WEBVTT

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Hi everyone!

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In previous video we already know how to create a controller, right?

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And in this video, let me tell you the concept of solid principle and only the "s" of the solid principle

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will be the single responsibility.

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Now, before showing you what is the single responsibility, let me click on the app.controllers.

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dot ts

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Right here, you can see in the get hello right here, it use the something call "service" to get the hello.

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Why it's use something like this.

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Okay.

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Instead of write directly hello world right here.

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And it's also work.

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You can see, okay, but why?

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Why it use the service to get?

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Hello.

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Okay.

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Well, with the concept of single responsibility.

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The single responsibility means one class only responsible zero for one purpose.

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Now, what does it mean?

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Firstly, we have a three class.

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Okay.

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Actually, in here it's don't have a "repository", but I will discuss that.

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Don't worry about that.

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Firstly, we have a controller.

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What is the purpose of the controller class right here?

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This will return data or the view

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Okay.

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It handles incoming requests and respond data.

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That's the whole purpose of controller.

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And what is the service?

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The service.

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It will handle the business logic.

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Right now we do not understand what is the business logic.

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We will progress in this course.

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Don't worry about that.

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And repository

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The repository is usually handle the database logic.

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If you say okay, you handle the underlying resource logic like database or file system okay.

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And with the controller we will usually call the service, and service

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We will call the repository and repository.

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Later it will return the data for the service and the service.

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It will handle the business.

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Okay.

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And it will return the data back to the controller.

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Okay.

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And the controller, it will return to the end user.

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And that's the concept of single responsibility.

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Okay.

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And let me write a little bit what is responsibility, right here in the controller.

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I will create one more.

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One more class test dot.

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Service dot.

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ts

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Okay.

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Right here we have a service.

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Right.

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In order to give the test service, firstly, I will create a test service first

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And for example, I will have a get method.

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I have a method.

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Sorry.

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Let me see add number, for example.

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In the add number right here or I will say add and I will return the one plus one plus, for example

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like this.

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And I will export class and we sorry we don't have a bracket right here.

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And the error right here.

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Let's quickly fix that

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Let's click on CLRF right here and change to LF.

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I will fix that later.

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We have a service.

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Now let's see how we can use the service inside the controller.

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Okay.

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In order to use the service right here, we will init the service.

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Let me say, for example, I will create a private method with that service.

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And this is the test service right.

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And I will init it with new test service.

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Okay.

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And right here instead of return the file, actually I will create one more controller will be calculation.

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And right here we will call and I will return.

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this.testService.add()

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Now, if I go to the /calc, let's see what happened.

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/calc

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Okay, this will be the two, right?

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This is the idea of the service and what's in the repository.

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For example, I will create a test.repository.ts

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I will export class.

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Test repository

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And the repository right here.

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It will work with the database.

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Right.

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For example.

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I will get number in database.

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Okay.

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We have method like this, and in here I will return.

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For example I will have a data in database.

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Okay.

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For now I will fix the code like this.

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And I will return the data in DB okay.

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In later we will get the data in the real database.

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But for now let's ignore that and let's assume this is the operation from database.

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Okay.

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We have a data in database.

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We will return this right.

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And let me fix that.

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And inside the service, instead of using here, I will call the private test

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repository

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test repository

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Okay.

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And instead of using here, I will call the test this.testRepo.getNumber and I will plus

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it with one.

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Now if I refresh it will work, right?

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And that's the concept of single responsibility in the controller.

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We will call the service.

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And in the service we will call the repository.

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And we will return back the data for the service.

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Okay.

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And from service we will return back data for the controller.

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And for that reason we will see the data right here.

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Okay.

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That's it for the video.

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I will see you in the next one.