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Here is my revised code from my other review question Node JS delete multiple MySQL linked records and delete physical file

Just would like to hear some reviews if I have the right logic.

router.delete('/:id', (req, res)=>{


  function deleteCommentRecords(){
    db.beginTransaction(function(err) {
      if(err) return res.status(500).end(err.message);
      //Delete comment section records
      db.query("DELETE FROM commentSchema WHERE PostID = ?", req.params.id, (err, result)=>{
        if(err){
          db.rollback(()=>{
            return res.status(500).end(err.message);
          });
        }
        db.commit((err)=>{
          if(err){
            db.rollback(()=>{
              return res.status(500).end(err.message);
            });
          }
          console.log('Transaction Completed Successfully.');
        });
      });
    });
  }


  function deletePostSchemaReords(){
    // Delete PostSchema records
    db.query("delete from postschema where id = ?", req.params.id, (err, result)=>{
      if(err) {
        db.rollback(()=>{
          return res.status(500).end(err.message);
        });
      }
      db.commit((err)=>{
        if(err){
          db.rollback(()=>{
            return res.status(500).end(err.message);
          });
        }
        console.log('Transaction Completed Successfully.');
      });
    });
  }

  function loadData(){

    // Get filenames from Comments
    db.query("SELECT image FROM commentschema WHERE postID = ?", req.params.id, (error, comments_image_output)=>{
      if(error) return res.status(500).end(err.message);

      // If there is an image
      if(comments_image_output.length > 0){
        // Foreach image, delete one by one
        comments_image_output.forEach(function(row){
          try {
            console.log(row.image);
            fs.unlinkSync(uploadDir + row.image);
            console.log('Successfully deleted');
            // Query to remove commentSchema records
            deleteCommentRecords();
          } catch (err) {
          // handle the error
          }
        });
        // Redirect back to posts
        res.redirect(303, '/admin/posts');
      }
        deleteCommentRecords();
    })


    // Get filename from PostSchema
    db.query("SELECT filename FROM PostSchema WHERE id = ?", req.params.id, (err,post_image_output)=>{
      if(err) return res.status(500).end(err.message);
      if(post_image_output.length > 0){
        // Foreach image, delete one by one
        post_image_output.forEach(function(row){
          try {
            console.log(row.filename);
            fs.unlinkSync(uploadDir + row.filename);
            console.log('Successfully deleted files');
            deletePostSchemaReords();
          } catch (err) {
          // handle the error
          }
        });
      }
        deletePostSchemaReords();
    });
  }
  loadData();
});
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There are some problems with this implementation:

  • if both the query in loadData fail, res.status(500).end(err.message) is run twice so you will get an error RESPONSE ALREADY CLOSED that could lead to server crash, and this must be avoided
  • you are not using a linter on your code. I can say that because you have the error parameter in the callback, but in the code, you wrote ..end(err.message), so adopt a linter to see these error before they happen in production that would cause a crash of your application since err would be undefined
  • every request adds in the memory heap the functions loadData, deletePostSchemaReords and deleteCommentRecords causing pressure on the garbage collector and slowing down your endpoints and this can be voided
  • a lot of code replicated that must be avoided to have a nice and maintainable endpoint
  • fs.unlinkSync kills the performance in an API endpoint
  • deleteCommentRecords() is called for every comments_image_output but this would execute comments_image_output.length times the same query, this is a functional error
  • in deleteCommentRecords() a transaction begins and the immediately committed so it is not adding any performance gain: a transaction works best when there are multiple query to execute across multiple tables
  • the loadData function is deleting rows from DB, so the name is misbehaviour
  • in deletePostSchemaReords there is only a query without the transaction so the rollback is ineffective
  • the response object should be managed by one entity otherwise there is too much coupling between general functions (like delete an array of files) and the HTTP protocol

Here how I would proceed with the refactor.

  • I used the callback style (instead of async/await) since you are not using promises
  • I assume there is a db and a uploadDir global objects - since are not in the code example
router.delete('/:id', (req, res) => {
  loadData(req.params.id, (err, files) => {
    if (err) { return res.status(500).end(err.message) }

    // if both query are successful delete from the database
    deleteAll(req.params.id, (err) => {
      if (err) { return res.status(500).end(err.message) }

      res.redirect(303, '/admin/posts') // response to the client first

      // the database deletion is OK, now delete the files quitely
      const deleteFileArray = files.comment.concat(files.post)
      deleteFiles(deleteFileArray, (err) => {
        if (err) {
          console.log('ops failed to delete files, but who cares?')
        }
      })
    })
  })
})

function loadData (postId, callback) {
  let runs = 0
  const output = { comment: null, post: null, error: null }

  db.query('SELECT image FROM commentschema WHERE postID = ?', postId, processQueryResult.bind(null, 'comment', 'image'))
  db.query('SELECT filename FROM PostSchema WHERE id = ?', postId, processQueryResult.bind(null, 'post', 'filename'))

  // this function will be executed twice an manage only one callback call
  function processQueryResult (responseType, columnName, error, images) {
    if (error) {
      output.error = error
    } else {
      output[responseType] = images.map(row => uploadDir + row[columnName])
    }

    if (++runs === 2) { // call the callback with the sum of the files to delete
      callback(output.error, output)
    }
  }
}

function deleteAll (postId, callback) {
  // Delete PostSchema records
  db.beginTransaction(function (err) {
    if (err) return callback(err)

    // Delete comment section records
    db.query('DELETE FROM commentSchema WHERE PostID = ?', postId, (err) => {
      if (err) { return db.rollback(callback.bind(null, err)) }

      db.query('DELETE FROM postschema where id = ?', postId, (err) => {
        if (err) { return db.rollback(callback.bind(null, err)) }

        db.commit((err) => {
          if (err) { return db.rollback(callback.bind(null, err)) }
          console.log('Transaction Completed Successfully.')
          callback()
        })
      })
    })
  })
}

function deleteFiles (files, callback) {
  let i = files.length
  files.map(function (filepath) {
    fs.unlink(filepath, function (err) {
      if (err) {
        callback(err)
      } else if (--i <= 0) {
        callback(null)
      }
    })
  })
}
```
| improve this answer | |
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  • \$\begingroup\$ Just realized - If there is a comment without an image (Because people can comment without attaching an image). It throws console.log('ops failed to delete files, but who cares?') \$\endgroup\$ – LV98 Aug 21 at 18:32
  • \$\begingroup\$ You need only to change the query to avoid selection of the post without images, you will reduce the payload of the query and all will works as expected \$\endgroup\$ – Manuel Spigolon Aug 21 at 19:14

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