Set selected item via ngModel

a2-forms-select-custom-selection

You don't need to use [attr.selected]. 
[(ngModel)]="user.role" is two-way data-binding, 
it will select the matched option from your list if value is equal to user.role. And you can also use basic [value]

<select name="role" [(ngModel)]="user.role">
    <option *ngFor="let role of roles" [value]="role">{{role.name}}</option>
</select>