ASP.NET Core initialize singleton after configuring DI

c# asp.net-core dependency-injection singleton
pbz picture pbz · Aug 17, 2016 · Viewed 34.3k times · Source

So let's say I have a singleton class instance that I register in the DI like this:

services.AddSingleton<IFoo, Foo>();

And let's say the Foo class has a number of other dependencies (mostly repository classes that allow it to load data).

With my current understanding, the Foo instance is not created until it's first used (asked). Is there a way to initialize this class other than the constructor? Like right after ConfigureServices() completes? Or should the initialization code (loading data from db) be done in Foo's constructor?

(It would be nice if this class could load its data before the first use to speed up first time access)

Answer

Tseng picture Tseng · Aug 17, 2016

Do it yourself during startup. 

var foo = new Foo();
services.AddSingleton<IFoo>(foo);

Or "warm it up"

public void Configure(IApplicationBuilder app) 
{
    app.ApplicationServices.GetService<IFoo>();
}

or alternatively 

public void Configure(IApplicationBuilder app, IFoo foo) 
{
    ...
}

But this feels just dirty and is more a problem with your design, if you do something that you shouldn't in the constructor. Class instantiation has to be fast and if you do long-running operations within it, you break against a bunch of best practices and need to refactor your code base rather than looking for ways to hack around it

Related questions

ASP.NET Core Dependency Injection error: Unable to resolve service for type while attempting to activate

I created an .NET Core MVC application and use Dependency Injection and Repository Pattern to inject a repository to my controller. However, I am getting an error: InvalidOperationException: Unable to resolve service for type 'WebApplication1.Data.BloggerRepository' while attempting to …

Read More
Resolving instances with ASP.NET Core DI from within ConfigureServices

How do I manually resolve a type using the ASP.NET Core MVC built-in dependency injection framework? Setting up the container is easy enough: public void ConfigureServices(IServiceCollection services) { // ... services.AddTransient<ISomeService, SomeConcreteService>(); } But how can I resolve …

Read More
.NET Core DI, ways of passing parameters to constructor

Having the following service constructor public class Service : IService { public Service(IOtherService service1, IAnotherOne service2, string arg) { } } What are the choices of passing the parameters using .NET Core IOC mechanism _serviceCollection.AddSingleton<IOtherService , OtherService>(); _serviceCollection.AddSingleton<IAnotherOne , …

Read More