46 lines
1.9 KiB
Markdown
46 lines
1.9 KiB
Markdown
---
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uid: FAQ.Basics.DI
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title: Questions about Dependency Injection
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---
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# Dependency Injection-related Questions
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In the following section, you will find common questions and answers
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to utilizing dependency injection with @Discord.Commands and @Discord.Interactions, as well as
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common troubleshooting steps regarding DI.
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## What is a service? Why does my module not hold any data after execution?
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In Discord.Net, modules are created similarly to ASP.NET, meaning
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that they have a transient nature; modules are spawned whenever a
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request is received, and are killed from memory when the execution
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finishes. In other words, you cannot store persistent
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data inside a module. Consider using a service if you wish to
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workaround this.
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Service is often used to hold data externally so that they persist
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throughout execution. Think of it like a chest that holds
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whatever you throw at it that won't be affected by anything unless
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you want it to. Note that you should also learn Microsoft's
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implementation of [Dependency Injection] \([video]) before proceeding.
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A brief example of service and dependency injection can be seen below.
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[!code-csharp[DI](samples/DI.cs)]
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[Dependency Injection]: https://docs.microsoft.com/en-us/aspnet/core/fundamentals/dependency-injection
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[video]: https://www.youtube.com/watch?v=QtDTfn8YxXg
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## Why is my Command/Interaction Service complaining about a missing dependency?
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If you encounter an error similar to `Failed to create MyModule,
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dependency MyExternalDependency was not found.`, you may have
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forgotten to add the external dependency to the dependency container.
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For example, if your module, `MyModule`, requests a `DatabaseService`
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in its constructor, the `DatabaseService` must be present in the
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[IServiceProvider] when registering `MyModule`.
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[!code-csharp[Missing Dependencies](samples/missing-dep.cs)]
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[IServiceProvider]: xref:System.IServiceProvider
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