Why isn't MongoDB update working in a Meteor Method?

Question

I was trying the following Meteor method, but it seems it is not working. Because when I check my DB, I cannot find the updated information.

const Employees = new Mongo.Collection("Employees");
Employees.attachSchema(Schemas.Employee, { selector: { type: "fullTime" } });
Employees.attachSchema(Schemas.EmployeeVariant, { selector: { type: "partTime" } });

Meteor.methods({
  "employees/updateTasks": function (employeeId, taskId) {
    this.unblock();

    //the following is printed.
    console.log("employeeId: "+employeeId+" taskId:"+ taskId);
    return Employees.update({_id: employeeId}, 
        {$push: {tasks: taskId}}, 
        {selector: {type: "fullTime"}});
  }
});

Is there anything obvious wrong here?

Another question is:

Sometimes I see people using it this way:

Employees.update(employeeId,  // not {_id:employeeId}
            {$push: {tasks: taskId}}, 
            {selector: {type: "fullTime"}}); 

It is being used here: "5.3 Add event handlers for Task buttons"

Why is this?

My Mongodb's version is 3.2.6

Answer 1

It turns out that collection hooks (https://github.com/matb33/meteor-collection-hooks) are used here. There is a Employees.before.update method to check what to do before "Employees.update" really happens.