Could I get "currentDoc" and "_id" on custom validate of "updateForm" for SimpleSchema?

I create custom validation with difference operation

...............
custom: function () {
            if (Meteor.isServer && this.isSet) {
                // Insert
                if (!this.operator) {
                    console.log('insert:');
                    return locationIsExists(Collection, selector);
                } else {// Update
                    console.log('update: ');
                    // would like to get _id and currentDoc
                    return locationIsExists(Collection, selector);
                }
            }
        }

In the update operation, I would like to get the _id and currentDoc.
Please help me.

Now I can with this.docId for update form.