mzabaluev opened a new issue, #9608:
URL: https://github.com/apache/arrow-rs/issues/9608
**Describe the bug**
An application that needs to count records in an Avro file without decoding
any fields may pass a reader schema to that effect.
In the current implementation, `RecordDecoder` creates a `RecordBatch` from
decoded column arrays without the `row_count` option, which results in an error
when there are no columns to decide the number of rows from.
**To Reproduce**
Create an arrow-avro reader with a reader schema matching the top-level
record of the Avro content (e.g. an OCF file) schema, but listing no fields,
e.g.
```json
{
"type": "record",
"name": "topLevelRecord",
"fields": []
}
```
Use the appropriate read API to read batches from the file.
The error is reported: "Invalid argument error: must either specify a row
count or at least one column"
**Expected behavior**
The reader retrieves batches with no columns, but numbers of rows as decided
by the batch size option and other flags affecting batch composition (i.e. the
row counts should be the same as if the full writer schema was read).
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