MongoDB query to exclude if id is equal to a document field array value

For this, use $not along with $in. Let us create a collection with documents −

[
   {
      id: "101",
      subjectid: [
         "102"
      ]
   },
   {
      id: "102",
      subjectid: [
         "102"
      ]
   }
]

Here is the snapshot.

Display all documents from a collection with the help of find() method −

db.collection.find()

This will produce the following output −

[
   {
      "_id": ObjectId("5a934e000102030405000000"),
      "id": "101",
      "subjectid": [
         "102"
      ]
   },
   {
      "_id": ObjectId("5a934e000102030405000001"),
      "id": "102",
      "subjectid": [
         "102"
      ]
   }
]

Following is the query that uses $expr, $not and $in to fetch values excluding matching field array value −

db.collection.find({
   $expr: {
      $not:{
         $in: [
            "$id",
            "$subjectid"
         ]
      }
   }
})

This will produce the following output −

[
   {
      "_id": ObjectId("5a934e000102030405000000"),
      "id": "101",
      "subjectid": [
         "102"
      ]
   }
]