C#•5mo ago

✅ How To Use C# To Access FastAPI Server?

I'm not sure if it's possible, maybe it is and I've just not learned it yet, but I use FastAPI for my application backends in languages other than C# as I've been learning the Avalonia Framework more. In that time, I've just been using Microsoft.Data.Sqlite relative databases to storage and access information. I want to switch to using my FastAPI backends instead, I just can't find a tutorial on how to do it. Any suggestions for a good tutorial or youtube videos? Thanks.

33 Replies

Jimmacle•5mo ago

so it's a web api? yes, you can make web requests with C# with httpclient

Angius•5mo ago

You would access that API like you would any other API, in other words

Mekasu0124OP•5mo ago

oh ok. thanks! it would be like the github version service I wrote that makes an http client call to the repo's latest releases. Just different in it's responses

Angius•5mo ago

I'd imagine so, yeah

Mekasu0124OP•5mo ago

awesome. tyvm sorry to bother. Quick question. Again, I'm normally used to using JS and ReactJS and Electron stuff to access FastAPI backends, so this is new to me. So when I run my ReactJS frontend website, or ReactJS+Electron frontend web-app, it gets "hosted" on my local host which gives me an ip address to put in my FastAPI cors middleware allow_origins array. How would I "host" my avalonia application on the local host like that so that it can query the backend? Or do I just run it like normal and I'm overthinking it?

Angius•5mo ago

You... would not The API needs to be hosted and available over the network

Mekasu0124OP•5mo ago

the server is

Angius•5mo ago

Yeah

Mekasu0124OP•5mo ago

it's on my desktop running

Angius•5mo ago

That's enough

Mekasu0124OP•5mo ago

oh ok. I thought I was overthinking it lol

Angius•5mo ago

CORS is a browser thing

Mekasu0124OP•5mo ago

so then I don't need cors_middleware for fastapi then for the application to query it?

Angius•5mo ago

Nope

Jimmacle•5mo ago

cors is a browser-side security feature to prevent malicious scripts from accessing other sites on your behalf as in, if you load a script on sketchywebsite.com that tries to make requests to google's apis your browser won't let it

Mekasu0124OP•5mo ago

got you got you one moment because I think I'm doing something wrong

// MainWindowViewModel.cs
using MathGame.Services;

namespace MathGame.ViewModels;

public partial class MainWindowViewModel : ViewModelBase
{
    private AppServer _server = new();

    public string Greeting => _server.GetRootAsync().Result;
}

// MainWindowViewModel.cs
using MathGame.Services;

namespace MathGame.ViewModels;

public partial class MainWindowViewModel : ViewModelBase
{
    private AppServer _server = new();

    public string Greeting => _server.GetRootAsync().Result;
}

// ./Services/AppServer.cs
using System;
using System.Net.Http;
using System.Threading.Tasks;

namespace MathGame.Services;
public class AppServer
{
    private const string _apiUrl = "http://10.0.0.246:8000/";
    private static HttpClient _client = new();

    public async Task<string> GetRootAsync()
    {
        _client.DefaultRequestHeaders.UserAgent.TryParseAdd("request");

        try
        {
            var response = await _client.GetStringAsync(_apiUrl);
            return response;
        }
        catch (Exception)
        {
            throw;
        }
    }
}

// ./Services/AppServer.cs
using System;
using System.Net.Http;
using System.Threading.Tasks;

namespace MathGame.Services;
public class AppServer
{
    private const string _apiUrl = "http://10.0.0.246:8000/";
    private static HttpClient _client = new();

    public async Task<string> GetRootAsync()
    {
        _client.DefaultRequestHeaders.UserAgent.TryParseAdd("request");

        try
        {
            var response = await _client.GetStringAsync(_apiUrl);
            return response;
        }
        catch (Exception)
        {
            throw;
        }
    }
}

I'm created a default avalonia application using CommunityToolkit.MVVM. I'm just trying to change the greeting to the "Hello, World!" message that the frontend calls to get from the backend

@get_routes.get("/")
async def read_root():
  return { "message": "Hello, World!" }

@get_routes.get("/")
async def read_root():
  return { "message": "Hello, World!" }

Jimmacle•5mo ago

.Result

yes that's wrong

Mekasu0124OP•5mo ago

I thought it was. I wasn't entirely sure what to put there to get the value back

Jimmacle•5mo ago

async calls should be awaited you can't do it in a property getter though, so you'll have to restructure your code

Mekasu0124OP•5mo ago

I do await the call inside of the try/catch oh wait I'm dumb

public partial class MainWindowViewModel : ViewModelBase
{
    private AppServer _server = new();

    public string Greeting = "";

    public MainWindowViewModel()
    {
        
    }

    public async Task<string> MainWindowViewModel()
    {
        Greeting = await _server.GetRootAsync();
    }
}

public partial class MainWindowViewModel : ViewModelBase
{
    private AppServer _server = new();

    public string Greeting = "";

    public MainWindowViewModel()
    {
        
    }

    public async Task<string> MainWindowViewModel()
    {
        Greeting = await _server.GetRootAsync();
    }
}

something like this

Jimmacle•5mo ago

yes and no constructors can't be async

Mekasu0124OP•5mo ago

right. let me look back at my todo app

Jimmacle•5mo ago

if you need to get data asynchronously in order to construct a class, a good pattern is to make the constructor private and add an async factory method

Angius•5mo ago

Can't really have an async factor of an Avalonia window tho

Mekasu0124OP•5mo ago

I'm honestly not too sure. I don't normally practice my avalonia with asynch writing. and this is my first time not only doign that but using fastapi as a backend instead of a relative database that the application uses right there in the client folder inside of a root/Services folder

Angius•5mo ago

Are you using ReactiveUI or Community Toolkit?

Mekasu0124OP•5mo ago

CommunityToolkit

public partial class MainWindowViewModel : ViewModelBase
{
    private AppServer _server = new();

    [ObservableProperty]
    private string _greeting = "";

    public MainWindowViewModel()
    {
        Greeting = GetRoot().Result;
    }

    public async Task<string> GetRoot()
    {
        var result = await _server.GetRootAsync();
        return result;
    }
}

public partial class MainWindowViewModel : ViewModelBase
{
    private AppServer _server = new();

    [ObservableProperty]
    private string _greeting = "";

    public MainWindowViewModel()
    {
        Greeting = GetRoot().Result;
    }

    public async Task<string> GetRoot()
    {
        var result = await _server.GetRootAsync();
        return result;
    }
}

so I had an idea, but it failed. I changed my code to this, however, when I run the application, it doesn't launch the app. It just sits there

Jimmacle•5mo ago

that didn't solve the problem anyway any use of Result is a big code smell unless you have already awaited the task

Mekasu0124OP•5mo ago

it's making the query. The console on the fastapi server shows that root is being accessed with code 200. It' just getting the frontend to do right lol yea I'm trying to figure that part out with you guys. I'm just not that good at it

Angius•5mo ago

There's AsyncRelayCommand https://learn.microsoft.com/en-us/dotnet/communitytoolkit/mvvm/asyncrelaycommand#working-with-asynchronous-commands

Mekasu0124OP•5mo ago

I don't have a command written in though? Unless I should make the greeting change on a button click?

public partial class MainWindowViewModel : ViewModelBase
{
    private readonly AppServer _appServer;

    [ObservableProperty]
    private string _greeting = "Hello, Avalonia!";

    public IRelayCommand FetchGreetingCommand { get; }

    public MainWindowViewModel()
    {
        _appServer = new AppServer();
        FetchGreetingCommand = new AsyncRelayCommand(FetchGreetingAsync);
    }

    private async Task FetchGreetingAsync()
    {
        Greeting = await _appServer.ReadRootAsync();
    }
}

public partial class MainWindowViewModel : ViewModelBase
{
    private readonly AppServer _appServer;

    [ObservableProperty]
    private string _greeting = "Hello, Avalonia!";

    public IRelayCommand FetchGreetingCommand { get; }

    public MainWindowViewModel()
    {
        _appServer = new AppServer();
        FetchGreetingCommand = new AsyncRelayCommand(FetchGreetingAsync);
    }

    private async Task FetchGreetingAsync()
    {
        Greeting = await _appServer.ReadRootAsync();
    }
}

this doesn't work either. "Hello, Avalonia!" displays on the screen instead of "Hello, World!" from the server

public class AppServer
{
    private readonly HttpClient _httpClient;

    public AppServer()
    {
        _httpClient = new HttpClient
        {
            BaseAddress = new Uri("http://10.0.0.246:8000/")
        };
    }

    public async Task<string> ReadRootAsync()
    {
        try
        {
            HttpResponseMessage response = await _httpClient.GetAsync("/");
            response.EnsureSuccessStatusCode();

            string content = await response.Content.ReadAsStringAsync();
            return content;
        }
        catch (Exception ex)
        {
            return $"Error: {ex.Message}";
        }
    }
}

public class AppServer
{
    private readonly HttpClient _httpClient;

    public AppServer()
    {
        _httpClient = new HttpClient
        {
            BaseAddress = new Uri("http://10.0.0.246:8000/")
        };
    }

    public async Task<string> ReadRootAsync()
    {
        try
        {
            HttpResponseMessage response = await _httpClient.GetAsync("/");
            response.EnsureSuccessStatusCode();

            string content = await response.Content.ReadAsStringAsync();
            return content;
        }
        catch (Exception ex)
        {
            return $"Error: {ex.Message}";
        }
    }
}

that's my AppServer that I'm using to connect tot he fast api

Angius•5mo ago

I'll take a look tomorrow. Haven't used Avalonia much myself, let alone in an async context

Mekasu0124OP•5mo ago

ok I appreciate iti ❤️

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✅ How To Use C# To Access FastAPI Server?