apache/seatunnel · error · RuntimeException

Failed to convert row to JSON

Error message

Failed to convert row to JSON

What it means

convertRowToJson serializes a SeaTunnelRow into a JSON string (used for JSON-based writes). Any exception during field mapping or Jackson serialization is rethrown as a RuntimeException with this message, chaining the original cause. It signals a row that cannot be represented as the expected JSON document.

Source

Thrown at seatunnel-connectors-v2/connector-databend/src/main/java/org/apache/seatunnel/connectors/seatunnel/databend/sink/DatabendSinkWriter.java:523

                    jsonNode.put(fieldName, (Double) value);
                } else if (value instanceof Boolean) {
                    jsonNode.put(fieldName, (Boolean) value);
                } else if (value instanceof BigDecimal) {
                    jsonNode.put(fieldName, (BigDecimal) value);
                } else if (value instanceof java.sql.Timestamp) {
                    jsonNode.put(fieldName, value.toString());
                } else if (value instanceof java.sql.Date) {
                    jsonNode.put(fieldName, value.toString());
                } else if (value instanceof byte[]) {
                    jsonNode.put(fieldName, Base64.getEncoder().encodeToString((byte[]) value));
                } else {
                    jsonNode.put(fieldName, value.toString());
                }
            }

            return objectMapper.writeValueAsString(jsonNode);
        } catch (Exception e) {
            throw new RuntimeException("Failed to convert row to JSON", e);
        }
    }

    private void initializePreparedStatement(SeaTunnelRow row) throws SQLException {
        log.info("Initializing PreparedStatement based on row data");

        // use sinkTablePath to get Schema
        String database = sinkTablePath.getDatabaseName();
        String table = sinkTablePath.getTableName();

        log.info("Querying target table schema for {}.{}", database, table);
        SeaTunnelRowType actualTableSchema = queryTableSchema(database, table);

        if (actualTableSchema != null) {
            log.info("Using actual table schema: {}", actualTableSchema);
            this.insertSql = generateInsertSql(database, table, actualTableSchema);
        } else {
            log.warn("Could not query table schema, using inferred schema from data");

View on GitHub (pinned to cf67b549a7)

Solutions

1. Read the chained cause ('Caused by') to see the exact serialization failure.
2. Check for unsupported SeaTunnel types in the row and map them to JSON-compatible types with an upstream transform.
3. Verify the catalog table metadata is loaded correctly so field names align with row fields.
4. Cast/normalize special columns (binary, complex types) before the Databend sink.

Example fix

// before: raw binary field reaches JSON conversion
row.setField(2, bytes);
// after: encode binary before sinking
row.setField(2, Base64.getEncoder().encodeToString(bytes));

// ensure every field is JSON-safe before sinking
for (int i = 0; i < row.getArity(); i++) {
    Object v = row.getField(i);
    if (v instanceof byte[] || v instanceof Map || v instanceof List) {
        // normalize before write
    }
}

boolean isJsonSerializable(Object v) {
    return v == null || v instanceof String || v instanceof Number
        || v instanceof Boolean || v instanceof java.time.temporal.Temporal;
}

try {
    writer.write(row);
} catch (RuntimeException e) {
    if ("Failed to convert row to JSON".equals(e.getMessage())) {
        log.error("JSON conversion failed; offending row types: "
            + Arrays.toString(row.getRowType().getFieldTypes()), e.getCause());
    } else throw e;
}

When it happens

Trigger: objectMapper.writeValueAsString throws (unsupported value types, Jackson config issue), or row fields contain objects that fail toString/field mapping; also triggered when the row shape does not match the expected catalog metadata during field iteration.

Common situations: Binary/special types (e.g. byte arrays, nested arrays) that Jackson cannot map by default; schema drift so row fields no longer match declared catalog columns; null catalog metadata causing wrong field-name lookups; corrupt values from upstream CDC sources.

Understand the failure class

Background: "JSON serialization failed", "not JSON serializable", "Failed to serialize": why JSON marshaling errors happen and how to fix them — this error's family across 46 libraries.

Related errors

• CONNECT_FAILED
• SQL_OPERATION_FAILED
• JSON_OPERATION_FAILED
• UNSUPPORTED_DATA_TYPE
• UNSUPPORTED_DATA_TYPE

AI-assisted analysis of apache/seatunnel@cf67b549a7 (2026-09-10). Data as JSON: /api/errors/a6f93ba9cfa773c9. Report an issue: GitHub.