HuaHuaY opened a new issue, #47664:
URL: https://github.com/apache/arrow/issues/47664
### Describe the bug, including details regarding any error messages,
version, and platform.
`nums_rows()` method is inherited from `ParquetFileWriter`. It seems that
the method is designed to count the number of rows of RowGroups which are
closed.
```cpp
/// Number of rows in the yet started RowGroups.
///
/// Changes on the addition of a new RowGroup.
int64_t num_rows() const;
```
But in the implementation of `class FileSerializer : public
ParquetFileWriter::Contents`, the `num_rows_` variable is only modified in
`Close` method. It means that `num_rows()` method always returns `0` before
`Close` is called.
And after `Close` of `ParquetFileWriter` is called we can no longer call
`nums_rows()` method, because `contents_` is reset in `Close` and we will get a
null pointer exception if we call `nums_rows()`.
So, in the current implementation of `FileSerializer`, `num_rows()` will
only return `0` or throw exception.
```cpp
int ParquetFileWriter::num_columns() const { return
contents_->num_columns(); }
void ParquetFileWriter::Close() {
if (contents_) {
contents_->Close();
file_metadata_ = contents_->metadata();
contents_.reset();
}
}
// The following is the code of `FileSerializer`.
int64_t num_rows() const override { return num_rows_; }
void Close() override {
if (is_open_) {
if (row_group_writer_) {
num_rows_ += row_group_writer_->num_rows(); // <- num_rows is
only modified here and can never be read.
...
}
...
}
RowGroupWriter* AppendRowGroup(bool buffered_row_group) {
if (row_group_writer_) {
// <- A possible missing `num_rows_ += row_group_writer_->num_rows()`
here.
row_group_writer_->Close();
}
...
}
```
Should we mark the virtual method in `ParquetFileWriter` deprecated and
remove the method in next release? I guess the method which is used to count
the row number during writing row groups is useless and our default
implementation always returns 0 now. Otherwise we can fix the issue by
following the comments above.
### Component(s)
C++
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