Deleting an item with condition in MongoDB? - mongodb

Question

I want to remove a product from the Cart by checking its quantity. Its quantity should be decremented by 1 unless it reaches zero, and after that, it should pull out from the product array of the Cart.
here is my Logic : (I want to perform the pull and decrement operation inside the single query. But I m stuck on how to perform these two operations together by a simple condition in MongoDb)
const cart = await Cart.findOneAndUpdate({"products.productId": req.body.productId}, {$inc: {"products.$.quantity": -1}}, {new: true})
await Cart.update({"products.productId": req.body.productId}, {$pull: {quantity: 0}})
here is the model for clarification:
import mongoose from 'mongoose';
const cartSchema = new mongoose.Schema({
userId: {
type: String,
required: true,
},
products: [
{
productId: {
type: String,
},
quantity: {
type: Number,
default: 1
}
}
]
}, {timestamps: true});
const Cart = new mongoose.model('Cart', cartSchema);
export default Cart;
Thanks :)

Answer 1

There is no straight way to do this in single regular update query.
To improve your approach you can try this,
first query to check productId and quantity should greater than 1
const cart = await Cart.updateOne(
{
products: {
$elemMatch: {
productId: req.body.productId,
quantity: { $gt: 1 }
}
}
},
{ $inc: { "products.$.quantity": -1 } }
);
Playground
second query if the first query's result is nModified is 0 then pull the product, by checking condition productId and quantity equal-to 1
if (cart.nModified === 0) {
await Cart.updateOne(
{
products: {
$elemMatch: {
productId: req.body.productId,
quantity: { $eq: 1 }
}
}
},
{ $pull: { products: { productId: req.body.productId } } }
)
}
Playground
If you really want to do using single query you can try update with aggregation pipeline starting from MongoDB 4.2,
$map to iterate loop of products array and check condition, if the productId matches then increment/decrement quantity by $add operator otherwise return current quantity
$filter to iterate loop of above result and check condition if productId and quantity is not zero
await Cart.updateOne(
{ "products.productId": req.body.productId },
[{
$set: {
products: {
$filter: {
input: {
$map: {
input: "$products",
in: {
productId: "$$this.productId",
quantity: {
$cond: [
{ $eq: ["$$this.productId", req.body.productId] },
{ $add: ["$$this.quantity", -1] },
"$$this.quantity"
]
}
}
}
},
cond: {
$and: [
{ $eq: ["$$this.productId", req.body.productId] },
{ $ne: ["$$this.quantity", 0] }
]
}
}
}
}
}
])
Playground