apache/beam · error · IllegalArgumentException

Cannot infer types from

Error message

Cannot infer types from %s. This is currently unsupported, use List instead of Array.

What it means

CalciteUtils.sqlTypeWithAutoCast infers a Calcite RelDataType from a Java reflection Type for UDF/UDAF argument resolution. Java GenericArrayType (i.e. T[] parameters) is not supported, so IllegalArgumentException tells you to use java.util.List instead of raw arrays. Beam SQL maps List<E> to ARRAY and Map<K,V> to MAP, but not array-typed signatures.

Solutions

1. Change the UDF signature to use java.util.List (e.g. List<String>) instead of String[].
2. Wrap array values into a List before returning them from the UDF.
3. Adjust the SQL call site to pass ARRAY literals, which map to List on the Java side.

Example fix

// before
public String[] splitNames(String input) { ... }
// after
public List<String> splitNames(String input) { ... }

for (Type p : method.getGenericParameterTypes()) {
  if (p instanceof GenericArrayType) throw new IllegalArgumentException("Use List instead of arrays in UDF signature");
}

boolean usesArrays(Type t) { return t instanceof GenericArrayType || (t instanceof Class<?> c && c.isArray()); }

try { relType = CalciteUtils.sqlTypeWithAutoCast(typeFactory, type); }
catch (IllegalArgumentException e) { /* reject UDF or rewrite signature before registration */ }

When it happens

Trigger: Declaring a UDF method with an array parameter or return type (e.g. String[] or int[]) and invoking it through Beam SQL; the reflection-based type inference hits the `instanceof GenericArrayType` branch.

Common situations: Migrating plain Java UDFs that use arrays into Beam SQL UDFs; copying scalar UDF code from other SQL engines that allow array parameters.

Understand the failure class

Background: "is not a compatible type" / "cannot merge" errors: when a value's type doesn't match what the library requires — this error's family across 65 libraries.

Related errors

• Cannot create UDF from method: method
• Method is not public.
• must not throw checked exception
• No method annotated with @
• Cannot find a matching Beam FieldType for Calcite type:

AI-assisted analysis of apache/beam@12126d8942 (2026-09-13). Data as JSON: /api/errors/6cc7bbb76bd32c52. Report an issue: GitHub.

Appendix: source

Thrown at sdks/java/extensions/sql/src/main/java/org/apache/beam/sdk/extensions/sql/impl/utils/CalciteUtils.java:420

    if (type instanceof Class && AbstractInstant.class.isAssignableFrom((Class<?>) type)) {
      return typeFactory.createJavaType(Date.class);
    } else if (type instanceof Class && ByteString.class.isAssignableFrom((Class<?>) type)) {
      return typeFactory.createJavaType(byte[].class);
    } else if (type instanceof ParameterizedType) {
      ParameterizedType parameterizedType = (ParameterizedType) type;
      if (java.util.List.class.isAssignableFrom((Class<?>) parameterizedType.getRawType())) {
        RelDataType elementType =
            sqlTypeWithAutoCast(typeFactory, parameterizedType.getActualTypeArguments()[0]);
        return typeFactory.createArrayType(elementType, UNLIMITED_ARRAY_SIZE);
      } else if (java.util.Map.class.isAssignableFrom((Class<?>) parameterizedType.getRawType())) {
        RelDataType mapElementKeyType =
            sqlTypeWithAutoCast(typeFactory, parameterizedType.getActualTypeArguments()[0]);
        RelDataType mapElementValueType =
            sqlTypeWithAutoCast(typeFactory, parameterizedType.getActualTypeArguments()[1]);
        return typeFactory.createMapType(mapElementKeyType, mapElementValueType);
      }
    } else if (type instanceof GenericArrayType) {
      throw new IllegalArgumentException(
          "Cannot infer types from "
              + type
              + ". This is currently unsupported, use List instead "
              + "of Array.");
    }
    if (type instanceof Class) {
      Class<?> clazz = (Class<?>) type;
      SqlTypeName sqlTypeName = JAVA_TO_SQL_TYPE_MAPPING.get(clazz);
      if (sqlTypeName != null) {
        return typeFactory.createTypeWithNullability(
            typeFactory.createSqlType(sqlTypeName), !clazz.isPrimitive());
      }
    }
    return typeFactory.createJavaType((Class) type);
  }
}

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