public async Task<IdentityResult> AssignRole(int userId, string roleName)
{
    IUser usr = await this.DBContext.Context.IdentityUsers.FirstOrDefaultAsync(r => r.Id.Equals(userId));

    this.DBContext.Context.Detach(usr);

    var result = await _user.AddToRoleAsync((User)usr, roleName);

    return result;
}

public void Detach(ILCAssetsBase entity)
{
    this.Entry(entity).State = EntityState.Detached;
}