Version Control System

A version control system (also known as a Revision Control System) is a repository of files, often the files for the source code of computer programs, with monitored access. Every change made to the source is tracked, along with who made the change, why they made it, and references to problems fixed, or enhancements introduced, by the change.

Version control systems are essential for any form of distributed, collaborative development. Whether it is the history of a wiki page or large software development project, the ability to track each change as it was made, and to reverse changes when necessary can make all the difference between a well managed and controlled process and an uncontrolled ‘first come, first served’ system. It can also serve as a mechanism for due diligence for software projects.

Subversion

Subversion is a version control system.. Subversion is used as a configuration management system to allow multiple users to develop on one project at the same time. Programmers can check out the latest version of the code from a repository, make their changes to the code, and then commit the files back to Subversion. Subversion keeps track of the changes and then integrates the changes back into the main code base or lets the programmer know if other modifications where made between their last download and subsequent upload.

Terminology used in Subversion

In the course of working on a project, a developer should work in the following manner. How to perform all of these task is outlined below.

If the project is new, the following is done the first time:

A developer checks in a project for the first time, putting all of the files on the repository.
Other developers check out the project into their workspace. If a developer changes workspaces, the code would need to be checked out again.

In the course of working, a developer should strictly follow these steps:

Update their code, to obtain any changes that others made
Work on their code
Periodically (about every half-hour to an hour), the developer should synchronize, which displays any recent changes to the repository and which local code has been changed (synchronize doesn't actually do anything, it just tells you what needs to be done).
If the developer has changed a file locally, and the files on the repository have been changed since the last update, a merge will need to take place

The developer commits his/her changes of the local code to the repository

Subclipse Vs Subversive

Subclipse and Sunversive, both are most popular Eclipse plug-in which provides the functionality to interact with a Subversion server, and to manipulate a project on a Subversion server in the Eclipse environment.

For more information about Subclipse here: http://subclipse.tigris.org/
For more information about Subversive here: http://www.eclipse.org/subversive/
Both seem to have the same functionalities, with Subclipse having the updated compare features. But Subeclipse Plugin-in is provided by the same people who develops Subversion (Tigris.org) so it’s most widely used.

Installing Subclipse Plug-in to Eclipse

Switch to the Java/Plug-in Development perspective. To disconnect a project from the repository,

right click on the project and select Team > Disconnect. Eclipse will prompt asking if you wish to

delete the metadata associated with the Subversion connection. Choose No. If you choose yes, you

will have to delete the project in your workspace in order to check out another copy of the code.

Note: You will rarely need this feature.

Pre-requisite: Assuming Eclipse is already installed on your OS.

You can add the Subclipse plug-in to Eclipse by creating an update site in Eclipse and download

and install Subclipse.

Create an update site for Subclipse

· Select Help > Software Updates > Find and Install. Select Search for new features to install.

Click Next.

· Click the New Remote Site button. Give the update site a name, like Subclipse, and type in the

following address: http://subclipse.tigris.org/update_1.8.x. Click OK. A new update site will be

added to the list.

· Press the + next to your Subclipse update site. Eclipse will connect with the site and list all of the

updates available.

· Select the most recent Subclipse update by checking the box next to the update. Click Next.

· Check the Subversion feature that you want to install. Click Next.

· Accept the terms of the license agreement. Click Next.

· Make sure that the Subversion feature is selected to install. Click Finish.

· You will be asked to verify the feature that you wish to install. After you have, click Install.

· You will now be asked to restart the workbench. Click Yes.

Subclipse Perspectives

Switch to the Java/Plug-in Development perspective. To disconnect a project from the repository,

right click on the project and select Team > Disconnect. Eclipse will prompt asking if you wish to

delete the metadata associated with the Subversion connection. Choose No. If you choose yes, you

will have to delete the project in your workspace in order to check out another copy of the code.

Note: You will rarely need this feature.

To change to the Subclipse perspective select Window > Open Perspective > Other... > SVN Repository

Exploring.

The SVN Repository Exploring gives you three new views: SVN Repository, SVN Annotate, and

SVN Resource History. The SVN Repository view lists all of the current repositories that you have

access to. You can also create a new SVN Repository. The SVN Annotate view shows the annotations

of a file in the repository.

In order to view the annotations of a file, you must right click on the file and select Team >

Show Annotations.

The last view, SVN Resource History, shows the revision history for a file that is selected

in the SVN Repository view.

Notation : New files or directory added shown as Question mark(?) and updated files are as

greyed asterisk(*)

Adding a Repository URL to Subclipse

Switch to the Java/Plug-in Development perspective. To disconnect a project from the repository,

right click on the project and select Team > Disconnect. Eclipse will prompt asking if you wish to

delete the metadata associated with the Subversion connection. Choose No. If you choose yes, you

will have to delete the project in your workspace in order to check out another copy of the code.

Note: You will rarely need this feature.

To add a repository you can right click in the SVN Repository view and select New > SVN Repository,

or you can click the add repository button in the toolbar of the SVN Repository view.

· First you need to fill out the URL for the repository.

· Provide your user id and password.

· Click Finish.

· Your repository will be located in the SVN Repository view.

Check In: Adding an Already Existing Project to the Repository

Switch to the Java/Plug-in Development perspective. To disconnect a project from the repository,

right click on the project and select Team > Disconnect. Eclipse will prompt asking if you wish to

delete the metadata associated with the Subversion connection. Choose No. If you choose yes, you

will have to delete the project in your workspace in order to check out another copy of the code.

Note: You will rarely need this feature.

Switch to the Java perspective or Java EE perspective where your project is located.

To add your project to the repository, right click on the project and select Team > Share Project....

Select SVN from the list of repository types. Click Next.

If the project had not been previously shared, Eclipse will ask if you would like to create a new

repository to share the project in or if you would like to use an already existent repository to

share the project in. Choose the repository that you have already created for your project and click Next.

Select the radio button that says Use project name as module name. You can choose to have other

module names if you are afraid of name space conflicts. Click Next.

Click Finish.

If the project has been previously shared, Eclipse will ask if you wish to connect. Click Finish.

By convention, a project should be located in the trunk/ directory of the repository, NOT in the root.

If an Eclipse project is in the repository (e.g. test-project), then the project should be in /trunk/test-project/.

Navigate to Team-Synchronization perspective to view the project. Always use this perspective to see local changes which are either not checked-in or committed. Here, you can see the list of files to be checked-in or to commit.

Check Out a Project from the Repository

Switch to the Java/Plug-in Development perspective. To disconnect a project from the repository,

right click on the project and select Team > Disconnect. Eclipse will prompt asking if you wish to

delete the metadata associated with the Subversion connection. Choose No. If you choose yes, you

will have to delete the project in your workspace in order to check out another copy of the code.

Note: You will rarely need this feature.

Switch to the SVN Repository Exploring perspective. Click the + next to your repository. To check out

a project right click on any folder/project and select Check Out as Project. If the project that you are

checking out already exists in the workspace, the old project will be destroyed and the project from

the SVN repository will be created in its place. Otherwise a new project will be created in the

workspace. Switch back to the Java or Plug-in Development perspective to modify the code.

Synchronizing and Committing Resources to the Repository

Switch to the Java/Plug-in Development perspective. To disconnect a project from the repository,

right click on the project and select Team > Disconnect. Eclipse will prompt asking if you wish to

delete the metadata associated with the Subversion connection. Choose No. If you choose yes, you

will have to delete the project in your workspace in order to check out another copy of the code.

Note: You will rarely need this feature.

Any resources that you have modified will have a black asterisk in front of the resource name, and

any added will have a question mark in front of the name.

It is always a good idea to see what needs to be done before committing files.

To synchronize resources, right click on a project and select Team > Synchronize with Repository ....

You will be switched to the Team Synchronizing view. From there you can look at your outgoing changes,

and others incoming changes, and synchronize your code before committing to the repository.

Double-clicking on a file will open a side-by-side view of the file and its changes.

If a file has a two-way red arrow on it, then there is a conflict. Someone else has changed that file

while you were working on it. Double-click the file to get a compare editor, and copy-paste what you

need to resolve onto your local copy. When you have the local copy finished, right-click on the file

and choose Mark as Merged.

Note: PLEASE USE THIS FEATURE RESPONSIBLY!!

Think very hard before selecting "Mark as Merged", as it will override what is in the repository. An entire

history is kept in case you make a mistake, but always pause and check your work before marking as

merged.

Note: constantly updating your code from the repository helps avoid conflicts

Synchronizing Resources

Switch to the Java/Plug-in Development perspective. To disconnect a project from the repository,

right click on the project and select Team > Disconnect. Eclipse will prompt asking if you wish to

delete the metadata associated with the Subversion connection. Choose No. If you choose yes, you

will have to delete the project in your workspace in order to check out another copy of the code.

Note: You will rarely need this feature.

To commit changes to files in your project, right click on the project and select Team > Commit....

Or, if your are in the "Team Synchronizing" perspective, right-click on the resources and select "Commit".

Then you will edit the commit comment, or add a new commit comment to document what changes

were made. Always add meaningful commit comments! There is also a list of previously used commit

comments to choose from. Once you have committed code, the black asterisk should be gone from

modified files.

History

To compare your code with the latest from the repository, you may either recheck out the project

or right click on the project in the Java/Plug-in Development perspectives and select Compare With >

Latest from repository. Using copy and paste, one can recover old code this way. Using Compare

With Revision... or Replace With Revision are also helpful.

Note: Always compare your file with latest from repository before commit.

Also, Team > Show History shows an entire history of a folder/file.

Disconnecting a Project from the Repository