In my setupCreateOperation I am successfully using select_from_array to show a multi-select list

         //Get a list of Roles as IDs
         $roles = $this->getRoles();

        CRUD::field([   // select_from_array
            'name'        => 'roles',
            'label'       => 'Roles',
            'type'        => 'select_from_array',
            'options' => $roles->toArray(),
            'allows_null' => false,
            'allows_multiple' => true,
        ]);

But in the setupUpdateOperation I want to show the current choices as already selected, but I can’t see how to do that from the docs. I was expecting something like

        //Get a list of Roles as IDs
        $roles = $this->getRoles();

        //Add an array of roles
        CRUD::field([   // select_from_array
            'name'        => 'roles',
            'label'       => 'Roles',
            'type'        => 'select_from_array',
            'options' => $roles->toArray(),
            'allows_null' => false,
            'selected' => $this->crud->getCurrentEntry()->roles
            'allows_multiple' => true,
        ]);

*I am only trying backpack in my project before I buy to I don’t have Pro and therefore don’t have relationship fields yet