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Update dependency-injection.md (#8611) 

Elaborated on the recommendation to avoid Service Locator pattern
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Kyle Burns 2018-10-09 15:18:08 -04:00 committed by Rick Anderson
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aspnetcore/fundamentals/dependency-injection.md
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@ -534,17 +534,17 @@ The factory method of single service, such as the second argument to [AddSinglet
When working with dependency injection, keep the following recommendations in mind:
* Avoid storing data and configuration directly in the service container. For example, a user's shopping cart shouldn't typically be added to the service container. Configuration should use the [options pattern](xref:fundamentals/configuration/options). Similarly, avoid "data holder" objects that only exist to allow access to some other object. It's better to request the actual item via dependency injection, if possible.
* Avoid storing data and configuration directly in the service container. For example, a user's shopping cart shouldn't typically be added to the service container. Configuration should use the [options pattern](xref:fundamentals/configuration/options). Similarly, avoid "data holder" objects that only exist to allow access to some other object. It's better to request the actual item via DI.
* Avoid static access to services (for example, statically-typing [IApplicationBuilder.ApplicationServices](/dotnet/api/microsoft.aspnetcore.builder.iapplicationbuilder.applicationservices) for use elsewhere).
* Avoid using the service locator pattern (for example, [IServiceProvider.GetService](/dotnet/api/system.iserviceprovider.getservice)).
* Avoid using the *service locator pattern*. For example, don't invoke <xref:System.IServiceProvider.GetService*> to obtain a service instance when you can use DI instead. Another service locator variation to avoid is injecting a factory that resolves dependencies at runtime. Both of these practices mix [Inversion of Control](/dotnet/standard/modern-web-apps-azure-architecture/architectural-principles#dependency-inversion) strategies.
* Avoid static access to `HttpContext` (for example, [IHttpContextAccessor.HttpContext](/dotnet/api/microsoft.aspnetcore.http.ihttpcontextaccessor.httpcontext)).
Like all sets of recommendations, you may encounter situations where ignoring a recommendation is required. Exceptions are rare&mdash;mostly special cases within the framework itself.
Dependency injection is an *alternative* to static/global object access patterns. You may not be able to realize the benefits of dependency injection if you mix it with static object access.
DI is an *alternative* to static/global object access patterns. You may not be able to realize the benefits of DI if you mix it with static object access.
## Additional resources