Skip to main content

Syncing your Git repo with the Subversion repo

This post is part of a series on Git and Subversion. To see all the related posts, screencasts and other resources, please click here

This is a follow-up to the previous post on how to live with Git and Suversion in parallel. It's really trivial stuff for any experienced user, but was worth noting down somewhere for my own sake.

I've cloned a project called "fudge" from Subversion:

>git svn clone https://scm.mycompany.com/svn/fudge

So my local repo has the correct svn-remote configuration and all that to go with it inside fudge/.git/svn. This is done automatically when you svn-clone.

The bad thing is that all my Git-mates at work have to wait for me doing svn-rebase before they can pull the latest code from Subversion from my repo into theirs.

I want to get rid of this responsibility. I'll put something similar to my svn-rebasing repository on a server, have it run svn-rebase regularly, and push the changes to a centralized git repository, that everyone can pull from whenever they want. Here's how:

First, I'll init a repo on the build server called "builder". It has a designated place for the git repos in the directory /scm/git/

>cd /scm/git
>git init --bare fudge.git

The --bare means a git repo with no local checkout, i.e. just the compressed stuff inside .git.


Back on my own machine, I register the above repo as a remote for my own. I'll call it origin (this may sound confusing as my local repo is actually the origin here, but it's kind of a git convention to name the centralized repo like that):

>git remote add origin ssh://[email protected]/scm/git/fudge.git

The above should add the following to my fudge/.git/config:

[remote "origin"]
fetch = +refs/heads/*:refs/remotes/origin/*
url = ssh://[email protected]/git/java/ips.git

Now, I can push my local repository to the build server. I have to specify which branch in the remote repo I'll push to (master oughta work):

>git push origin master

So, centralized repo is ready. Now, we want a second repository on builder that can do the svn-rebase action. You could probably do this in the same repo as the first one, but I think it's cleaner to do it separately. Besides, in order for svn-rebase to work, you need to have a repo with a local checkout.

We'll create this repo just like any other developer would: By cloning from the central repo (still on builder). I'll pretend there's a user on builder called "worker" designated for this kind of action:

cd /home/worker/projects
git clone /scm/git/fudge

If we try just running svn-rebase right away, something like this might happen:

>cd fudge
>git svn rebase
Migrating from a git-svn v1 layout...
Data from a previous version of git-svn exists, but
.git/svn
(required for this version (1.7.1) of git-svn) does not exist.
Done migrating from a git-svn v1 layout
Unable to determine upstream SVN information from working tree history

You'll see that Git created the .git/svn/refs/remotes/git-svn/  folder on its own, but there's not much in there. We have to make the repo aware of the remote Subversion repo in two steps:

First, copy the svn-remote config from your original repo (the one you svn cloned) .git/config into the worker's config:

[svn-remote "svn"]
url = https://scm.mycompany.com/svn/fudge
fetch = :refs/remotes/git-svn


While imagination would allow us to think that git-svn now could figure out the rest by itself, we still need to add a pointer to the git-svn remote. Look inside the original repo's references, and you should find a file .git/refs/remotes/git-svn with a SHA in it. You have to copy this file into the worker's repo as well (or just paste the SHA into a new file with that name).

Now, try svn-rebase again:

>git svn rebase
Rebuilding .git/svn/refs/remotes/git-svn/.rev_map.901b3fc1-1df5-aa1e-233f-0cced8b7b346 ...
r123 = 38aada9c84fdb74f2271706c2a4be768334b0cc1
....
Done rebuilding .git/svn/refs/remotes/git-svn/.rev_map.901b3fc1-1df5-aa1e-233f-0cced8b7b346
Current branch master is up to date.

That's it! So, let's recap what we had to do:
  1. Create a central repo (bare)
  2. Clone the repo 
  3. Add the svn-remote to .git/config
  4. Add a pointer/SHA in .git/refs/remotes/git-svn
Now, we can set up a process that regularly does svn rebase and svn push to have it continuously update the central repo with the latest changes from Subversion. You can do it in your CI-server, as a cron-job, or maybe trigger it with a Subversion post-commit hook.

Note: When you go back to work and want to push commits back to the Subversion repo, you have to use git svn dcommit. Pushing your changes to a central git repo and then having some automated job dcommitting back is a bad idea, I think. Please let me know if you any thoughts on what workflow to use, especially when multiple people are working with Git/Subversion repos.

Popular posts from this blog

Encrypting and Decrypting with Spring

I was recently working with protecting some sensitive data in a typical Java application with a database underneath. We convert the data on its way out of the application using Spring Security Crypto Utilities. It "was decided" that we'd be doing AES with a key-length of 256, and this just happens to be the kind of encryption Spring crypto does out of the box. Sweet!

The big aber is that whatever JRE is running the application has to be patched with Oracle's JCE in order to do 256 bits. It's a fascinating story, the short version being that U.S. companies are restricted from exporting various encryption algorithms to certain countries, and some countries are restricted from importing them.

Once I had patched my JRE with the JCE, I found it fascinating how straight forward it was to encrypt and decrypt using the Spring Encryptors. So just for fun at the weekend, I threw together a little desktop app that will encrypt and decrypt stuff for the given password and sa…

Managing dot-files with vcsh and myrepos

Say I want to get my dot-files out on a new computer. Here's what I do:

# install vcsh & myrepos via apt/brew/etc
vcsh clone https://github.com/tfnico/config-mr.git mr
mr update

Done! All dot-files are ready to use and in place. No deploy command, no linking up symlinks to the files. No checking/out in my entire home directory as a Git repository. Yet, all my dot-files are neatly kept in fine-grained repositories, and any changes I make are immediately ready to be committed:

config-atom.git
    -> ~/.atom/*

config-mr.git
    -> ~/.mrconfig
    -> ~/.config/mr/*

config-tmuxinator.git  
    -> ~/.tmuxinator/*

config-vim.git
    -> ~/.vimrc
    -> ~/.vim/*

config-bin.git   
    -> ~/bin/*

config-git.git          
    -> ~/.gitconfig

config-tmux.git  
    -> ~/.tmux.conf    

config-zsh.git
    -> ~/.zshrc

How can this be? The key here is to use vcsh to keep track of your dot-files, and its partner myrepos/mr for operating on many repositories at the same time.

I discovere…

Always use git-svn with --prefix

TLDR: I've recently been forced back into using git-svn, and while I was at it, I noticed that git-svn generally behaves a lot better when it is initialized using the --prefix option.

Frankly, I can't see any reason why you would ever want to use git-svn without --prefix. It even added some major simplifications to my old git-svn mirror setup.

Update: Some of the advantages of this solution will disappear in newer versions of Git.

For example, make a standard-layout svn clone:

$ git svn clone -s https://svn.company.com/repos/project-foo/

You'll get this .git/config:

[svn-remote "svn"]
        url = https://svn.company.com/repos/
        fetch = project-foo/trunk:refs/remotes/trunk
        branches = project-foo/branches/*:refs/remotes/*
        tags = project-foo/tags/*:refs/remotes/tags/*

And the remote branches looks like this (git branch -a):
    remotes/trunk
    remotes/feat-bar

(Compared to regular remote branches, they look very odd because there is no remote name i…

Considerations for JavaScript in Modern (2013) Java/Maven Projects

Disclaimer: I'm a Java developer, not a JavaScript developer. This is just what I've picked up the last years plus a little research the last days. It's just a snapshot of my current knowledge and opinions on the day of writing, apt to change over the next weeks/months.

We've gone all modern in our web applications, doing MVC on the client side with AngularJS or Ember, building single-page webapps with REST backends. But how are we managing the growing amount of JavaScript in our application?
You ain't in Kansas anymore So far we've just been doing half-random stuff. We download some version of a library and throw it into our src/main/webapp/js/lib, or we use it from a CDN, which may be down or unreachable when we want to use the application..

Some times the JS is minified, other times it's not. Some times we name the file with version number, other times without. Some times we get the latest library of master branch and name it with the commit-id in the fi…

Microsoft ups their Git efforts another notch

This week Microsoft announced first class Git support embedded in the coming version of Visual Studio.

Now, it's not completely shocking. We could have seen it coming since Microsoft started offering Git repos on CodePlex, and more recently offering a Git client for TFS. In any case, these are some big news. Scott Hanselman weighs on some features and some more background here.

For those who are a bit unaware of what the Git situation on Windows looks like these days, I've dotted down these notes:
Some explanation on these:

msysGit has long been The Way to use Git on Windows. It's basically a port of Git itself, so it's a command-line tool.GitExtensions (includes Visual Studio integration), TortoiseGit, Git Shell, posh-git and most other tools are powered by msysGit.libgit2 is a native library for doing Git stuff. It is developed completely separate from Git itself. The above tools could (and should) probably use libgit2 instead of hooking onto and around msysGit.Github…