185 The `config` variable is an object which can be used to access the

   186 configuration values, for reading and updating, with a dictionary-like

   187 syntax. 

   188 

   189 Example 1: migration script changing the variable 'sender-addr' in

   190 all-in-one.conf. The script also checks that in that the instance is

   191 configured with a known value for that variable, and only updates the

   192 value in that case.

   193 

   194 .. sourcecode:: python

   195 

   196  wrong_addr = 'cubicweb@loiglab.fr' # known wrong address

   197  fixed_addr = 'cubicweb@logilab.fr'

   198  configured_addr = config.get('sender-addr')

   199  # check that the address has not been hand fixed by a sysadmin

   200  if configured_addr == wrong_addr: 

   201      config['sender-addr'] = fixed-addr

   202      config.save()

   203 

   204 Example 2: checking the value of the database backend driver, which

   205 can be useful in case you need to issue backend-dependent raw SQL

   206 queries in a migration script.

   207 

   208 .. sourcecode:: python

   209 

   210  dbdriver  = config.sources()['system']['db-driver']

   211  if dbdriver == "sqlserver2005":

   212      # this is now correctly handled by CW :-)

   213      sql('ALTER TABLE cw_Xxxx ALTER COLUMN cw_name varchar(64) NOT NULL;')

   214      commit()

   215  else: # postgresql

   216      sync_schema_props_perms(ertype=('Xxxx', 'name', 'String'),

   217      syncperms=False)

   218