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mongoose node.js

How to set ObjectId as a data type in mongoose

Using node.js, mongodb on mongoHQ and mongoose. I’m setting a schema for Categories. I would like to use the document ObjectId as my categoryId.

var mongoose = require('mongoose');
var Schema = mongoose.Schema,
ObjectId = Schema.ObjectId;
var Schema_Category = new Schema({
categoryId : ObjectId,
title : String,
sortIndex : String
});

I then run

var Category = mongoose.model('Schema_Category');
var category = new Category();
category.title = "Bicycles";
category.sortIndex = "3";
category.save(function(err) {
if (err) { throw err; }
console.log('saved');
mongoose.disconnect();
});

Notice that I don’t provide a value for categoryId. I assumed mongoose will use the schema to generate it but the document has the usual “_id” and not “categoryId”. What am I doing wrong?

Unlike traditional RBDMs, mongoDB doesn’t allow you to define any random field as the primary key, the _id field MUST exist for all standard documents.

For this reason, it doesn’t make sense to create a separate uuid field.

In mongoose, the ObjectId type is used not to create a new uuid, rather it is mostly used to reference other documents.

Here is an example:

var mongoose = require('mongoose');
var Schema = mongoose.Schema,
ObjectId = Schema.ObjectId;
var Schema_Product = new Schema({
categoryId : ObjectId, // a product references a category _id with type ObjectId
title : String,
price : Number
});

As you can see, it wouldn’t make much sense to populate categoryId with a ObjectId.

However, if you do want a nicely named uuid field, mongoose provides virtual properties that allow you to proxy (reference) a field.

Check it out:

var mongoose = require('mongoose');
var Schema = mongoose.Schema,
ObjectId = Schema.ObjectId;
var Schema_Category = new Schema({
title : String,
sortIndex : String
});
Schema_Category.virtual('categoryId').get(function() {
return this._id;
});

So now, whenever you call category.categoryId, mongoose just returns the _id instead.

You can also create a “set” method so that you can set virtual properties, check out this link
for more info