Externals Definitions
Sometimes it is useful to construct a working copy that is made out of a number of different checkouts. For example, you may want different subdirectories to come from different locations in a repository, or perhaps from different repositories altogether. You could certainly setup such a scenario by hand—using svn checkout to create the sort of nested working copy structure you are trying to achieve. But if this layout is important for everyone who uses your repository, every other user will need to perform the same checkout operations that you did.
Fortunately, Subversion provides support for externals definitions. An externals definition is a mapping of a local directory to the URL—and possibly a particular revision—of a versioned resource. In Subversion, you declare externals definitions in groups using the svn:externals property. You can create or modify this property using svn propset or svn propedit (see «Çà÷åì íóæíû ñâîéñòâà?»). It can be set on any versioned directory, and its value is a multi-line table of subdirectories (relative to the versioned directory on which the property is set) and fully qualified, absolute Subversion repository URLs.
$ svn propget svn:externals calc third-party/sounds http://sounds.red-bean.com/repos third-party/skins http://skins.red-bean.com/repositories/skinproj third-party/skins/toolkit -r21 http://svn.red-bean.com/repos/skin-makerThe convenience of the svn:externals property is that once it is set on a versioned directory, everyone who checks out a working copy with that directory also gets the benefit of the externals definition. In other words, once one person has made the effort to define those nested working copy checkouts, no one else has to bother—Subversion will, upon checkout of the original working copy, also checkout the external working copies.
Note the previous externals definition example. When someone checks out a working copy of the calc directory, Subversion also continues to checkout the items found in its externals definition.
$ svn checkout http://svn.example.com/repos/calc A calc A calc/Makefile A calc/integer.c A calc/button.c Checked out revision 148. Fetching external item into calc/third-party/sounds A calc/third-party/sounds/ding.ogg A calc/third-party/sounds/dong.ogg A calc/third-party/sounds/clang.ogg … A calc/third-party/sounds/bang.ogg A calc/third-party/sounds/twang.ogg Checked out revision 14. Fetching external item into calc/third-party/skins …If you need to change the externals definition, you can do so using the regular property modification subcommands. When you commit a change to the svn:externals property, Subversion will synchronize the checked-out items against the changed externals definition when you next run svn update. The same thing will happen when others update their working copies and receive your changes to the externals definition.
The svn status command also recognizes externals definitions, displaying a status code of X for the disjoint subdirectories into which externals are checked out, and then recursing into those subdirectories to display the status of the external items themselves.
