MongoDB and Mongoose - Creating custom, autoindexed secondary IDs? - node.js

Question

I initialize my DB in the usual way:
mongoose.connect(`mongodb://uname:pword#127.0.0.1:port/dbname?authSource=admin`, {useNewUrlParser: true, autoIndex: false});
And I have a Schema, something like:
var materialSchema = new Schema({
bookID: {type: String, required: true},
active: Boolean,
name: {type: String, required: true},
stockLength: {type: Number, required: true}
});
module.exports = mongoose.model('material', materialSchema);
When I create a new material and add it to the database, it is automatically assigned the usual _id - which is a behaviour I want to maintain. BUT, I'd also like for bookID to be a unique, auto-incrementing index. This is for physical shelf storage, and not for queries or anything like that.
I'd like for bookID to increment in the following way:
A-001
A-002
A-003
...
A-098
A-099
A-100
B-001
...
B-100
...
Z-001
...
Z-100
In case the pattern above isn't clear, the pattern starts at A-001 and ultimately ends at Z-100. Each letter goes from 001 through 100 before moving to the next letter. Each new collection entry is just the next ID in the pattern. It is unlikely that the end will ever be reached, but we'll cross that bridge when we get there.
I've only ever used the default _id for indexing, and can't figure out how to make this pattern.
Thanks for any insight!
Edit #1
The best solution I've come up with so far is to have a separate .txt file with all of the IDs listed in order. As each new object is created, pop (... shift) the next ID off the top of the file. This might also have the added benefit of easily adding additional IDs at a later date. This will probably be the approach I take, but I'm still interested in the mongoose solution requested above.
Edit #2
So I think the solution I'm going to use is a little different. Basically, findOne sorted by bookID descending. Then use the value returned to set the next.
Material.findOne()
.sort({bookID : -1})
.exec((err, mat) => {
if(err) {
// Send error
}else if(!mat) {
// First bookID
}else {
// Indexes exist...
let nextId = getNextID(mat.bookID);
// ...
}
});
Still easy to modify getNextID() to add new/different IDs in the future (if/when "Z100" is reached)
Thanks again!

Answer 1

Ok, so to expand a little bit on Edit #2, I've come up with the following solution.
Within the model (schema) file, we add a schema pre() middleware, that executes when .save() is called, before the save occurs:
// An arrow function will not work on this guy, if you want to use the "this" keyword
materialSchema.pre('save', function(next) {
this.model('material').findOne() // Don't forget the .model(...) bit!
.sort({bookID : -1}) // All I need is the highest (i.e. most recent) bookID
.select('bookID') // Ditto above (not really necessary)
.exec((err, result) => {
if(err) {
return next(err); // Oopsies, an error!
}else if(!result) {
this.bookID = 'A-001'; // The case when collection is empty
}else {
this.bookID = getNextID(result.bookID); // Otherwise, increment ID
}
next(); // Don't forget this sucker! This is how you save
});
});
And that's about it! It isn't an in-built solution direct from Mongoose, but it works a treat.
Just for completeness, the getNextID function looks like:
function getNextID(curID) {
let letter = curID.split('-')[0];
let number = parseInt(curID.split('-')[1]);
if(number >= 100) { // Increase the letter and reset the number
letter = String.fromCharCode(letter.charCodeAt(0) + 1)
number = '001';
}else { // Only increase the number
number = ('' + (number + 1)).padStart(3, '0'); // Makes sure the numbers are always 3 digits long
}
return `${letter}-${number}`;
}
This'll do just dandy for now. Until we get to Z100. But I'll cross that bridge if/when it comes. No big deal at all.
And you don't need to do anything special to use it. Just save a new doc as normal, and it automatically fires:
new Material({
// New material properties
}).save((err, mat) => {
// Handle errors and returns ...
});