apache/pulsar · error · RuntimeException

Schema `${type}` is not supported to be used as a field for

Error message

Schema `${type}` is not supported to be used as a field for now

What it means

FieldSchemaBuilderImpl builds a schema for a single field of a struct (AVRO-based) schema. When the builder's schema type is neither AVRO/JSON/PROTO types handled above the switch, nor BOOLEAN/INT8..DOUBLE/STRING/BYTES/DATE/TIME/TIMESTAMP/LOCAL_* primitives, nor a generic Avro schema, the default branch throws a RuntimeException because only these types can currently be used as a field schema.

Source

Thrown at pulsar-client/src/main/java/org/apache/pulsar/client/impl/schema/FieldSchemaBuilderImpl.java:159

            case TIMESTAMP:
                baseSchema = LogicalTypes.timestampMillis().addToSchema(Schema.create(Schema.Type.LONG));
                break;
            case JSON:
                checkArgument(genericSchema.getSchemaInfo().getType() == SchemaType.JSON,
                        "The field is expected to be using JSON schema but "
                                + genericSchema.getSchemaInfo().getType() + " schema is found");
                AvroBaseStructSchema genericJsonSchema = (AvroBaseStructSchema) genericSchema;
                baseSchema = genericJsonSchema.getAvroSchema();
                break;
            case AVRO:
                checkArgument(genericSchema.getSchemaInfo().getType() == SchemaType.AVRO,
                        "The field is expected to be using AVRO schema but "
                                + genericSchema.getSchemaInfo().getType() + " schema is found");
                GenericAvroSchema genericAvroSchema = (GenericAvroSchema) genericSchema;
                baseSchema = genericAvroSchema.getAvroSchema();
                break;
            default:
                throw new RuntimeException("Schema `" + type + "` is not supported to be used as a field for now");
        }

        for (Map.Entry<String, String> entry : properties.entrySet()) {
            baseSchema.addProp(entry.getKey(), entry.getValue());
        }

        if (null != aliases) {
            for (String alias : aliases) {
                baseSchema.addAlias(alias);
            }
        }

        final Schema finalSchema;
        if (optional) {
            if (defaultVal != null) {
                finalSchema = SchemaBuilder.builder().unionOf()
                    .type(baseSchema)
                    .and()

View on GitHub (pinned to 820761864e)

Solutions

1. Use one of the supported field schema types (primitives like STRING/INT32/DOUBLE, or AVRO/JSON/Protobuf struct types, or GenericAvroSchema)
2. If you need a nested record, build it via SchemaBuilder.<T>.newRecordSchema()/aRecord() with an AVRO-compatible type instead of an unsupported SchemaType
3. Check SchemaType.isStructType / supported primitive list before invoking addField to fail fast with a clearer message

Example fix

// before
Schema schema = SchemaBuilder.aRecord().addField("f", FieldSchemaBuilder.of(SchemaType.NONE)).build();
// after
Schema schema = SchemaBuilder.aRecord().addField("f", FieldSchemaBuilder.of(SchemaType.STRING)).build();

static boolean isSupportedFieldType(SchemaType t) { return t == SchemaType.STRING || t == SchemaType.BOOLEAN || t == SchemaType.INT8 || t == SchemaType.INT16 || t == SchemaType.INT32 || t == SchemaType.INT64 || t == SchemaType.FLOAT || t == SchemaType.DOUBLE || t == SchemaType.BYTES || t == SchemaType.DATE || t == SchemaType.TIME || t == SchemaType.TIMESTAMP || SchemaType.isStructType(t); }
if (!isSupportedFieldType(type)) throw new IllegalArgumentException("Unsupported field schema type: " + type);

boolean isStructOrPrimitive(SchemaType t) { return SchemaType.isStructType(t) || t.isPrimitive(); }

try { fieldBuilder.build(); } catch (RuntimeException e) { if (e.getMessage().contains("not supported to be used as a field")) { /* fallback to supported type */ } else throw e; }

When it happens

Trigger: Calling SchemaBuilder.aRecord().addField(...) with a FieldSchemaBuilder whose type() was set to an unsupported SchemaType (e.g. NONE, KEY_VALUE, EXTERNAL, AUTO_CONSUME, AUTO_PUBLISH) and then invoking build().

Common situations: Dynamically building record schemas from user/config-supplied type names where an unknown or unsupported type string maps to a SchemaType that isn't field-compatible; copying schema types from a KeyValue schema into a field.

Related errors

• Error during schema compatibility check with strategy ${stra
• Retrieve schema instance from schema info for type '${schema
• The input schema is not of type 'org.apache.avro.Schema'.
• Currently only AVRO and JSON record schema is supported
• Avro Record Builder doesn't support non-avro record as a fie

AI-assisted analysis of apache/pulsar@820761864e (2026-09-06). Data as JSON: /api/errors/757f8574466c5265. Report an issue: GitHub.