apache/beam · error · CannotProvideCoderException

Cannot provide coder for elements of Create: For their commo

Error message

Cannot provide coder for elements of Create: For their common class, no coder could be provided. Based on their values, they do not all default to the same Coder.

What it means

Create.of(...) infers a Coder for its elements by calling inferCoderFromObject for each element; if the inferred coders differ between elements, no single coder can encode the PCollection and the pipeline construction fails with CannotProvideCoderException. This happens because Beam cannot guess a consistent encoding when a common class has no registered coder and the element values imply different coders (e.g. mixed generic/Polymorphic values).

Source

Thrown at sdks/java/core/src/main/java/org/apache/beam/sdk/transforms/Create.java:996

    // If that fails, try to deduce a coder using the elements themselves
    return (Coder<T>) inferCoderFromObjects(coderRegistry, schemaRegistry, elems);
  }

  /**
   * Attempts to infer the {@link Coder} of the elements ensuring that the returned coder is
   * equivalent for all elements.
   */
  private static Coder<?> inferCoderFromObjects(
      CoderRegistry coderRegistry, SchemaRegistry schemaRegistry, Iterable<?> elems)
      throws CannotProvideCoderException {
    Optional<Coder<?>> coder = Optional.absent();
    for (Object elem : elems) {
      Coder<?> c = inferCoderFromObject(coderRegistry, schemaRegistry, elem);
      if (!coder.isPresent()) {
        coder = (Optional) Optional.of(c);
      } else if (!Objects.equals(c, coder.get())) {
        throw new CannotProvideCoderException(
            "Cannot provide coder for elements of "
                + Create.class.getSimpleName()
                + ":"
                + " For their common class, no coder could be provided."
                + " Based on their values, they do not all default to the same Coder.");
      }
    }
    if (coder.isPresent()) {
      return coder.get();
    }

    throw new CannotProvideCoderException(
        "Cannot provide coder for elements of "
            + Create.class.getSimpleName()
            + ":"
            + " For their common class, no coder could be provided."
            + " Based on their values, no coder could be inferred.");
  }

View on GitHub (pinned to 12126d8942)

Solutions

Supply the coder explicitly: Create.of(elems).withCoder(MyCoder.of())
Annotate the element class with @DefaultCoder(MyCoder.class) or register a coder via CoderRegistry.registerCoderForClass
Ensure all elements in Create.of infer the same coder (same concrete type, not raw generics/Object)
If elements are of an Avro/POJO/Proto type, make sure the schema/coder provider (e.g. AvroCoder via @DefaultSchema) is on the classpath and registered

Example fix

// before
PCollection<Object> p = pipeline.apply(Create.of(new Foo(), new Bar()));
// after
PCollection<Foo> p = pipeline.apply(Create.of(foo1, foo2).withCoder(FooCoder.of()));

Defensive patterns

Strategy: validation

Validate before calling

// Verify every element infers the same coder before Create.of
List<Coder<?>> coders = elems.stream()
    .map(e -> pipeline.getCoderRegistry().getCoder(e.getClass()))
    .distinct()
    .collect(Collectors.toList());
if (coders.size() != 1) {
  // supply an explicit coder via .withCoder(...)
}

Try / catch

try {
  pipeline.apply(Create.of(elems));
} catch (CannotProvideCoderException e) {
  pipeline.apply(Create.of(elems).withCoder(MyCoder.of()));
}

Prevention

Annotate custom element classes with @DefaultCoder
Never use raw generic or Object element types with Create.of
Register coders for shared domain classes in a common pipeline setup

When it happens

Trigger: Calling Create.of(e1, e2, ...) where inferCoderFromObject returns different Coder instances for different elements, or where no coder can be resolved for the shared runtime class of the elements.

Common situations: Creating a PCollection from heterogeneous values typed only as Object, raw generic types, or classes without a registered default coder (no DefaultCoder annotation, no Coder registered in the CoderRegistry).

Understand the failure class

Background: Type mismatch errors: IllegalArgumentException, TypeError and type guards across 150 open-source libraries — this error's family across 150 libraries.

Related errors

AI-assisted analysis of apache/beam@12126d8942 (2026-09-13). Data as JSON: /api/errors/a89e53de760053a0. Report an issue: GitHub.