Does hasMany require an inverse relationship?

Ember Data
1

In my app I have two models task and package. A package can contain multiple tasks and a single task can belongs to multiple packages. I currently have the models defined as:

App.Package = DS.Model.extend({
    id: DS.attr('number'),
    tasks: DS.hasMany('task', { async: true })
    // other package properties
});

App.Task = DS.Model.extend({
    id: DS.attr('number'),
    // other task properties
});

Do I need to has a hasMany('package') relationship to App.Task? In the application the relationship is only defined at the package level - a task can be added to a package but a package cannot be added to a task.