Add support for updating configuration options from environment variables.

Signed-off-by: Roberto Rosario <roberto.rosario.gonzalez@gmail.com>

HISTORY.rst

@@ -7,6 +7,7 @@ XX (2017-XX-XX)
 - Fix repeated permission list API URL. GitLab issue #389.
 - Fix role creation API endpoint not returning id. GitLab issue #390.
 - Make tags, metadata types and cabinets searchable via the dynamic search API. GitLab issue #344.
+- Add support for updating configuration options from environment variables.
 
 2.3 (2017-06-08)
 ================

docs/topics/settings.rst

@@ -10,3 +10,9 @@ the directory: ``/usr/share/mayan-edms/mayan/settings/local.py``.
 For a list of all the configuration options, go to "Setup" then "Settings" on
 your browser. This is also a good place to check if your overrided setting
 option value in your ``local.py`` file is being interpreted correctly.
+
+Settings can also be changed via environment variables by prepending the string
+"MAYAN_" to the configuration name. For example, to change the number of documents
+displayed per page (COMMON_PAGINATE_BY, by default 40), use::
+
+    MAYAN_COMMON_PAGINATE_BY=10

mayan/apps/smart_settings/classes.py

@@ -2,6 +2,7 @@ from __future__ import unicode_literals
 
 from importlib import import_module
 import logging
+import os
 
 import yaml
 
@@ -85,7 +86,11 @@ class Setting(object):
         return unicode(self.global_name)
 
     def cache_value(self):
-        self.raw_value = getattr(settings, self.global_name, self.default)
+        environment_value = os.environ.get('MAYAN_{}'.format(self.global_name))
+        if environment_value:
+            self.raw_value = yaml.safe_load(environment_value)
+        else:
+            self.raw_value = getattr(settings, self.global_name, self.default)
         self.yaml = Setting.serialize_value(self.raw_value)
         self.loaded = True