lodel2_mirror/plugins/mongodb_datasource/__init__.py

#-*- coding: utf-8 -*-
__plugin_type__ = 'datasource'
__plugin_name__ = 'mongodb_datasource'
__version__ = '0.0.1'
__plugin_type__ = 'datasource'

__loader__ = "main.py"
__confspec__ = "confspec.py"

__author__ = "Lodel2 dev team"
__fullname__ = "MongoDB plugin"


## @brief Activates the plugin
#
# @note It is possible there to add some specific actions (like checks, etc ...) for the plugin
#
# @return bool|str : True if all the checks are OK, an error message if not
def _activate():
    from lodel import buildconf
    return buildconf.PYMONGO

#
#   Doxygen comments
#

##@defgroup plugin_mongodb_datasource MongoDB datasource plugin
#@brief Doc about mongodb datasource

##@page plugin_mongodb_backref_complexity Reflexion on back reference complexity
#@ingroup plugin_mongodb_bref_op
#
#Their is a huge performance issue in the way we implemented references
#and back references for mongodb datasource :
#
#For each write action (update, delete or insert) we HAVE TO run a select
#on all concerned LeObject. In fact those methods headers looks like
#<pre>def write_action(target_cls, filters, [datas])</pre>
#
#We have no idea if all the modified objects are of the target class (they
#can be of any target's child classes). So that means we have no idea of the
#@ref base_classes.Reference "References" that will be modified by the action.
#
#Another problem is that when we run an update or a delete we have no idea
#of the values that will be updated or deleted (we do not have the concerned
#instances datas). As a result we cannot replace or delete the concerned
#back references.
#
#In term of complexity the number of DB query looks like :
#<pre>
#With n the number of instances to modify : 
#queryO(n) ~=  2n ( n * select + n * update )
#</pre>
#But it can go really bad, really fast if we take in consideration that
#query's can be done on mixed classes or abstract classes. With :
#- n : the number of LeObect child classes represented by the abstract class
#- m : the number of LeObject child classes for each n
#- o : the number of concerned back_reference classes for each m
#
#<pre>queryO(n,m,o) ~=  n + (n*m) + (n*m*o) => n + n*m select and n*m*o updates</pre>
#
#All of this is really sad especially as the update and the delete will be
#run on LeObject instances....
#