Using git with multiple remote repositories

When one just isn’t good enough


Recently I was honored to be added to the taffydb maintainer list. This means I now need to merge changes from multiple remote repositories. Usually this can be done using the GitHub web interface but sometimes this is not flexible enough. Luckily, it’s rather easy to set up your git working directory to have a different remote repository for different branches and then merge between them. This post shows how.

Getting set up

Below I illustrate checking out taffydb on the master branch, and then set up two alternate branches using two different source repositories.

First, let’s get the canonical taffydb repository:

git clone taffydb

Now let’s enter that directory and have a look around:

cd taffydb
git remote -v
  # origin (fetch)
  # origin (push)

Let’s add our upstream branch to ltullman.

# create new branch
git checkout -b ltullman-master 

# add remote repository
git remote add ltullman

# fetch the master branch contents
git fetch ltullman master

# and now set upstream
git branch --set-upstream-to=ltullman/master

# confirm upstream branch
git rev-parse --abbrev-ref --symbolic-full-name @{u}
  # ltullman/master

# confirm origin
git remote -v
  # ltullman (fetch)
  # ltullman (push)
  # origin (fetch)
  # origin (push)

At this point, we have an ltullman-master that uses the ltullman upstream repository. Let’s add another:

git checkout master
git checkout -b mmikowski-master 
git remote add mmikowski 
git fetch mmikowski master
git branch --set-upstream-to=mmikowski/master

And confirm again:

git rev-parse --abbrev-ref --symbolic-full-name @{u}
  # mmikowski/master

git remote -v
  # ltullman (fetch)
  # ltullman (push)
  # mmikowski (fetch)
  # mmikowski (push)
  # origin (fetch)
  # origin (push)

Now we have all the sources we want. Now let’s explore what we can do!

What can we do with this?

I found that when setting up multiple upstream sources like this, we need to do a little work to get the branch to be “pristine”. For example, I found a merge conflict in my local copy of mmikowski-master. I wanted that fixed, and to match the upstream copy exactly. So I cloned another local copy and then made sure my mmikowski-master branch matched it exactly:

git checkout master-mmikowski
cd ..
git clone taffydb-mmikowski

# visual diff tool to merge remote master to local - copy all files
#  from source (left)
kdiff3 taffydb-mmikowski taffydb

# resolve conflicts
cd taffdb
git add .
git commit -a

# And push 
git push mmikowski HEAD:master

We can do the same check with ltullman. Now we can cherry-pick changes from a branch and merge them into master. In the example below, I merged over my regression tests but left other changes alone as I didn’t feel they were well-tested enough.

checkout master
git difftool mmikowski-master taffy-test.html

When to use this

Pull-requests that can be resolved from the GitHub web interface are always preferred if possible. However, sometimes circumstances require more nuanced merging, and this is where having remote repositories for each branch is very, very handy.

Cheers, Mike

Written on October 22, 2015