MongoDB-mongoose, Array filter

Question

I have an issue with array object.

    "userId": "63317e7f9746ba9719845b6e",
    "items": [
        {
            "productId": "Z357",
            "piece": 1,
            "_id": "63333427d7ea226b2462e734"
        },
        {
            "productId": "A541",
            "piece": 1,
            "_id": "6333342cd7ea226b2462e738"
        },
        {
            "productId": "G31",
            "piece": 1,
            "_id": "633334ea1ca2b582ddd0bc62"
        },
        {
            "productId": "K1123",
            "piece": 1,
            "_id": "6333351028b43b58b8f83ba3"
        }
    ],

I have an array like that. I want to get specific item with productId,

const checker = await Cart.findOne({
      "items.productId": productId,
    });

I'm checking an array like that, but it's giving me all of the items that contain productId, how can I get only what am I filter?

Answer 1

You can try this way with projection to get only the matched element where your productId is equal to the provided productId ,

const checker = await Cart.findOne({items:{ $elemMatch:{ productId: productId}}},
  {userId:1,"items.$": 1});

Answer 2

For get the specific item with a given productId, you need to use the $elemMatch operator in your query:

 const checker = await Cart.findOne({ "items": { "$elemMatch": { "productId": productId } } });

The $elemMatch operator matches documents where the value of the specified field is an array that contains at least one element that matches the specified condition. In this case, it returns the first item in the items array that matches the productId condition.