[Bug]: Row.toString throws for an ITERABLE field that is not backed by a List

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Assessment

Difficulty
2/5
Estimated time
1-3 hours
Newbie friendliness
76/100
Issue type
Bug
Clarity
Clearly specified
Activity status
Quiet
Tech stack
java
Domain
backend

Research direction

Start in SchemaUtils.java at toPrettyFieldValueString and trace the call from Row#toString through SchemaUtils.toPrettyString. Run the reproducer from the issue and add regression coverage for an ITERABLE backed by a plain Iterable; done means Row#toString completes without throwing for that value.

Written by the indexing model from the issue text.

Description

java P3
What happened?

Row#toString throws for an ITERABLE field whose value is a plain Iterable:

Schema schema =
    Schema.builder().addStringField("k").addIterableField("vals", FieldType.STRING).build();
Iterable<String> bare = () -> Arrays.asList("p", "q").iterator();
Row.withSchema(schema).attachValues("k1", bare).toString();

java.lang.IllegalArgumentException: value type is 'class ...' for field type 'ITERABLE'
	at org.apache.beam.sdk.schemas.SchemaUtils.toPrettyFieldValueString(SchemaUtils.java:273)

toPrettyFieldValueString requires a List before iterating:

if (!(value instanceof List)) {
  throw new IllegalArgumentException(...);
}

An ITERABLE field declares an Iterable, so the guard is stricter than the type it is guarding. The branch below it only iterates and counts — both available from an Iterable once materialised.

Row#toString is SchemaUtils.toPrettyString(this), so one unusual field takes out logging and debugger output for every field beside it, which is a poor trade for a stricter check in a renderer.

Note on where the fix belongs

There is a reasonable position that a materialised Row should always hold a List for ARRAY/ITERABLE, and that a non-List arriving here means a producer is at fault. That may well be true and worth fixing separately — but the reproducer above uses only Schema.builder, Row.withSchema(...).attachValues(...) and toString(), so a value that is merely Iterable does reach the renderer through the public API, and a toString() that throws is hard to defend regardless of who produced the value.

Issue Priority

Priority: 3 (minor)

Issue Components
  • Component: Java SDK
Dominant language
Java
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Merged PRs (30d)
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