[I] Zero-column RecordBatch loses numRows after IPC deserialization [arrow-js]

["rustyconover (via GitHub)" <gi...@apache.org>]

rustyconover opened a new issue, #401:
URL: https://github.com/apache/arrow-js/issues/401

   `RecordBatch.numRows` returns 0 for zero-column batches deserialized from IPC, even when the IPC message header specifies a non-zero length. Zero-column RecordBatches are valid Arrow payloads and should preserve their row count through serialization round-trips.
   
   ## Current behavior
   
   1. An IPC stream contains a zero-column RecordBatch with `length: 100`
   2. The IPC reader correctly passes `header.length` to `makeData`, and `visitStruct` preserves it
   3. But `new RecordBatch(schema, data)` calls `ensureSameLengthData` which recomputes length as `chunks.reduce((max, col) => Math.max(max, col.length), 0)` — with zero children, this returns 0
   
   ## Expected behavior
   
   `RecordBatch.numRows` should be 100 after deserializing a zero-column batch with `length: 100`.
   
   ## Reproducer
   
   ```typescript
   import { makeData, RecordBatch, Schema, Struct } from 'apache-arrow';
   
   const schema = new Schema([]);
   const data = makeData({ type: new Struct([]), length: 100, nullCount: 0, children: [] });
   const batch = new RecordBatch(schema, data);
   
   console.log(batch.numRows); // 0 — expected 100
   ```
   
   ## Root cause
   
   In `src/recordbatch.ts` line 84, the 2-arg constructor path calls:
   
   ```typescript
   [this.schema, this.data] = ensureSameLengthData<T>(this.schema, this.data.children as Data<T[keyof T]>[]);
   ```
   
   `ensureSameLengthData` (line 323) defaults `maxLength` to `chunks.reduce(...)`, which returns 0 for an empty array.
   
   The 1-arg constructor path (line 102) already passes `length` explicitly and does not have this bug.
   
   ## Fix
   
   Pass `this.data.length` as the third argument to `ensureSameLengthData`, which already accepts an optional `maxLength` parameter.


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Re: [I] Zero-column RecordBatch loses numRows after IPC deserialization [arrow-js]

["kou (via GitHub)" <gi...@apache.org>]

kou closed issue #401: Zero-column RecordBatch loses numRows after IPC deserialization
URL: https://github.com/apache/arrow-js/issues/401


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