对web api的2次连续调用不会返回更新的结果集

Question

当我第一次打电话到我的网页api时

GetAssignedRoles/{userID} 

它第一次有效。后续调用返回相同的结果集，直到我再次调用此方法之前调用另一个方法

[HttpGet("GetAssignedRoles/{userID}")]
    public async Task<IActionResult> GetAssignedRoles(string userID)
    {
        ApplicationUser user = await _userManager.FindByIdAsync(userID);
        IList<string> roles = await _userManager.GetRolesAsync(user);
        List<UserRole> userRoles = new List<UserRole>();
        foreach(var item in roles)
        {
            userRoles.Add(await _roleManager.FindByNameAsync(item));
        }
        IEnumerable<UserRoleViewModel> roleViewModel = Mapper.Map<IEnumerable<UserRole>, IEnumerable<UserRoleViewModel>>(userRoles);
        return new OkObjectResult(roleViewModel);
    }