如何正确使用“async”和“await”使应用程序异步？

Question

class Website
{
    public Website(string link)
    {
        _linkToWeb = new RestClient(link);
    }
    public async Task<string> DownloadAsync(string path)
    {
        var request = new RestRequest(path, Method.GET);
        var response = _linkToWeb.ExecuteAsync(request);
        return response.Result.Content;
    }
    public RestClient _linkToWeb { get; set; }
}

class Program
{
    public static Website API = new Website("https://api.collegefootballdata.com");
    public static async Task<string> _downloadTeamsFromAPI()
    {
        return API.Download("/teams/fbs");
    }
    public static async Task<string> _downloadAdvancedInfoFromAPI()
    {
        return API.Download("/stats/season/advanced?year=2010");
    }
    public static async Task<Teams> _addTeamToDB(Teams item)
    {
        var tmp = new Teams
        {
            School = item.School,
            Abbreviation = item.Abbreviation,
            Conference = item.Conference,
            Divison = item.Divison,
            Color = item.Color,
            Alt_Color = item.Alt_Color,
            Team = await _getAdvancedInfoFromAPI(item.Conference)
        };
        return tmp;
    }
    public static async Task<string> _getAdvancedInfoFromAPI(string _conferenceName)
    {
        List<Advanced> advancedDataList = new List<Advanced>();
        var advancedData = await _downloadAdvancedInfoFromAPI();
        var advancedDataDeserialized = JsonSerializer.Deserialize<Advanced[]>(advancedData, new JsonSerializerOptions()
        {
            PropertyNameCaseInsensitive = true
        });

        foreach (var item in advancedDataDeserialized)
        {
            advancedDataList.Add(new Advanced
            {
                Team =                  item.Team,
                //Conference =            item.Conference,
                Year =                  item.Year,
                excludeGarbageTime =    item.excludeGarbageTime,
                startWeek =             item.startWeek,
                endWeek =               item.endWeek
            });
        }
        return await _lookForMatch(_conferenceName, advancedDataList);
    }
    public static async Task<string> _lookForMatch(string _Confa, List<Advanced> lista)
    {
        return lista
                        .Where(x => x.Conference == _Confa)
                        .Select(x => x.Team)
                        .FirstOrDefault();
    }
    public static async Task Main()
    {
        Console.WriteLine("Odpaliłem program!\n");
        using var db = new Context();
        db.Database.EnsureCreated();
        Console.WriteLine("Stworzylem baze!\n");
        var teams = await _downloadTeamsFromAPI();

        var deserializer = JsonSerializer.Deserialize<Teams[]>(teams, new JsonSerializerOptions()
        {
            PropertyNameCaseInsensitive = true
        });
        Console.WriteLine("Zdeserializowalem dane!\n");
        foreach (var item in deserializer)
        {
            db.Teams.Add(await _addTeamToDB(item));
            Console.WriteLine(DateTime.Now.ToString("HH:mm:ss"));
            Console.WriteLine("Dodalem element do bazy...\n");
        };
        db.SaveChanges();
        Console.WriteLine("Zapisalem dane do bazy!");
    }
} 

I know it's a noob question but I don't know how to make it work :/

I want to make it a bit asynchronous, because the words async and await doesn't exactly make it more asynchronous, but I don't know how to make it work anyhow asynchronous.

The app first downloads the information from API, deserializes it and stores it into var type variable. Then it downloads the advanced info from API and joins it by "Conference" item. (that is on purpose, even though it's not optimal).

There are a lot of async s and await s but I don't think it anyhow runs asynchronously. What should I change to make this app actually async?

Answer 1

I appreciate your motive to write asynchronous code to make your application more scalable. However after going through the sample code posted, I am afraid you need to do more learning on the concepts of asynchronous programming rather than just jumping into the console and trying to write some code which looks like asynchronous code.

Start slowly and try to understand the purpose of Task library, when to use it. What await does behind the scenes. When to wrap a return type with Task and when to mark a method as async . These are some of the main keywords which you come across in asynchronous code and a good understanding of these is a must to write/understand asynchronous code.

There are plenty of resources available online to get a hang of these concepts. For starters, you can begin looking into Microsoft Documentation

Having said that, inline is a rewrite of the sample code with proper use of async/await . Please use this for references purpose only. Do not try to put into some production code until unless you have a good understanding of the concept.

Necessary comments are provided to explain some critical changes made.

class Website
{
    public Website(string link)
    {
        _linkToWeb = new RestClient(link);
    }

    public async Task<string> DownloadAsync(string path)
    {
        var request = new RestRequest(path, Method.GET);
        var response = await _linkToWeb.ExecuteAsync(request); //await an asynchronous call.
        return response.Content; //No need to call response.Result. response content can be fetched after successful completion of asynchronous call.
    }
    public RestClient _linkToWeb { get; set; }
}

class Program
{
    public static Website API = new Website("https://api.collegefootballdata.com");

    public static async Task<string> _downloadTeamsFromAPI()
    {
        return await API.DownloadAsync("/teams/fbs");
    }

    public static async Task<string> _downloadAdvancedInfoFromAPI()
    {
        return await API.DownloadAsync("/stats/season/advanced?year=2010");
    }

    public static async Task<Teams> _addTeamToDB(Teams item)
    {
        var tmp = new Teams
        {
            School = item.School,
            Abbreviation = item.Abbreviation,
            Conference = item.Conference,
            Divison = item.Divison,
            Color = item.Color,
            Alt_Color = item.Alt_Color,
            Team = await _getAdvancedInfoFromAPI(item.Conference)
        };
        return tmp;
    }

    //Return type has to be Task<Teams> rather than Task<string> because the return object is Teams.
    public static async Task<Teams> _getAdvancedInfoFromAPI(string _conferenceName)
    {
        List<Advanced> advancedDataList = new List<Advanced>();
        var advancedData = await _downloadAdvancedInfoFromAPI();
        var advancedDataDeserialized = JsonSerializer.Deserialize<Advanced[]>(advancedData, new JsonSerializerOptions()
        {
            PropertyNameCaseInsensitive = true
        });

        foreach (var item in advancedDataDeserialized)
        {
            advancedDataList.Add(new Advanced
            {
                Team = item.Team,
                //Conference =            item.Conference,
                Year = item.Year,
                excludeGarbageTime = item.excludeGarbageTime,
                startWeek = item.startWeek,
                endWeek = item.endWeek
            });
        }
        return _lookForMatch(_conferenceName, advancedDataList);
    }

    //Return type is Teams and not string. 
    //Moreover Task<string> not required because we are not awaiting method call in this method.
    public static Teams _lookForMatch(string _Confa, List<Advanced> lista) 
    {
        return lista.Where(x => x.Conference == _Confa)
                        .Select(x => x.Team)
                        .FirstOrDefault();
    }

    public static async Task Main()
    {
        Console.WriteLine("Odpaliłem program!\n");
        using var db = new Context();
        db.Database.EnsureCreated();
        Console.WriteLine("Stworzylem baze!\n");
        var teams = await _downloadTeamsFromAPI();

        var deserializer = JsonSerializer.Deserialize<Teams[]>(teams, new JsonSerializerOptions()
        {
            PropertyNameCaseInsensitive = true
        });
        Console.WriteLine("Zdeserializowalem dane!\n");
        foreach (var item in deserializer)
        {
            db.Teams.Add(await _addTeamToDB(item));
            Console.WriteLine(DateTime.Now.ToString("HH:mm:ss"));
            Console.WriteLine("Dodalem element do bazy...\n");
        };
        db.SaveChanges();
        Console.WriteLine("Zapisalem dane do bazy!");
    }
}