How to setup database connections only once from startup in .NET Core?

Question

I am newbiew in dotnet/c# and trying to learn. I am writing a server app that connects/init to different database. one is MongoDB. then I have a config microservice. how do I save the connection string that I got from my config-server? from these MongoDB example, I need to pass the connection string. but I don't want to get it from the config-server every time.

Read some tutorials from here about dependency injection, not sure if this is really what I need.

Here is my tryout code..

my configservice that I want to setup or act as getter/setter

public class Configctl : IDisposable
{
    public static string env;
    public Configctl()
    {
        env = Environment.GetEnvironmentVariable("ASPNETCORE_ENVIRONMENT");
        Console.WriteLine($"ASPNETCORE_ENVIRONMENT/env={env}");
    }

    public static void ConfigureMongodb()
    {
        Console.WriteLine($"configure mongodb..");
        // var config = await getConfig()
    }
}

MongdbContext that I want to fill the MongoUrl from the Configctl without getting from the Configctl each time.

public class MongdbContext<T> : IDisposable
{
    public IMongoDatabase _database { get; }
    public IMongoClient _client;
    public MongdbContext()
    {
        var settings = MongoClientSettings.FromUrl(GetMongoURL());
        _client = new MongoClient(settings);
        _database = _client.GetDatabase("testdb");
    }

    public void Dispose()
    {
        Console.WriteLine("mongodb disposed");
    }

    public static MongoUrl GetMongoURL()
    {
        return new MongoUrl("mongodb://user:pass@host:27017/admin");
    }
}

and for experiment, I tried calling Configctl from ConfigureServices. I maybe wrong..

    public void ConfigureServices(IServiceCollection services)
    {
        services.AddSingleton(new Configctl());

        services.AddMvc();
    }

Ilya Chumakov · Accepted Answer · 2017-04-26 13:29:05Z

2

If you don't need to read options from external service each time, then just read it on application start, bind to a POCO and register the POCO as singleton. Then pass the POCO as dependency to your MongdbContext.

Options reader example:

class OptionsReader
{
    public MyOptions GetMyOptions()
    {
         //call to external config microservice, db, etc.
    }
}

Services registration in Startup class:

public void ConfigureServices(IServiceCollection services)
{    
    services.AddTransient<OptionsReader>();
    services.AddSingletonFromService<OptionsReader, MyOptions>(x => x.GetMyOptions());
}

Useful extention method:

public static void AddSingletonFromService<TService, TOptions>(
    this IServiceCollection services,
    Func<TService, TOptions> getOptions)
    where TOptions : class
    where TService : class
{
    services.AddSingleton(provider =>
    {
        var service = provider.GetService<TService>();

        TOptions options = getOptions(service);

        return options;
    });
}

Options consumer:

class MongdbContext
{
    public MongdbContext(MyOptions options)
    {
    }
}

answered Apr 26, 2017 at 13:29

Ilya Chumakov

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1 Comment

Hokutosei Over a year ago

this looks fantastic and clean. I'm going to try this one now. thank you

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