apache/beam · error · java.lang.RuntimeException

Could not determine a schema for type

Error message

Could not determine a schema for type 

What it means

For an array parameter whose component type is not primitive/wrapper/String, the service tries to resolve a Row schema for the component type to validate payload rows; when getParameterSchema returns null (no valid schema), this error is thrown naming the component class.

Solutions

1. Register a schema for the array's component class (@DefaultSchema / SchemaProvider) and redeploy.
2. Use a schema-supported component type (POJO with fields, AVRO, Row).
3. Verify the expansion service classpath includes the compiled class with schema field registration for the component type.

Example fix

// before
public MyTransform withItems(Item[] items) {...}  // Item has no schema
// after
@DefaultSchema(JavaFieldSchema.class)
class Item { public final String id; public Item(String id){this.id=id;} }

Class<?> comp = paramClass.getComponentType();
try {
  Schema s = SchemaRegistry.getDefault().getSchema(comp);
  if (s == null || s.getFieldCount() == 0) throw new IllegalStateException("Register a schema for array component " + comp);
} catch (NoSuchSchemaException e) { throw new IllegalStateException("No schema for " + comp, e); }

try {
  return getTransform(payload);
} catch (RuntimeException e) {
  if (e.getMessage() != null && e.getMessage().startsWith("Could not determine a schema for type")) {
    throw new InvalidExpansionRequest("Array component type lacks schema: " + paramClass, e);
  }
  throw e;
}

When it happens

Trigger: Array parameter of POJO/complex component type whose component class has no registered, non-empty schema in the SchemaRegistry at expansion time.

Common situations: Complex-typed arrays (custom classes) in builder methods where the component class lacks @DefaultSchema registration; stale artifact deployed to the expansion service missing schema metadata.

Understand the failure class

Background: Schema validation failed / invalid input schema: payload rejected because its shape doesn't match the expected schema — this error's family across 28 libraries.

Related errors

• Could not find a matching method in transform for…
• Expected a schema with a single array field but received
• is not nullable in Array field
• Arrow schema conversion does not support Beam type
• Builder method has to be explicitly allowed

AI-assisted analysis of apache/beam@12126d8942 (2026-09-13). Data as JSON: /api/errors/73eeca9f67e5bbeb. Report an issue: GitHub.

Appendix: source

Thrown at sdks/java/expansion-service/src/main/java/org/apache/beam/sdk/expansion/service/JavaClassLookupTransformProvider.java:310

      }

      // We perform additional validation for arrays and non-primitive types.
      if (parameterClass.isArray()) {
        Class<?> arrayFieldClass = parameterClass.getComponentType();
        if (parameterFromPayload.getType().getTypeName() != TypeName.ARRAY) {
          throw new RuntimeException(
              "Expected a schema with a single array field but received "
                  + parameterFromPayload.getType().getTypeName());
        }

        // Following is a best-effort validation that may not cover all cases. Idea is to resolve
        // ambiguities as much as possible to determine an exact match for the given set of
        // parameters. If there are ambiguities, the expansion will fail.
        if (!isPrimitiveOrWrapperOrString(arrayFieldClass)) {
          @Nullable Collection<Row> values = constructorRow.getArray(i);
          Schema arrayFieldSchema = getParameterSchema(arrayFieldClass);
          if (arrayFieldSchema == null) {
            throw new RuntimeException("Could not determine a schema for type " + arrayFieldClass);
          }
          if (values != null) {
            @Nullable Row firstItem = values.iterator().next();
            if (firstItem != null && !firstItem.getSchema().assignableTo(arrayFieldSchema)) {
              return false;
            }
          }
        }
      } else if (constructorRow.getValue(i) instanceof Row) {
        @Nullable Row parameterRow = constructorRow.getRow(i);
        Schema schema = getParameterSchema(parameterClass);
        if (schema == null) {
          throw new RuntimeException("Could not determine a schema for type " + parameterClass);
        }
        if (parameterRow != null && !parameterRow.getSchema().assignableTo(schema)) {
          return false;
        }
      }

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