Intermediate commit with quite some progress in order to put all extra methods on the default Repo implementation into interfaces or something that can be abstracted. It shows that it would indeed be good to keep the differentiation between Repositories which contain an object database as it is clearly easier to setup any combination of repositories that use git and those that do not, with just the addition of one more level of indirection. Lets see how it will end up

1 files changed, 73 insertions, 1 deletions

diff --git a/git/db/py/base.py b/git/db/py/base.py
index f45711d5..cc326c27 100644
--- a/git/db/py/base.py
+++ b/git/db/py/base.py
@@ -35,7 +35,7 @@ import os
 
 
 __all__ = (	'PureObjectDBR', 'PureObjectDBW', 'PureRootPathDB', 'PureCompoundDB', 
-			'PureConfigurationMixin', 'PureRepositoryPathsMixin')
+			'PureConfigurationMixin', 'PureRepositoryPathsMixin', 'PureAlternatesFileMixin')
 
 
 class PureObjectDBR(ObjectDBR):
@@ -385,3 +385,75 @@ class PureConfigurationMixin(ConfigurationMixin):
 	
 	#} END interface
 	
+	
+class PureAlternatesFileMixin(object):
+	"""Utility able to read and write an alternates file through the alternates property
+	It needs to be part of a type with the git_dir or db_path property.
+	
+	The file by default is assumed to be located at the default location as imposed
+	by the standard git repository layout"""
+	
+	#{ Configuration
+	alternates_filepath = os.path.join('info', 'alternates')	# relative path to alternates file
+	
+	#} END configuration
+	
+	def __init__(self, *args, **kwargs):
+		super(PureAlternatesFileMixin, self).__init__(*args, **kwargs)
+		self._alternates_path()	# throws on incompatible type
+	
+	#{ Interface 
+	
+	def _alternates_path(self):
+		if hasattr(self, 'git_dir'):
+			return join(self.git_dir, 'objects', self.alternates_filepath)
+		elif hasattr(self, 'db_path'):
+			return self.db_path(self.alternates_filepath)
+		else:
+			raise AssertionError("This mixin requires a parent type with either the git_dir property or db_path method")
+		#END handle path
+	
+	def _get_alternates(self):
+		"""The list of alternates for this repo from which objects can be retrieved
+
+		:return: list of strings being pathnames of alternates"""
+		alternates_path = self._alternates_path()
+
+		if os.path.exists(alternates_path):
+			try:
+				f = open(alternates_path)
+				alts = f.read()
+			finally:
+				f.close()
+			return alts.strip().splitlines()
+		else:
+			return list()
+		# END handle path exists
+
+	def _set_alternates(self, alts):
+		"""Sets the alternates
+
+		:parm alts:
+			is the array of string paths representing the alternates at which 
+			git should look for objects, i.e. /home/user/repo/.git/objects
+
+		:raise NoSuchPathError:
+		:note:
+			The method does not check for the existance of the paths in alts
+			as the caller is responsible."""
+		alternates_path = self._alternates_path() 
+		if not alts:
+			if isfile(alternates_path):
+				os.remove(alternates_path)
+		else:
+			try:
+				f = open(alternates_path, 'w')
+				f.write("\n".join(alts))
+			finally:
+				f.close()
+			# END file handling 
+		# END alts handling
+
+	alternates = property(_get_alternates, _set_alternates, doc="Retrieve a list of alternates paths or set a list paths to be used as alternates")
+	
+	#} END interface