Mongoose validation value from another table - node.js

Question

This is my Product table schema
let schema = new mongoose.Schema({
title: {type: String, required: true},
price: {type: Number, required: true},
description: {type: String, required: true},
sizes: {type: Object, required: true},
offer: {type: Number, default: 0},
images: {type: Array, required: true},
deal: {type: Boolean, default: false},
category: {
_id: {type: Schema.Types.ObjectId, required: true},
name: {type: String, required: true}
},
company_name: {type: String, required: true}
});
What I am trying to do
I am trying to validate if category.name value equal exist in my another table called Category.

Answer 1

You could use an async validator and query the categories collection. Something like this (using promise sytax for validator):
let schema = new mongoose.Schema({
title: {type: String, required: true},
price: {type: Number, required: true},
description: {type: String, required: true},
sizes: {type: Object, required: true},
offer: {type: Number, default: 0},
images: {type: Array, required: true},
deal: {type: Boolean, default: false},
category: {
_id: {type: Schema.Types.ObjectId, required: true},
name: {
type: String,
required: true,
validate: function(nameVal) {
return new Promise(function(resolve, reject) {
let Category = mongoose.model('Category'); //you would have to be sure that Category model is loaded before this one. One reason not to do this
Category.findOne({name: nameVal}, (err, cat) => resolve(cat ? true : false)); //any non null value means the category was in the categories collection
});
}
}
},
company_name: {type: String, required: true}
});
Some thoughts about this:
This is documented at http://mongoosejs.com/docs/validation.html#async-custom-validators.
As it states there, the validator is not run by default on updates. There are a lot of caveats to read through there.
In my experience with NoSQL DBs, the code creating a new Product would take care to make sure the category being assigned was valid. The code probably found the category from the DB at some point prior. So having a validator lookup would be redundant. But you may have a situation where you have a lot of code that creates Products and want validation in one place.
When I see that you are storing a document of {_id: ..., name: ...} as the category field in your Product schema, I think you might want this instead:
...
category: {Schema.Types.ObjectId, ref: 'Category'},
This allows you to store a reference to a category you have retrieved from the categories collection. Mongoose will load up the category document inline for you when you retrieve the products, if you use the populate method on your query. See http://mongoosejs.com/docs/populate.html. There are a lot of options with the populate functionality you might find useful. It does not do validation that the category is valid on save, as far as I know. But if you take this approach, you would have already looked up the category previously in the code before your save (see the link to get a better idea what I mean). Essentially this gives you join like behavior with MongoDB, with the storage savings and other benefits one expects from "normalization".