Git Branching – Branches in a Nutshell

https://git-scm.com/book/en/v2/Git-Branching-Branches-in-a-Nutshell

3.1 Git Branching – Branches in a Nutshell

Nearly every VCS has some form of branching support. Branching means you diverge from the main line of development and continue to do work without messing with that main line. In many VCS tools, this is a somewhat expensive process, often requiring you to create a new copy of your source code directory, which can take a long time for large projects.

Some people refer to Git’s branching model as its “killer feature,” and it certainly sets Git apart in the VCS community. Why is it so special? The way Git branches is incredibly lightweight, making branching operations nearly instantaneous, and switching back and forth between branches generally just as fast. Unlike many other VCSs, Git encourages workflows that branch and merge often, even multiple times in a day. Understanding and mastering this feature gives you a powerful and unique tool and can entirely change the way that you develop.

Branches in a Nutshell

To really understand the way Git does branching, we need to take a step back and examine how Git stores its data.

As you may remember from Getting Started, Git doesn’t store data as a series of changesets or differences, but instead as a series of snapshots.

When you make a commit, Git stores a commit object that contains a pointer to the snapshot of the content you staged. This object also contains the author’s name and email address, the message that you typed, and pointers to the commit or commits that directly came before this commit (its parent or parents): zero parents for the initial commit, one parent for a normal commit, and multiple parents for a commit that results from a merge of two or more branches.

To visualize this, let’s assume that you have a directory containing three files, and you stage them all and commit. Staging the files computes a checksum for each one (the SHA-1 hash we mentioned in Getting Started), stores that version of the file in the Git repository (Git refers to them as blobs), and adds that checksum to the staging area:

$ git add README test.rb LICENSE

$ git commit -m ‘The initial commit of my project’

When you create the commit by running git commit, Git checksums each subdirectory (in this case, just the root project directory) and stores those tree objects in the Git repository. Git then creates a commit object that has the metadata and a pointer to the root project tree so it can re-create that snapshot when needed.

Your Git repository now contains five objects: three blobs (each representing the contents of one of the three files), one tree that lists the contents of the directory and specifies which file names are stored as which blobs, and one commit with the pointer to that root tree and all the commit metadata.

Figure 9. A commit and its tree

If you make some changes and commit again, the next commit stores a pointer to the commit that came immediately before it.

Figure 10. Commits and their parents

A branch in Git is simply a lightweight movable pointer to one of these commits. The default branch name in Git is master. As you start making commits, you’re given a master branch that points to the last commit you made. Every time you commit, the master branch pointer moves forward automatically.

Note The “master” branch in Git is not a special branch. It is exactly like any other branch. The only reason nearly every repository has one is that the git init command creates it by default and most people don’t bother to change it.

Figure 11. A branch and its commit history

Creating a New Branch

What happens when you create a new branch? Well, doing so creates a new pointer for you to move around. Let’s say you want to create a new branch called testing. You do this with the git branch command:

$ git branch testing

This creates a new pointer to the same commit you’re currently on.

Figure 12. Two branches pointing into the same series of commits

How does Git know what branch you’re currently on? It keeps a special pointer called HEAD. Note that this is a lot different than the concept of HEAD in other VCSs you may be used to, such as Subversion or CVS. In Git, this is a pointer to the local branch you’re currently on. In this case, you’re still on master. The git branch command only created a new branch — it didn’t switch to that branch.

Figure 13. HEAD pointing to a branch

You can easily see this by running a simple git log command that shows you where the branch pointers are pointing. This option is called –decorate.

$ git log –oneline –decorate

f30ab (HEAD -> master, testing) add feature #32 – ability to add new formats to the central interface

34ac2 Fixed bug #1328 – stack overflow under certain conditions

98ca9 The initial commit of my project

You can see the “master” and “testing” branches that are right there next to the f30ab commit.

Switching Branches

To switch to an existing branch, you run the git checkout command. Let’s switch to the new testing branch:

$ git checkout testing

This moves HEAD to point to the testing branch.

Figure 14. HEAD points to the current branch

What is the significance of that? Well, let’s do another commit:

$ vim test.rb

$ git commit -a -m ‘made a change’

Figure 15. The HEAD branch moves forward when a commit is made

This is interesting, because now your testing branch has moved forward, but your master branch still points to the commit you were on when you ran git checkout to switch branches. Let’s switch back to the master branch:

$ git checkout master

Figure 16. HEAD moves when you checkout

That command did two things. It moved the HEAD pointer back to point to the master branch, and it reverted the files in your working directory back to the snapshot that master points to. This also means the changes you make from this point forward will diverge from an older version of the project. It essentially rewinds the work you’ve done in your testing branch so you can go in a different direction.

Note Switching branches changes files in your working directory It’s important to note that when you switch branches in Git, files in your working directory will change. If you switch to an older branch, your working directory will be reverted to look like it did the last time you committed on that branch. If Git cannot do it cleanly, it will not let you switch at all.

Let’s make a few changes and commit again:

$ vim test.rb

$ git commit -a -m ‘made other changes’

Now your project history has diverged (see Divergent history). You created and switched to a branch, did some work on it, and then switched back to your main branch and did other work. Both of those changes are isolated in separate branches: you can switch back and forth between the branches and merge them together when you’re ready. And you did all that with simple branch, checkout, and commit commands.

Figure 17. Divergent history

You can also see this easily with the git log command. If you run git log –oneline –decorate –graph –all it will print out the history of your commits, showing where your branch pointers are and how your history has diverged.

$ git log –oneline –decorate –graph –all

* c2b9e (HEAD, master) made other changes

| * 87ab2 (testing) made a change

|/

* f30ab add feature #32 – ability to add new formats to the

* 34ac2 fixed bug #1328 – stack overflow under certain conditions

* 98ca9 initial commit of my project

Because a branch in Git is actually a simple file that contains the 40 character SHA-1 checksum of the commit it points to, branches are cheap to create and destroy. Creating a new branch is as quick and simple as writing 41 bytes to a file (40 characters and a newline).

This is in sharp contrast to the way most older VCS tools branch, which involves copying all of the project’s files into a second directory. This can take several seconds or even minutes, depending on the size of the project, whereas in Git the process is always instantaneous. Also, because we’re recording the parents when we commit, finding a proper merge base for merging is automatically done for us and is generally very easy to do. These features help encourage developers to create and use branches often. R

Unblock project files in Visual Studio

When you open a copy of project files from a remote location / downloaded from the internet you get the message that the project location is not trusted:

Unblock downloaded files in folder including subfolders:

gci -path “C:\BeeHive” -recurse | Unblock-File (replace “C:\BeeHive” with the folder in which you want to unblock all files)

How to develop with various app.config files

When I want to test my application in Microsoft Visual Studio I want to use a alternate app.config from production. In my development environment I have other connection strings etc.

To switch between development and production configuration I have come up with the following configuration:

I want to switch configuration in the IDE and use the apropriate app.config file.

For each environment I have added a separate app.config.file to my project.

Next I have added a pre-build.bat and a post-build.bat in the solution.

The pre-build.bat file contains one command to replace app.config for the selected configuration:

copy /y %1\app.config.%2 %1\app.config

The post-build.bat file contains one command to replace the app.config with the release or “production” configuration.

Last step is to tie these components all together. Add a Pre-build and a Post-build event in the project properties page. You should be able to find these settings right clicking the project and click on properties.

The command I added to start pre-build.bat is:

“$(ProjectDir)pre-build.bat” “$(ProjectDir)” “$(ConfigurationName)”

and for the post-build.bat the command is:

“$(ProjectDir)post-build.bat” “$(ProjectDir)”

Continuously Deploy Your ClickOnce Application From Your Build Server

http://blog.danskingdom.com/continuously-deploy-your-clickonce-application-from-your-build-server/ from Daniel Schroeder’s (aka deadlydog) Programming Blog

ClickOnce applications are a great and easy way to distribute your applications to many users, and have the advantage of offering automatic application updates out-of-the-box. Even though ClickOnce applications are super easy to deploy from Visual Studio (literally 3 clicks, just click Build –> Publish –> Finish), you may still want to have your build system publish the updates for various reasons, such as:

You don’t want you (or your team members) to have to remember to manually publish a new version all the time; even if it is very quick and easy.

If you are signing your ClickOnce application (to make your app more secure and avoid annoying Windows security warnings during every update), your team members may not have the certificate installed, or you may not want them to know the certificate password.

All of the other benefits of deploying automatically from a build server; you can be sure the project was built in Release mode, all unit tests have run and passed, you are only publishing a new version of the application from a specific branch (e.g. master), etc.

In this post I’m going to show how to continuously deploy your ClickOnce application using Visual Studio Team Services (VSTS), but you can adopt what’s shown here to work on any build system, such as Team City or Jenkins.

Step 1 – Configure and publish your ClickOnce application manually

Before we can publish a new version of the application from the build server, we first have to build the project to create the artifacts to publish. And even before that, we have to make sure the project is setup properly with all of the required ClickOnce metadata. You will typically do this by going into your project Properties page and going to the Publish tab. There are several other websites and blog posts that discuss configuring a project for ClickOnce deployment, including the official MSDN documentation for configuring and publishing ClickOnce applications, so I won’t go into it any further here.

Basically you should have your project in a state where you can easily publish a new version manually, and it is configured the way that you want (includes the necessary files, has the destination to publish to specified, specifies if the application is only available online or not, etc.). Once you’ve published your project manually and confirmed that it’s configured the way you like, we can move onto the next step.

Step 2 – Setup the build on your build server

On your build server you will want to configure a new vanilla build that builds your project/solution. There are a couple modifications you will need to make that are different from building a regular console app or class library project.

The first difference is that you will need to provide the “/target:Publish” argument to MSBuild when it builds your project. Here is what this looks like in VSTS:

This will cause MSBuild to build the required artifacts into an “app.publish” directory. e.g. bin\Debug\app.publish.

The next difference is that you will want to copy that “app.publish” directory to your build artifacts directory. To do this, you will need to add a Copy Files step into your build process that copies the “app.publish” directory from the ClickOnce project’s bin directory to where the build artifacts are expected to be. You will want to do this before the step that publishes your build artifacts. Here is what this looks like in VSTS:

So we copy the files into the build artifacts directory, and then the Publish Build Artifacts step at the end will copy those files to wherever you’ve specified; in my case it’s a network share.

If you like you can now run the build and see if it succeeds. If the build fails with an error relating to an expired certificate or pfx file, see my other blog post on importing the required certificate on the build server at build-time, which involves adding one more “Import-PfxCertificate.ps1” build step before the MSBuild step.

For completeness sake, this is what my Publish Build Artifacts step looks like in VSTS, and you’ll also notice the “Import-PfxCertificate.ps1” step before the MSBuild step as well:

So we now have the ClickOnce artifacts being generated and stored in the appropriate directory. If you wanted, you could publish the build artifacts to the ClickOnce application’s final destination right now (instead of a file share as I’ve done here), but I’m going to follow best practices and separate the application “build” and “deployment” portions into their respective subsystems, as you may want separate control over when a build gets published, or maybe you don’t want to publish EVERY build; only some of them.

Hopefully at this point you are able to create a successful build, but we’re not done yet.

 Step 3 – Publish the build artifacts to the ClickOnce application’s destination

Now that we have the build artifacts safely stored, we can publish them to the ClickOnce application’s destination. With VSTS this is done by using the Release subsystem. So create a new Release Definition and setup an Environment for it. By default it adds a “Copy and Publish Build Artifacts” step to the release definition. When configuring and using this default step, I received the error:

[error]Copy and Publish Build Artifacts task is not supported within Release

So instead I removed that default step and added a simple “Copy Files” step, and then configured it to grab the files from the file share that the build published the artifacts to, and set the destination to where the ClickOnce application was publishing to when I would do a manual publish from within Visual Studio. Here is what that step looks like in VSTS:

You should be able to run this release definition and see that it is able to post a new version of your ClickOnce application. Hooray! I setup my releases to automatically publish on every build, but you can configure yours however you like.

If you make changes and commit them, the build should create new artifacts, and the release should be able to publish the new version. However, if you launch your ClickOnce application, you may be surprised that it doesn’t actually update to the latest version that you just committed and published. This is because we need one additional build step to actually update the ClickOnce version so it can detect that a new version was published. If you launch another build and publish them, you’ll see that the files being published are overwriting the previous files, instead of getting published to a new directory as they are supposed to be.

You may be wondering why we need another build step to update the ClickOnce version. Part of the build artifacts that are created are a .application manifest file, and a directory that contains the applications files, both of which have the ClickOnce version in them. Can’t we just modify the directory name and .application manifest file to increment the old version number? This was my initial thought, but the .application manifest file contains a cryptography hash to ensure that nobody has tampered with it, meaning that it needs to contain the proper version number at the time that it is generated.

Step 4 – One more build step to update the ClickOnce version

The ClickOnce version is defined in your project file (.csproj/.vbproj) (as the <ApplicationVersion> and <ApplicationRevision> xml elements), and is different from the assembly version that you would typically set to version your .dll/.exe files via the AssemblyInfo.cs file. Unless you manually updated the ClickOnce version in Visual Studio, it will still have its original version. When publishing the ClickOnce version in Visual Studio, Visual Studio automatically takes care of incrementing ClickOnce version’s Revision part. However, because we’re publishing from our build system now, we’ll need to come up with an alternative method. To help solve this problem, I have created the Set-ProjectFilesClickOnceVersion GitHub repository. This repository houses a single Set-ProjectFilesClickOnceVersion.ps1 PowerShell script that we will want to download and add into our build process.

In order for the build system to access this Set-ProjectFilesClickOnceVersion.ps1 script you will need to check it into source control. Also, you need to make sure you add this build step before the MSBuild step. Here is what this step looks like in VSTS:

The Script Filename points to the location of the Set-ProjectFilesClickOnceVersion.ps1 script in my repository. Also note that I set the Working Folder to the directory that contains the .csproj project file. This is necessary since we are dealing with relative paths, not absolute ones.

For the Arguments I provide the name of the project file that corresponds to my ClickOnce application, as well as the VSTS Build ID. The Build ID is a globally unique ID that gets auto-incremented with every build, and most (all?) build systems have this. The script will translate this Build ID into the Build and Revision version number parts to use for the ClickOnce version, to ensure that they are always increasing in value. So you should never need to manually modify the ClickOnce version, and every build should generate a version number greater than the last, allowing the ClickOnce application to properly detect when a newer version has been published.

Maybe you update your application’s version number on every build, and want your ClickOnce version to match that version. If this is the case, then use the –Version parameter instead of –BuildSystemsBuildId. The other alternative is to use the –IncrementProjectFilesRevision switch to simply increment the ClickOnce Revision that is already stored in the project file. If you use this switch, you need to be sure to check the project file back into source control so that the Revision is properly incremented again on subsequent builds. I like to avoid my build system checking files into source control wherever possible, so I have opted for the BuildSystemsBuildId parameter here.

The last argument I have included is the UpdateMinimumRequiredVersionToCurrentVersion parameter, and it is optional. If provided, this parameter will change the ClickOnce application’s Minimum Required Version to be the same as the new version, forcing the application to always update to the latest version when it detects that an update is available. I typically use this setting for all of my ClickOnce applications. If you still plan on publishing your ClickOnce applications from Visual Studio, but want this functionality, simply install the AutoUpdateProjectsMinimumRequiredClickOnceVersion NuGet Package.

That’s it! Now if you launch another build it should create new artifacts with a larger ClickOnce version number, and once published your application should update to the new version.

 

Bonus – Displaying the ClickOnce version in your application

The ClickOnce application version number may be different than your assembly version number, or perhaps you don’t update your product’s version number on every publish; it’s easy to forget. I typically like to use semantic versioning for my projects, which only involves the first 3 version parts. This leaves the last version part, the Revision number, available for me to set as I please. I will typically use the ClickOnce Revision in my application’s displayed version number. This makes it easy to tell which actual release a client has installed in the event that the product version was not updated between releases. The code to do it is fairly simple.

public Version ApplicationVersion = new Version(“1.11.2”);
private void MainWindow_Loaded(object sender, RoutedEventArgs e)
{
// If this is a ClickOnce deployment, append the ClickOnce Revision to the version number (as it gets updated with each publish).
if (ApplicationDeployment.IsNetworkDeployed)
ApplicationVersion = new Version(ApplicationVersion.Major, ApplicationVersion.Minor, ApplicationVersion.Build,
ApplicationDeployment.CurrentDeployment.CurrentVersion.Revision);
// Display the Version as part of the window title.
wndMainWindow.Title += ApplicationVersion;
}

Here I hard-code the product version that I want displayed in my application in a variable called ApplicationVersion. When the WPF application is launched, I obtain the ClickOnce Revision and append it onto the end of the version number. I then display the version in my application’s window title, but you might want to show it somewhere else, such as in an About window. If you want, you could even display both the full application version and full ClickOnce version.