Return List from a web API in C#

Question

tl;dr: I have an API that works in the browser, but I can't figure out how to return a list of items so I can traverse them in a List.

Long version: I'm still struggling with API's and now I've hit another snag. I have the following code in my API:

[Route("api/[controller]")]
    [ApiController]
    public class ScheduleController : Controller
    {
        [HttpGet]
        public IEnumerable<Schedule> GetAllSchedules()
        {
            using (ScheduleDataEntities entities = new ScheduleDataEntities())
            {
                return entities.Schedule.ToList();
            }
        }
        [HttpGet("{id}")]
        public Schedule GetIndividualSchedule(int id)
        {
            using (ScheduleDataEntities entities = new ScheduleDataEntities())
                return entities.Schedule.FirstOrDefault(e => e.ScheduleID == id);
        }
    }

When I navigate to my localhost (https://localhost:7017/api/schedule) it returns the data just fine:

[{"userID":121,"weekDay":"Monday","startTime":"07:00:00","endTime":"07:15:00","createdDate":"2022-01-18T22:11:34.8966667","modifiedDate":"2022-01-18T22:11:34.8966667","active":false,"scheduleID":14414,"dayOfWeek":1,"tsType":"Normal"},
{"userID":94,"weekDay":"Wednesday","startTime":"08:45:00","endTime":"09:00:00","createdDate":"2021-11-03T13:50:50.26","modifiedDate":"2021-11-03T13:50:50.26","active":false,"scheduleID":13160,"dayOfWeek":3,"tsType":"Normal"}
...]

So far, so good. Now, I want to return the list to the client calling the API. I've made a simple test client that should get the list when I press a button:

client.Dispose();
client = new HttpClient();
client.BaseAddress = new Uri("https://localhost:7017/api/schedule/");
client.DefaultRequestHeaders.Accept.Clear();
client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));

List<Schedule> list = GetScheduleList("https://localhost:7017/api/schedule");
//Do something with the list...

However, I can't figure out how this method should work:

static List<Schedule> GetScheduleList(string path)
{
    List<Schedule> schedules = null;
    HttpResponseMessage response = client.GetAsync(path);
    return schedules;
}

Every tutorial I can find online, says to use GetAsync. However, that only works with the await keyword. Adding the await keyword means I have to add the async keyword to my method, which means I must return a Task<List> or a task-like type, which can't be converted to a List. If I return it as a Task, how can I then break it back down into my list of schedules?

I really feel like I've tried anything I've come across, so any help you can give is much appreciated.

your GetScheduleList needs to be async, since you need await in client.GetAsync. Also you need to call your service to get schedules, currently it returns null — Nonik, Feb 22 '22 at 21:07
If you're using .NET Core, please use `IHttpClientFactory`. See [Use IHttpClientFactory to implement resilient HTTP requests](https://learn.microsoft.com/en-us/dotnet/architecture/microservices/implement-resilient-applications/use-httpclientfactory-to-implement-resilient-http-requests) — Heretic Monkey, Feb 22 '22 at 21:08

Serge · Accepted Answer · 2022-02-22T21:12:15.240

0

try this

static async Task<List<Schedule>> GetScheduleList(string path)
{
     var response = await client.GetAsync(path);
    if (response.IsSuccessStatusCode)
    {
        var stringData = await response.Content.ReadAsStringAsync();
        return JsonConvert.DeserializeObject<List<Schedule>>(stringData);
    }
    return null;

and fix the method call

List<Schedule> list =  await GetScheduleList("https://localhost:7017/api/schedule");

or you can try, if you don't use async

List<Schedule> list =  GetScheduleList("https://localhost:7017/api/schedule").Result;

edited Feb 22 '22 at 21:12

answered Feb 22 '22 at 21:07

Serge

40,935
4
18
45

@Serge, I don't think I'll get the chance to try the fix tonight, but I might get a chance tomorrow. I'll let you know if it helps. – starspejd Feb 23 '22 at 17:04

score 0 · Answer 2 · answered Feb 22 '22 at 21:08

did you try to start the web app in debug mode and find the return of the API ? You can even use console.log to give more details;

Otherwise, I was there one day. it's CORS problem. you should add the header : Access-Control-Allow-Origin should have wildcard "*" as a value in order to be able to call https APIs on http servers.

Return List from a web API in C#

2 Answers2