apache/beam · error

bigqueryio.Read: type

Error message

bigqueryio.Read: type %v has no columns to select

What it means

bigqueryio.Read builds a SELECT statement from the struct's exported field names (via structx.InferFieldNames). If the type yields zero columns — e.g. an empty struct, an unexported-only struct, or a non-struct type — there is nothing to select, so the library panics.

Solutions

  1. Export the struct fields (capitalize) used as BigQuery columns.
  2. Add or fix struct tags matching tagKey so fields are recognized as columns.
  3. Use a non-empty struct type representing the table schema.

Example fix

// before
type row struct { name string } // unexported: no columns
beam.ParDo0(s, ..., ) ; bigqueryio.Read(s, project, "dataset", "table", reflect.TypeOf(row{}))
// after
type row struct { Name string `bigquery:"name"` }
Defensive patterns

Strategy: validation

Validate before calling

t := reflect.TypeOf(row{})
if t.Kind() != reflect.Struct || structx.InferFieldNames(t, "bigquery") == nil || len(structx.InferFieldNames(t, "bigquery")) == 0 {
    return errors.New("row type must have at least one exported/annotated column")
}

Type guard

func hasColumns(t reflect.Type) bool {
    return t.Kind() == reflect.Struct && t.NumField() > 0
}

Try / catch

func safeRead(s beam.Scope, proj, ds, tbl string, t reflect.Type) (pc beam.PCollection, err error) {
    defer func() {
        if r := recover(); r != nil {
            err = fmt.Errorf("bigqueryio.Read failed: %v", r)
        }
    }()
    return bigqueryio.Read(s, proj, ds, tbl, t), nil
}

Prevention

When it happens

Trigger: Calling bigqueryio.Read (or Query path) with a Go type t whose inferred column list is empty: struct with no exported fields, all fields ignored via the tag key, or a non-struct type.

Common situations: Defining a BigQuery row struct with only unexported fields, forgetting to export fields after a rename, or using a struct tag key that ignores all fields.

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

AI-assisted analysis of apache/beam@12126d8942 (2026-09-13). Data as JSON: /api/errors/581a31a2f7e9d92d. Report an issue: GitHub.

Appendix: source

Thrown at sdks/go/pkg/beam/io/bigqueryio/bigquery.go:105

// Read reads all rows from the given table. The table must have a schema
// compatible with the given type, t, and Read returns a PCollection<t>. If the
// table has more rows than t, then Read is implicitly a projection.
func Read(s beam.Scope, project, table string, t reflect.Type) beam.PCollection {
	mustParseTable(table)

	s = s.Scope("bigquery.Read")

	stmt := constructSelectStatement(t, bigQueryTag, table)

	return query(s, project, stmt, t)
}

func constructSelectStatement(t reflect.Type, tagKey string, table string) string {
	columns := structx.InferFieldNames(t, tagKey)

	if len(columns) == 0 {
		panic(fmt.Sprintf("bigqueryio.Read: type %v has no columns to select", t))
	}

	columnStr := strings.Join(columns, ", ")

	return fmt.Sprintf("SELECT %v FROM [%v]", columnStr, table)
}

// QueryOptions represents additional options for executing a query.
type QueryOptions struct {
	// UseStandardSQL enables BigQuery's Standard SQL dialect when executing a query.
	UseStandardSQL bool
	// Parameters are the query parameters for parameterized queries.
	// In the current implementation, user-defines types are not supported in Value field.
	// Use *bigquery.QueryParameterValue to build STRUCT/ARRAY parameters
	// or use go primitive types explicitly.
	parameters []bigquery.QueryParameter
}

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