I find myself in a rather unique situation that I haven't encountered before, and I'm struggling to find relevant information on how to handle it. So, I decided to seek advice here in hopes of sparking a productive discussion on the matter.
Currently, I am developing a Node.js/Express application that involves performing a series of database calls within different route handlers. To accomplish this, I am utilizing the node-sqlite3 module for making these database queries. Specifically, users are uploading files, which are then saved to the filesystem (with plans to move them to blob storage later) and used to generate XML files for various purposes. To name these files, I rely on the database ID to create routes like '/file/:id' for retrieving the file later and preventing any naming conflicts.
Since I am working with CoffeeScript, I encapsulate this functionality within a class structure, allowing me to access helper methods using 'this' or '@'. Previously, I was fetching the last inserted row ID using 'last_insert_rowid()' after an insertion, but I realized this approach exposes vulnerabilities to race conditions. Instead, the node-sqlite3 module conveniently stores the last inserted row ID in the 'this' object during its callback upon completing an INSERT operation (e.g., '(err) -> fileid = @.lastID'). Here is a simplified snippet of my code:
uploadFile: (fileData, cb) ->
@.openConnectionIfClosed()
@db.serialize =>
@db.run 'insert into thing (val=$val)', $val: 'some_val', (err) =>
if err
cb err
return
fileid = @.lastID
async.waterfall [
(async_cb) =>
@.saveFile fileid, async_cb
...
], (err) => cb err
@.closeConnection()
The challenge I am facing is balancing the need to retain the class's 'this' scope for accessing instance methods while also extracting the 'lastID' value from the default 'this' object returned by the database callback. Using fat arrows in the callback would grant access to my class methods, but it renders '@.lastID' as 'undefined'. What would be the most appropriate solution to tackle this issue? Whether in CoffeeScript or JavaScript, I believe one workaround could involve creating a context variable like 'ctxt = @' at the beginning of the method, although this may not be the ideal approach. Any thoughts?
EDIT: It is worth noting that renaming the file is not feasible since the ID is necessary to update the database. The sequence of operations carried out by 'async.waterfall' includes saving the file, generating an XML metadata file, saving it, and retroactively updating the file path in the database entry. While there might be ways to streamline these database calls without total isolation, further exploration is required.