Can I restrict a mutation to update an object based on the object itself?

Question

I have the following objects in my database:

[
    {
        "id": 1,
        "name": "foo",
        "objType": "A"
    },
    {
        "id": 2,
        "name": "bar",
        "objType": "B"
    }
]

And the following users:

[
    {
        "id": 3,
        "name": "User A",
        "role": "admin"
    },
    {
        "id": 4,
        "name": "User B",
        "role": "client"
    }
]

And I have a schema like:

enum ObjTypeEnum {
    A
    B
}

type MyObj {
    id: Int
    name: String
    objType: ObjTypeEnum
}

type Mutation {
    updateObj(id: Int!, name: String): MyObj
}

The user A can update any obj that he wants because he is an admin. However, the user B can only update an object only if this object is of type B.

That means: If the user B tries to update the object 2, using the mutation updateObj(2, "new name"), this should be totally ok. However, if he tries to update the object 1, updateObj(1, "new name"), now this should return an error for this user.

My naïve solution for this is get the object in the resolver, check its type and, if is ok for the current user, then proceed with the update, otherwise throw an error. But I have the feeling I'm in the wrong direction and not using graphql properly...

Is it possible to do it using directives or something more generic, since the key that using to validate the update is an enum?