apache/beam · error · ValueError

Columns are required with the table name.

Error message

Columns are required with the table name.

What it means

SpannerIO's read connector allows specifying just a table name for convenience, but a table read without a column list has no defined projection, so __init__ raises ValueError requiring columns whenever table is given (and no explicit read_operations were supplied).

Solutions

1. Provide the columns list alongside table: spannerio.Read(..., table='Users', columns=['id', 'name']).
2. Alternatively pass sql='SELECT * FROM Users' instead of table.
3. Or construct read_operations explicitly with ReadOperation.table(..., columns=[...]) and pass that.
4. Make columns a required pipeline option when the table option is set.

Example fix

// before
read = spannerio.Read(project_id, instance_id, database_id, table='Users')
// after
read = spannerio.Read(project_id, instance_id, database_id,
                     table='Users', columns=['id', 'name', 'email'])

if table is not None and not columns:
    raise ValueError('columns is required when reading by table name')

try:
    read = spannerio.Read(project_id, instance_id, database_id, table=table, columns=columns)
except ValueError as e:
    if 'Columns are required' in str(e):
        raise RuntimeError(f'Specify columns for table {table!r}') from e
    raise

When it happens

Trigger: Calling spannerio.Read(project_id, instance_id, database_id, table='Users') without columns, when read_operations is None; also passing table with sql or omitting columns in kwargs.

Common situations: Developers expect SELECT * semantics and pass only a table name; code refactors drop the columns list; config-driven pipelines read a table name from options but forget the columns option.

Understand the failure class

Background: "missing required argument" and "the following required arguments were not provided": what required-argument errors mean and how to fix them — this error's family across 20 libraries.

Related errors

• Spanner required read operation, sql or table with columns.
• A BigQuery table or a query must be specified
• A function must be provided to convert the input type into…
• A has been supplied to the model handler, but the required…
• artifact_location is not specified. Please specify the…

AI-assisted analysis of apache/beam@12126d8942 (2026-09-13). Data as JSON: /api/errors/b5b2eae9986ea7db. Report an issue: GitHub.

Appendix: source

Thrown at sdks/python/apache_beam/io/gcp/experimental/spannerio.py:755

    """
    self._configuration = _BeamSpannerConfiguration(
        project=project_id,
        instance=instance_id,
        database=database_id,
        table=table,
        query_name=query_name,
        credentials=credentials,
        pool=pool,
        snapshot_read_timestamp=read_timestamp,
        snapshot_exact_staleness=exact_staleness)

    self._read_operations = read_operations
    self._transaction = transaction

    if self._read_operations is None:
      if table is not None:
        if columns is None:
          raise ValueError("Columns are required with the table name.")
        self._read_operations = [
            ReadOperation.table(
                table=table, columns=columns, index=index, keyset=keyset)
        ]
      elif sql is not None:
        self._read_operations = [
            ReadOperation.query(
                sql=sql, params=params, param_types=param_types)
        ]

  def expand(self, pbegin):
    if self._read_operations is not None and isinstance(pbegin, PBegin):
      pcoll = pbegin.pipeline | Create(self._read_operations)
    elif not isinstance(pbegin, PBegin):
      if self._read_operations is not None:
        raise ValueError(
            "Read operation in the constructor only works with "
            "the root of the pipeline.")

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