mongoose how to count the number of item in array embedded model

Question

Working on Mongoose schema want to count the number of item in cart array how can write the function? Where I want to find particular customer & count the length of the Cart Array

async function countcartproduct(Customer_id){
    console.log(Customer_id);
    const total = await CustomerCart.aggregate([{$match:{Customer_id:Customer_id}},{$project:{Cart:{$size:'$Cart'}}}]);
    console.log(total);
}

var CustomerCart = mongoose.Schema({
    Customer_id:{
       type:mongoose.Schema.Types.ObjectId,
       ref:'Customers'
    },
    Cart:[{
        Product_id:{
             type:String,
             require:true
        },
        Product_Name:{
            type:String,
            require:true,
        },
        Product_Price:{
            type:Number,
            require:true,
        },
        Product_Quantity:{
            type:Number,
            require:true,
            default:1,
        }
    }]
})

Answer 1

the customer id that you are passing is going as a string but it is object id in your schema, so no documents were matching

async function countcartproduct(Customer_id) {
    console.log(Customer_id);
    const total = await CustomerCart.aggregate(
        [{
            $match: {
                Customer_id: mongoose.Types.ObjectId(Customer_id)
            }
        },
        {
            $project: {
                Cart: {
                    $size: '$Cart'
                }
            }
        }]);
    console.log(total);
}

converting it to object id should work