY<ROW<k,v>>
    } else { throw e; }
}

Prevention

Always declare MAP<STRING, V> for MongoDB sources
Model non-string-keyed data as ROW or ARRAY<ROW<k,v>> instead of MAP
Remember BSON object keys are always strings; match your schema to that constraint

When it happens

Trigger: Declaring a MAP<INT, V>, MAP<BIGINT, V>, or any non-STRING key type in the SeaTunnel schema for a MongoDB source; createInternalConverter -> createMapConverter raises at converter-build time.

Common situations: Reusing a schema from another connector (e.g. JDBC) where integer-keyed maps are fine; auto-generated schemas mapping Mongo fields to MAP with inferred non-string keys.

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

AI-assisted analysis of apache/seatunnel@cf67b549a7 (2026-09-10). Data as JSON: /api/errors/d07f149b3fb35fd9. Report an issue: GitHub.