$exclude

In MongoDB, the projection operators help you to specify the fields you want to include or exclude in the query result. The exclude operator, as the name suggests, helps you to exclude certain fields from the result.

To exclude a field from the query result, you need to set its value to 0 in the projection document. Let's understand it better with an example.

Syntax

{
    $project: {
        field1: 0,
        field2: 0
        ...
    }
}

Here, we're specifying that the fields field1 and field2 should be excluded from the result.

Example

Suppose we have a collection called students with the following documents:

{
    "_id": 1,
    "name": "John Doe",
    "age": 20,
    "course": "Software Engineering"
},
{
    "_id": 2,
    "name": "Jane Smith",
    "age": 22,
    "course": "Computer Science"
},
{
    "_id": 3,
    "name": "Richard Roe",
    "age": 21,
    "course": "Information Technology"
}

Now, let's say we want to fetch all the students but exclude the age field from the result. We can achieve this using the following command:

db.students.aggregate([
  {
    $project: {
      age: 0,
    },
  },
]);

This command will return the following result:

{
    "_id": 1,
    "name": "John Doe",
    "course": "Software Engineering"
},
{
    "_id": 2,
    "name": "Jane Smith",
    "course": "Computer Science"
},
{
    "_id": 3,
    "name": "Richard Roe",
    "course": "Information Technology"
}

As you can see, the age field is excluded from the result.

Note: You cannot use the exclude operator (0) for a field that is explicitly included with the include operator (1) in the same document, except for the _id field. The _id field is the only field that can have both exclude (0) and include (1) options in the same document.