how to delete sub doc only on expire using mongoose? - node.js

Question

I have problem deleting subdocument from collection 1, when document in collection 2 is expire.
I have cart schema like below.
var cartSchema = new schema({
userName : {type: String, default: null},
total : {type: Number, default: 0},
qty : {type: Number, default: 0},
productId : {type: String, default: null},
createdAt : {type: Date, default: Date.now, expires: 7200} // expired in 2 hours
});
and here I have schema which save object carted related to cartSchema
var merchantSchema = new schema({
seller : String,
address : String,
email : String,
products : [
{
title : String,
ingredients : String,
qty : Number,
carted : [
{
qty : Number,
cartId : String,
createdAt : {type: Date, default: Date.now}
}
}
],
});
since expireAt query runs automatically, I don't know how to delete automatically carted object when cart expired and deleted.
when cart in cartSchema with id 123 expired and deleted, so cart in carted object with id 123 will also be deleted.
if I add expires property in merchantSchema createdAt : {type: Date, default: Date.now, expires: 7200}, it will delete whole document.

Answer 1

You can't use a TTL index to delete sub-document.
One workaround could be done through change your data schema through population as below
var merchantSchema = new schema({
seller : String,
address : String,
email : String,
products : [productSchema],
});
var Merchant = mongoose.model('Merchant', merchantSchema);
var productSchema = new Schema({
title : String,
ingredients : String,
qty : Number
});
var Product = mongoose.model('Product', productSchema);
var cartSchema = new schema({
userName : {type: String, default: null},
total : {type: Number, default: 0},
qty : {type: Number, default: 0},
productId : {type: Schema.Types.ObjectId, ref: 'Product'},
createdAt : {type: Date, default: Date.now, expires: 7200} // expired in 2 hours
});
Then the createdAt expires, then the cart document will be deleted, and there is no cart information related to product document.