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devel:django_introduction [2008/08/25 10:44]
jodal Document the improved inner workings of nav.django.urls.
devel:django_introduction [2009/06/17 08:46]
jorabra Add missing word
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 ===== nav.django package ===== ===== nav.django package =====
  
-As NAV has not used Django from the very beginning, NAV does not strictly follow the Django convention of multiple apps with their own models, views, etc. To plug NAV into the Django framework some glue is needed. This glue and other common Django-related code is located in the ''​nav.django''​ Python package, which is located in ''​subsystem/​lib-python/src/​nav/​django''​.+As NAV has not used Django from the very beginning, NAV does not strictly follow the Django convention of multiple apps with their own models, views, etc. To plug NAV into the Django framework some glue is needed. This glue and other common Django-related code is located in the ''​nav.django''​ Python package, which is located in ''​subsystem/​lib-python/​nav/​django''​.
  
 ==== Settings ==== ==== Settings ====
  
-The usual Django settings file is located at ''​nav.django.settings''​. The end-users do not need to modify this settings file when deploying NAV, as all options are derived from existing NAV configuration in i.e. the files ''​nav.conf''​ and ''​db.conf''​.+The usual Django settings file is located at ''​nav.django.settings''​. The end-users do not need to modify this settings file when deploying NAV, as all options are derived from existing NAV configuration in the files ''​nav.conf''​ and ''​db.conf''​.
  
 Note that there is no ''​INSTALLED_APPS''​ setting. NAV does not use this setting at all, due to a different file organization than what Django expects. Following from this, Django does not have a concept of what is an app in NAV. An app is just defined in the minds of the developers. This also means that NAV to a very little degree may take advantage of the ''​django-admin.py''​ executable, including features like ''​syncdb''​ for creating database tables for new apps. Note that there is no ''​INSTALLED_APPS''​ setting. NAV does not use this setting at all, due to a different file organization than what Django expects. Following from this, Django does not have a concept of what is an app in NAV. An app is just defined in the minds of the developers. This also means that NAV to a very little degree may take advantage of the ''​django-admin.py''​ executable, including features like ''​syncdb''​ for creating database tables for new apps.
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 ==== URL configuration ==== ==== URL configuration ====
  
-In ''​nav.django.urls''​ the root URL configuration for all things ​Django in NAV is located''​nav.django.urls''​ is not only a module, but also a package. The ''​%%__init__.py%%''​ file in the package imports all submodules it can find in the file system, calls ''​get_urlpatterns()''​ on all the submodules, and combines the results into one ''​urlpatterns''​ list, as all Django URL configurations does.+The root URL configuration for all Django-related applications ​in NAV is located ​in ''​nav.django.urls''​. It is not only a module, but also a package. The ''​%%__init__.py%%''​ file in the package imports all submodules it can find in the directory, calls ''​get_urlpatterns()''​ on all the submodules, and combines the results into one ''​urlpatterns''​ list, as all Django URL configurations does.
  
-In other words, when creating a new Django app in a branch of its ownyou simply drop a new submodule for your app into the ''​subsystem/​lib-python/​src/​nav/​django/​urls/''​ folder, run ''​make install''​ in ''​subsystem/​lib-python/​''​ and then the NAV installation will find your app. If somebody else runs ''​make install''​ in their version of ''​subsystem/​lib-python/​''​ they will not overwrite ​the URL configuration for your new app, unless they use exactly the same name for the submodule as you did.+When creating a new Django app, create ​a new submodule for your app in the ''​subsystem/​your_app/​nav/​django/​urls/''​ folder, run ''​make install''​ in your app to install the module into the ''​nav.django.urls'' ​package, ​and the NAV installation will find your app. If somebody else installs URLconf glue into ''​nav.django.urls''​ they will not affect ​the URL configuration for your app, unless they use exactly the same name for the submodule as you did. For details, check out the ''​ipdevinfo''​ subsystem and its ''​Makefile.in''​.
  
 === nav.django.urls.urlbuilder === === nav.django.urls.urlbuilder ===
  
-There is one special submodule named ''​nav.django.urls.urlbuilder''​. This is simply a Django replacement for the archaic ''​nav.web.urlbuilder''​. It is used by Django apps to link to non-Django apps, like the report subsystem, through the use of the ''​url''​ template tag or the ''​reverse()''​ function, instead of using the archaic ''​nav.web.urlbuilder''​. From your code's point of view, the URL configurations in ''​nav.django.urls.urlbuilder''​ is used as any other URL configuration in NAV.+There is one special submodule named ''​nav.django.urls.urlbuilder''​. This is simply a Django replacement for the archaic ''​nav.web.urlbuilder''​. It is used by Django apps to link to non-Django apps, like the report subsystem, through the use of the ''​url''​ template tag or the ''​reverse()''​ function, instead of using the archaic ''​nav.web.urlbuilder''​. From your code's point of view, the URL configurations in ''​nav.django.urls.urlbuilder''​ is used as any other Django ​URL configuration in NAV.
  
 ==== Shortcuts ==== ==== Shortcuts ====
  
-Since before Django, NAV has been using the Cheetah template system. To enable the use of Django templates for Django apps, while still integrating with the existing template hierarchy of NAV, some shortcut functions ​has been created in ''​nav.django.shortcuts''​. At the time of writing, the shortcuts are ''​render_to_response()'',​ ''​object_list()'',​ and ''​object_detail()''​. ''​render_to_response()''​ is analogous to the well known ''​django.shortcuts.render_to_response()'',​ and ''​object_list()''​ and ''​object_detail()''​ are analogous to functions in ''​django.views.generic.list_detail''​.+Since before Django, NAV has been using the Cheetah template system. To enable the use of Django templates for Django apps, while still integrating with the existing template hierarchy of NAV, some shortcut functions ​have been created in ''​nav.django.shortcuts''​. At the time of writing, the shortcuts are ''​render_to_response()'',​ ''​object_list()'',​ and ''​object_detail()''​. ''​render_to_response()''​ is analogous to the well known ''​django.shortcuts.render_to_response()'',​ and ''​object_list()''​ and ''​object_detail()''​ are analogous to functions in ''​django.views.generic.list_detail''​.
  
 The difference between the original functions from Django and the ones provided in ''​nav.django.shortcuts''​ is that the NAV versions take an additional first argument, namely ''​cheetah_template_func''​. ''​cheetah_template_func''​ is assumed to be a Cheetah template function, which returns a Cheetah template with a ''​content_string''​ variable. The shortcuts takes the content which Django normally would have returned, and inserts it into the ''​content_string''​ variable of the Cheetah template. In other words, a Django template is rendered as usual, and then the result are wrapped into a Cheetah template. The difference between the original functions from Django and the ones provided in ''​nav.django.shortcuts''​ is that the NAV versions take an additional first argument, namely ''​cheetah_template_func''​. ''​cheetah_template_func''​ is assumed to be a Cheetah template function, which returns a Cheetah template with a ''​content_string''​ variable. The shortcuts takes the content which Django normally would have returned, and inserts it into the ''​content_string''​ variable of the Cheetah template. In other words, a Django template is rendered as usual, and then the result are wrapped into a Cheetah template.
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 ==== Context processors ==== ==== Context processors ====
  
-At the time of writing, ''​nav.django.context_processors''​ only contains one context ​processors: ''​debug''​. If Django is run in debug mode, this context ​processors ​appends a ''​sql_queries''​ variable to the context of all templates, containing all SQL queries executed to generate the current page. This is useful for optimizing the use of the Django ORM.+At the time of writing, ''​nav.django.context_processors''​ only contains one context ​processor: ''​debug''​. If Django is run in debug mode, this context ​processor ​appends a ''​sql_queries''​ variable to the context of all templates, containing all SQL queries executed to generate the current page. This is useful for optimizing the use of the Django ORM.
  
  
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 In addition ''​nav/​web/​templates/''​ contains a Cheetah template (not runnable Python code, but it will be compiled to a runnable Python file during installation) which is used to wrap around the Django templates. The Django templates themselves are not runnable Python code, but HTML files with some additional syntax, and are thus available directly in the ''​templates/''​ folder, not within the ''​nav/''​ folder. The Django templates are installed to a ''​templates/''​ folder next to the ''​python/''​ folder where all installed Python code goes. Typically this is ''/​usr/​local/​nav/​lib/​templates/''​. In addition ''​nav/​web/​templates/''​ contains a Cheetah template (not runnable Python code, but it will be compiled to a runnable Python file during installation) which is used to wrap around the Django templates. The Django templates themselves are not runnable Python code, but HTML files with some additional syntax, and are thus available directly in the ''​templates/''​ folder, not within the ''​nav/''​ folder. The Django templates are installed to a ''​templates/''​ folder next to the ''​python/''​ folder where all installed Python code goes. Typically this is ''/​usr/​local/​nav/​lib/​templates/''​.
  
-Further, the file ''​ipdevinfo.tool''​ defines the name, description,​ icon and URL of the IP Device Info tool in NAV's toolbox. The file ''​htaccess''​ is the only file which is installed into the ''​ipdevinfo/''​ folder in the web server'​s document root. It simply states that all URLs starting with i.e. ''​http://​nav.example.com/​ipdevinfo/''​ are to be handled by a Python program, namely Django'​s mod_python handler, using ''​nav.django.settings''​ as configuration. In other words, the htaccess file should be identical for all Django apps in NAV.+Further, the file ''​ipdevinfo.tool''​ defines the name, description,​ icon and URL of the IP Device Info tool in NAV's toolbox. The file ''​htaccess''​ is the only file which is installed into the ''​ipdevinfo/''​ folder in the web server'​s document root. It simply states that all URLs starting with ''​http://​nav.example.com/​ipdevinfo/''​ are to be handled by a Python program, namely Django'​s mod_python handler, using ''​nav.django.settings''​ as configuration. In other words, the htaccess file should be identical for all Django apps in NAV
 + 
 +Finally, the folder ''​media/''​ contains all static media which is needed by the app. Typically, this should be ''​media/​style/''​ for CSS-files, ''​media/​js/''​ for JavaScript, and ''​media/​images/''​ for images. Files should typically be named after the app to avoid name collisions with other apps when installed, i.e. ''​media/​style/​ipdevinfo.css''​ and subfolders like ''​media/​images/​ipdevinfo/''​. 
 + 
 +Configuration files should be in the ''​config/''​ folder in the source tree, and installed into ''​$NAVHOME/​etc/​appname/''​.
  
 How to install everything mentioned here is defined in ''​Makefile.in''​. How to install everything mentioned here is defined in ''​Makefile.in''​.
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   - The matching part of the URL, that is ''/​ipdevinfo/''​ is stripped and the rest is passed to ''​nav.web.ipdevinfo.urls''​ for further lookup.   - The matching part of the URL, that is ''/​ipdevinfo/''​ is stripped and the rest is passed to ''​nav.web.ipdevinfo.urls''​ for further lookup.
   - As the URL now is empty, it matches the ''​^$''​ pattern in ''​nav.web.ipdevinfo.urls''​ and the ''​search''​ view, as imported from ''​nav.web.ipdevinfo.views''​ is called.   - As the URL now is empty, it matches the ''​^$''​ pattern in ''​nav.web.ipdevinfo.urls''​ and the ''​search''​ view, as imported from ''​nav.web.ipdevinfo.views''​ is called.
-  - The ''​search''​ view does its job, i.e. either creating a search form, and if a query already has been issued, looking up IP devices matching the query.+  - The ''​search''​ view does its job, i.e. either creating a search form, or if a query already has been issued, looking up IP devices matching the query.
   - Finally, the view calls ''​nav.django.shortcuts.render_to_response()''​ with the following arguments: a Cheetah template, a Django template, the form, the query string, the search results and a list of error mesages if any.   - Finally, the view calls ''​nav.django.shortcuts.render_to_response()''​ with the following arguments: a Cheetah template, a Django template, the form, the query string, the search results and a list of error mesages if any.
   - ''​render_to_response()''​ uses Django'​s own ''​render_to_response()''​ implementation to render the Django template. Then the result is inserted into the ''​content_string''​ variable of the given Cheetah template. Finally, the result of the Cheetah template is extracted and inserted into a Django ''​HttpResponse'',​ which is returned to the ''​search()''​ view.   - ''​render_to_response()''​ uses Django'​s own ''​render_to_response()''​ implementation to render the Django template. Then the result is inserted into the ''​content_string''​ variable of the given Cheetah template. Finally, the result of the Cheetah template is extracted and inserted into a Django ''​HttpResponse'',​ which is returned to the ''​search()''​ view.
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 ==== mod_python and Django sessions ==== ==== mod_python and Django sessions ====
  
-NAV uses sessions for keeping track of logged in users. Currently, we are not using ''​django.contrib.sessions'',​ but are still using plain old ''​mod_python'' ​sessions. For now, the easiest way to get hold of the ''​mod_python'' ​session in views is to use ''​request._req.session'',​ where ''​request._req''​ is the traditional ''​mod_python''​ request object. In the future, one should look into using Django'​s authentication and session frameworks.+NAV uses sessions for keeping track of logged in users. Currently, we are not using ''​django.contrib.sessions'',​ but are still using a session library developed specifically for NAV.  This session library attaches session objects to ''​mod_python''​'s request objects For now, the easiest way to get hold of the NAV session in views is to use ''​request._req.session'',​ where ''​request._req''​ is the traditional ''​mod_python''​ request object. In the future, one should look into using Django'​s authentication and session frameworks.
  
 ==== Base template using Django templates ==== ==== Base template using Django templates ====
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 ==== Unit testing ==== ==== Unit testing ====
  
-NAV should certainly start using unit testing. Tests for i.e. ''​nav.web.ipdevinfo''​ could for example go into ''​nav.web.ipdevinfo.tests'',​ but this should be synchronized with Django conventions,​ and one must also find a way to run the tests, most probably through a custom test runner or something. The point is, one needs to give this some thought, and the sooner the better. New Django apps in NAV should really have unit tests from the start.+NAV should certainly start using unit testing. Tests for ''​nav.web.ipdevinfo''​ could for example go into ''​nav.web.ipdevinfo.tests'',​ but this should be synchronized with Django conventions,​ and one must also find a way to run the tests, most probably through a custom test runner or something. The point is, one needs to give this some thought, and the sooner the better. New Django apps in NAV should really have unit tests from the start. 
devel/django_introduction.txt · Last modified: 2010/01/13 11:30 by eide