go-train-delay-ml-pipeline-data-extract

go-train-delay-ml-pipeline-data-extract.rs

async fn extract(&self) -> Result<String, AppError> {
  let stmt = &self
            .client
            .prepare("COPY (SELECT * From delays) TO STDOUT (FORMAT CSV, HEADER TRUE, quote ' ')")
            .await?;

  let data = self
            .client
            .copy_out(stmt)
            .await?
            .try_fold(BytesMut::new(), |mut buf, chunk| async move {
                buf.extend_from_slice(&chunk);
                Ok(buf)
            })
            .await?;

  let file_name = format!(
            "./data/{}.csv",
            chrono::offset::Utc::now().date().to_string()
  );

  let mut writer = csv::WriterBuilder::new()
            .quote_style(csv::QuoteStyle::Never)
            .from_path(file_name.clone())?;

  writer.write_field(data)?;

  writer.flush()?;
        Ok(file_name)
}