WEBVTT

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Hi everyone.

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In this video let's talk about one important topic.

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I will call it a circular dependency.

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So what exactly is a circular dependency.

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So you can see the documentation.

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Say for example the A need class B okay.

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And class B also needs class A.

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This will create for you something called circular dependency.

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Let I write for you.

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For example we have a service A okay in the service A we inject the service B okay.

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And in the service B we also inject the service A.

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now you can see right here and right here it will create something called circular dependency.

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So Now, let me demonstrate this for you.

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Maybe in future we will.

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You will meet that.

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For example, I have a post and a user, right?

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For example.

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User.

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The user.

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Here I will inject the postService and inside the post right here I will also inject the the userService

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service

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Like that

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Now if I run the project.

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Actually I must write a private over here.

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Okay, now let's wait a bit.

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I think I will pause the video a little bit.

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Now we have something error.

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Like that

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Okay.

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If you can scroll down.

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And this error is not relate anything to the circular dependency.

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I just talk about that okay.

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This just we forgot to import the user module inside the post module right here.

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Okay.

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We must import the user module.

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Like that

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And inside the user service let me see sorry.

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Inside the user module we must export the UserService

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like that

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And actually if you not import it is already show the error right.

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But anyway let me remove and you can see it will say the error, something like circular dependency.

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Okay, now we can use the forwardRef to avoid the circular dependency.

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Let me show you the documentation now right here.

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For example, we have a cat service and we also have a common service.

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And now you can see in the common service, it use sorry.

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In the CatService, it's use the CommonService

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And also in the CommonService, it use the CatService

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Okay.

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This will create something called a circular dependency.

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And we can avoid that due to something called forwardRef with the inject annotation right here.

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Okay.

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You can test that I will not test right here also.

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And actually in here we have something called common module.

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We can use that-- right here, but.

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Let me tell you about a little bit in.

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We must avoid the circular dependency as we can.

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Okay.

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And in any programming language and any framework, we must avoid the circular dependency.

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Okay.

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So for that reason, if you have a circular dependency in our project and in your future project.

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Now let's think about us a little bit.

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Okay.

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Let's stop and think about that and try to avoid a circular dependency.

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So that's it. That's my advice and that's for the video.

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So I will see you in the next one.