Mongodb- Query to check if a field in the json array exists or not

Question

I have a JSON in MongoDB and I am trying to check if at least one of the items in the JSON doesn't contain a specific field.

{
    "_id" : 12345,
     "orderItems" : [ 
        { 
            "itemId" : 45678,
            "isAvailable" : true,
            "isEligible" " false
        },
        {
             "itemId" : 87653,
             "isAvailable" : true
         }
   ]
}

So in the above JSON, since the 2nd one under order items doesn't contain iseligible field, I need to get this _id.

I tried the below query so far, which didnt work:

db.getCollection('orders').find({"orderItems.iseligible":{$exists:false})

If iseligible doesnt exist for any of the items, I need that complete document to be displayed. For eg., have 2 documents: { "_id" : 12345, "orderItems" : [ { "itemId" : 45678, "isAvailable" : true, "isEligible" " false }, { "itemId" : 87653, "isAvailable" : true } ] } { "_id" : 12346, "orderItems" : [ { "itemId" : 45678, "isAvailable" : true, "isEligible" " false }, { "itemId" : 87653, "isEligibe": false, "isAvailable" : true } ] } In the above example, the output should return first document since it doesnt contain isEligible for one of the item — Ajay
– Ajay, Commented Nov 11, 2021 at 20:32

It'sNotMe · Accepted Answer · 2021-11-11 20:36:12Z

1

You can use $elemMatch to evaluate the presence of the nested key. Once that's accomplished, project out the _id value.

db.orders.find({
  orderItems: {
    $elemMatch: {
      "isEligible": {
        $exists: false
      }
    }
  }
},
{
  _id: 1
})

Here is a Mongo playground with the finished code, and a similar SO answer.

answered Nov 11, 2021 at 20:36

It'sNotMe

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