mgoeminne / scalagit

A simple binding for Git in Scala

scalagit

A simple binding for Git in Scala

Quickstart

$ git clone https://github.com/mgoeminne/scalagit.git ./scalagit
$ cd scalagit
$ sbt package

Getting started

This library can be used for querying a local Git repository. Currently, only read operations are allowed as scala-git is mainly used for analysis purpose. A recent version of Git needs to be installed in order to benefit from the services proposed by the library.

Git objects

The entry point of any analysis is the creation of an object representing the Git repository. This repository can be regular, in which case the directory containing the .git directory must be used. Bare repositories are also exploitable by using the X.git directory itself.

val repository = new Git(new File("/foo/bar/repos.git"))

Once such an object has been created, several methods can be used to list the commits, files and contributors involved in the repository.

import com.github.nscala_time.time.Imports._

val recent_commits = repository.commits.filter(c => c.date >= DateTime.now - 2.months)
val n_local_branches = repository.local_branches.size()
val committers = repository.commits.map(_.author).flatten

Commit and Blob objects

A commit object represents a commit and contains the most common values associated to it. In addition, the content associated to the commit can be obtained by invoking Commit::tree. The retrieved element is a tree, the nodes of which being either treenodes, or blobs. The blobs are elements representing the actual content of files existing in the considered commit.

The ancestors of the considered commit (if any), can be obtained by successively invoking the parents methods:

val commit = repository.commit.head
val is_merge_commit = commit.parents.size > 1

The list of all files associated to a commit, as well the blobs representing the content of these files, can also be directly accessed:

val commit = repository.commit.head
val file_blob = commit.existing_files
val files = commit.files
val blobs = commit.blobs

If the content stored in a blob is textual, its value can be retrieved as a character string.

val content = blob.lines 

Reverse and transversal methods

The library also includes some methods that allow the user to break the Git storage schema. You can for instance determine all the commits in which a given blob has been stored, or all the commits in which a file was present.

val f = blob.files.head
val commits = f.commits

These operations typically require a longer execution time, since the Git storage schema is not adapted for quickly answering the submitted queries, or because Git does not provide any tools for directly execute them, which forces scala-git to send multiple simpler queries to Git.

How does it work?

Scala-git is essentially a thin set of helpers for executing the Git executable. In some cases, it also manipulates the obtained results for presenting them in a format that facilitates further manipulations. That means that the obtained results may depend on the version of Git you installed on your computer (the Git API sometimes subtly changes over time).

It also means that Scala-git only exposes a subset of all the features provided by Git. In particular, no write operations are possible currently, and read operations mainly aim to provide a clear representation of a Git repository. Operations are added when I need them, so feel free to propose a patch for supporting your own required features.

Most operations retrieve stream of data, which allows you to only wait until Git retrieves the information you are interested in. Streams tend to minimize the overhead caused by the extra layer introduced by the library. However, no significant performance benchmark has been carried out so far for determining the importance of this overhead.

Licence

LGPL 3