Odoo - How Does Odoo Server Load Addons and Modules?
Method load_addons in http.py
Odoo starts loading addons when it receives the first HTTP request. In the __call__ method of http.py file,
it calls load_addons to load all addons in the specified addon paths.
It uses a global variable addons_module and addons_manifest to track all modules from loaded addons.
For all addon paths passed in Odoo configuration parameters, it list sorted items including both files and folders in the path.
For each item, it checks whether the __openerp__.py manifest file and the static folder exist.
If both exist, it reads the manifest and remember its addon path. It imports all modules that have a static folder.
Finally it sets WSGI middleware for static folders.
Method load_modules in openerp/modules/loading.py
This method is called after the above load_addons method -- when a new registry is created first time for a database name.
It first checks if the database is initialized by checking if ir_module_module table exists.
It not initialized, it calls openerp.modules.db.initialize to initialize the database.
It then calls RegistryManager.get method for the database name.
It builds a graph from module's dependency declaration in 9 steps. Initially the graph is created with the base module.
Step 1: Load base module
For the graph that only has the base module, it calls the load_module_graph to
1)import the Python module by calling the load_openerp_module method in module.py
that calls __import__('openerp.addons.' + module_name) to import all modules with a openerp.addons. prefix.
2) create all model classes and instances defined in the module and keep them in registry;
For the base module, there are 96 models such as ir.model and ir.model.fields.
The load and setup_models of the registry.py are used to create model classes/instances and their fields.
Now all base models are available from the registry.
Step 2: Mark other modules to be loaded/updated
For modules specified in 'init' and 'update' parameters, install and upgrade these module and set their state to 'installed'.
Step 3: Load marked modules
It first calls load_marked_modules to load modules whose states is in the list of ['installed', 'to upgrade', 'to remove'].
Add them to graph based their dependencies. The create and set model classes/instances and fields for models defined in these modules.
For update modules, do the same thing for those modules whose state is 'to install'.
Step 4-9: Finish, clean up and more
Step 4: Finish and clean up installations.
Step 5: Remove unused menu items.
Step 6: Check and remove modules and reset environment and registry manager.
Step 7: Verify custom views on every model
Step 8: Call model registry hook -- not used by any model
Step 9: Run post-install module unit tests.
Please try to give a substantial answer. If you wanted to comment on the question or answer, just use the commenting tool. Please remember that you can always revise your answers - no need to answer the same question twice. Also, please don't forget to vote - it really helps to select the best questions and answers!