Exercise - Push a change through the pipeline

19 minutes

In this unit, you'll practice the complete code workflow by pushing a small change to the Space Game website to GitHub.

Mara has been given the task of changing some text on the home page of the website, Index.cshtml. In this unit, you'll follow along.

Let's briefly review the steps to follow to complete the task:

Synchronize your local repository with the latest main branch on GitHub.
Create a branch to hold your changes.
Make the code changes you need, and verify them locally.
Push your branch to GitHub.
Merge any recent changes from the main branch on GitHub into your local working branch, and verify that your changes still work.
Push up any remaining changes, watch Azure Pipelines build the application, and submit your pull request.

Fetch the latest main branch

In the previous unit, you created a pull request and merged your code-workflow branch into the main branch on GitHub. Now you need to pull the changes to main back to your local branch.

The git pull command fetches the latest code from the remote repository and merges it into your local repository. This way, you know you're working with the latest code base.

In your terminal, run git checkout main to switch to the main branch:
```
git checkout main
```
To pull down the latest changes, run this git pull command:
```
git pull origin main
```
You can view the list of files that were changed. As an optional step, you can open the azure-pipelines.yml file to verify that it contains your complete build configuration.

Recall that a Git repository where team members collaborate (such as on GitHub) is called a remote. Here, origin specifies your repository on GitHub.

Later, you'll fetch starter code from the Microsoft GitHub repository, known as upstream.

Build and run the web application

To ensure that you have a working copy to start your changes, build and run the web application locally.

In Visual Studio Code, go to the terminal window and run the following dotnet build command to build the application:
```
dotnet build --configuration Release
```
Run the following dotnet run command to run the application:
```
dotnet run --configuration Release --no-build --project Tailspin.SpaceGame.Web
```
Tip

If you see an error in your browser that's related to a privacy or certificate error, select Ctrl+C from your terminal to stop the running application.

Then run dotnet dev-certs https --trust and select Yes when prompted, or see this blog post for more information.

After your computer trusts your local SSL certificate, run the dotnet run command a second time and go to http://localhost:5000 from a new browser tab to see the running application.

Verify that the application is running

In development mode, the Space Game website is configured to run on port 5000.

In a new browser tab, navigate to http://localhost:5000 to see the running application.

You should see this:

Screenshot of the Space Game website running in a web browser.

You can interact with the page, including the leaderboard. When you select a player's name, you see details about that player.

When you're finished, return to the terminal window, and select Ctrl+C to stop the running application.

Create a feature branch

In this section, you'll create a Git branch so that you can work on files without affecting anyone else. No one will even know you're working on those files until you push them to the remote repository.

To create a branch, you use the git checkout command and give your branch a name, just like you did in the previous part.

Before you create a branch, it's a good idea to adhere to a naming convention. For example, if your branch is for working on a new feature, you might use feature/<branch-name>. For a bug fix, you could use bugfix/<bug-number>. In this example, your branch name will be feature/home-page-text.

In your terminal, run the following git checkout command:

git checkout -B feature/home-page-text

Like before, the feature/home-page-text is based on the main branch.

Make changes and test it locally

In Visual Studio Code, open Index.cshtml in the Tailspin.SpaceGame.Web/Views/Home directory.
Look for this text near the top of the page:
```
<p>An example site for learning</p>
```
Tip

Visual Studio Code also provides an easy way to search for text in files. To access the search pane, select the magnifying glass icon in the side pane.
Replace the text in the previous step with the following "mistyped" text, and then save the file:
```
<p>Welcome to the oficial Space Game site!</p>
```
Note that the word "oficial" is intentionally mistyped. We'll address that error later in this module.
In your terminal, run the following dotnet build command to build the application:
```
dotnet build --configuration Release
```

Run the following dotnet run command to run the application:

dotnet run --configuration Release --no-build --project Tailspin.SpaceGame.Web

On a new browser tab, go to http://localhost:5000 to see the running application.

You can see that the home page contains the updated text.

When you're finished, return to the terminal window, and then press Ctrl+C to stop the running application.

Commit and push your branch

Here you'll stage your changes to Index.cshtml, commit the change to your branch, and push your branch up to GitHub.

Run git status to check and see whether there are uncommitted changes on your branch:
```
git status
```
You'll see that Index.cshtml has been modified. Like before, the next step is to make sure that Git is tracking this file, which is called staging the file.

Run the following git add command to stage Index.cshtml:

git add Tailspin.SpaceGame.Web/Views/Home/Index.cshtml

Run the following git commit command to commit your staged file to the feature/home-page-text branch:
```
git commit -m "Improve the text at the top of the home page"
```
Run this git push command to push, or upload, the feature/home-page-text branch to your repository on GitHub:
```
git push origin feature/home-page-text
```
Just as before, you can locate your branch on GitHub from the branch drop-down box.

Watch Azure Pipelines build the application

Just as you did previously, Azure Pipelines automatically queues the build when you push changes to GitHub.

As an optional step, trace the build as it moves through the pipeline, and verify that the build succeeds.

Synchronize any changes to the main branch

While you were busy working on your feature, changes might have been made to the remote main branch. Before you create a pull request, it's common practice to get the latest from the remote main branch.

To do this, first check out, or switch to, the main branch. Then, merge the remote main branch with your local main branch.

Next, check out your feature branch, and then merge your feature branch with the main branch.

Let's try the process now.

In your terminal, run this git checkout command to check out the main branch:
```
git checkout main
```
To download the latest changes to the remote main branch and merge those changes into your local main branch, run this git pull command:
```
git pull origin main
```
Because no one actually made any changes to your main branch, the following command tells you that everything is already up to date.
```
From https://github.com/username/mslearn-tailspin-spacegame-web
 * branch            main     -> FETCH_HEAD
Already up to date.
```
To check out your feature branch, run git checkout:
```
git checkout feature/home-page-text
```
Merge your feature branch with main:
```
git merge main
```
Again, because no one actually made any changes to your main branch, you see that everything is still up to date.
```
Already up to date.
```
If you did incorporate any changes, you would want to test your application again to ensure that everything is still working.

Push your local branch again

When you incorporate changes from the remote repository into your local feature branch, you need to push your local branch back to the remote repository a second time.

Although you didn't incorporate any changes from the remote repository, let's practice the process to see what happens.

Run this git push command to push your changes to GitHub:
```
git push origin feature/home-page-text
```
Once again, the response says that you're already up to date since no changes were made.
```
Everything up-to-date
```

Submit a pull request

In this section, you submit a pull request just as you did previously.

In a browser, sign in to GitHub.
Go to your mslearn-tailspin-spacegame-web repository.
In the drop-down list, select your feature/home-page-text branch.
To start your pull request, select Contribute and then Open pull request.
Ensure that the base drop-down list specifies your repository and not the Microsoft repository.

Important

Again, this step is important because you can't merge your changes into the Microsoft repository.

When you work directly with your own repository, and not a fork, your main branch is selected by default.
Enter a title and a description for your pull request.
- Title: Improve the text at the top of the home page
- Description: Received the latest home page text from the product team.
To complete your pull request, select Create pull request.

This step doesn't merge any code. It tells others that you have changes that you're proposing to merge.

The pull request window is displayed. As before, a pull request triggers Azure Pipelines to build your application by default.
Optionally, select the Details link or go to your project on Azure DevOps and watch the pipeline run.
When the build is finished, go back to your pull request on GitHub.
Select Merge pull request, and then select Confirm merge.
Select Delete branch to delete the feature/home-page-text branch from GitHub.

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