Delete a specific field meeting specific conditions from an object in a collection

Question

I have searched the web for possible solutions. Basically a field needs to be deleted where the id of an object in an array of objects meets a specific condition.

As a newbie to Mongodb I am not sure where exactly to look for relevant examples.

I want to delete the object where id = 0. The language used will be Javascript.

Not quite sure how to go about it though.

Look at the picture below . In red is an id, each registered user will have their own id. Each user will have a cart associated with their id. In the cart is productsInCart-->products which has fields like id, price etc.

So what happens is the users id is selected then the product(object) deleted where the specific product id = 0. The product id is shown with an arrow in the picture and I guess the Object to be deleted would the one at index = 0 also shown by a red arrow. The same could be done with any other Object at index 1 or 2 or anywhere.

I tried using $pull,$unset and the basics found online but the thing is that accessing the product id field requires a very specific command which I am not sure how to write it in Javscript . In sql it would be something Delete Object Where user id = new ObjectId("66a35c99784aa722b15c9801") and product id = 0

Answer 1

Avoid creating nested array fields. This is considered an anti-pattern and introduces unnecessary complexity to the query. Consider keeping just the cart level.

[
  {
    ...,
    "cart": [
      {
        "product": {
          "id": 0,
          "name": "iPad 11inch",
          "imageUrl": "./images/ipad.jpg",
          "title": "Apples",
          "description": "Apples are <span class=\"label label-info\">25 CHF each</span>",
          "price": 25
        },
        "quantity": 2
      },
      ...
    ]
  }
]

You can simplify the query to be like this:

db.collection.update({
  "cart.product.id": 0
},
{
  "$pull": {
    "cart": {
      "product.id": 0
    }
  }
})

Mongo Playground

---

If you need to stick with your current schema, you will need a sophisticated aggregation pipeline. You need to iterate the cart array with $map, then use $filter to iterate through the productsInCart array to perform the filter. Finally, use $mergeObjects to update the result back to cart level.

db.collection.update({
  "cart.productsInCart.product.id": 0
},
[
  {
    "$set": {
      "cart": {
        "$map": {
          "input": "$cart",
          "as": "c",
          "in": {
            "$mergeObjects": [
              "$$c",
              {
                "productsInCart": {
                  "$filter": {
                    "input": "$$c.productsInCart",
                    "as": "p",
                    "cond": {
                      "$ne": [
                        "$$p.product.id",
                        0
                      ]
                    }
                  }
                }
              }
            ]
          }
        }
      }
    }
  }
])

Mongo Playground