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<p class="MsoNormal"><span lang="EN-US" style="font-size:10.5pt;font-family:"Calibri","sans-serif";color:#1F497D">Hi, Vega,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:10.5pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:10.5pt;font-family:"Calibri","sans-serif";color:#1F497D">Multiple DB access will be a use case for one session , especially for DB data insertion, multiple table will be involved. To embed the session
in Context, it’s ok to start a session if the session is empty, but how to decide when to commit the data, end a session?
<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:10.5pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal" style="text-align:justify;text-justify:inter-ideograph"><span lang="EN-US" style="font-size:10.5pt;font-family:"Calibri","sans-serif";color:#1F497D">Best Regards<o:p></o:p></span></p>
<p class="MsoNormal" style="text-align:justify;text-justify:inter-ideograph"><span lang="EN-US" style="font-size:10.5pt;font-family:"Calibri","sans-serif";color:#1F497D">Chaoyi Huang ( Joe Huang )</span><span lang="EN-US" style="font-size:10.5pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:10.5pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span lang="EN-US" style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">From:</span></b><span lang="EN-US" style="font-size:10.0pt;font-family:"Tahoma","sans-serif""> Vega Cai [mailto:luckyvega.g@gmail.com]
<br>
<b>Sent:</b> Thursday, July 30, 2015 3:03 PM<br>
<b>To:</b> openstack-dev@lists.openstack.org<br>
<b>Subject:</b> [openstack-dev] [tricircle] DAL implementation<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US">Hi folks,<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US">In my current implementation, there are a core module and a models module. Core module handles all the database stuff, start a session, issue sql operation, then end a session. Models module invokes methods in core module
to access database, as showed below:<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US">model.py<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US">def get_site(site_id):<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US"> core.get_resource(Site, site_id)<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US">core.py<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US">def get_resource(model, pk_value):<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US"> # code to access database<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US">To add context, I am going to implement like this:<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US">model.py<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US">def get_site(context, site_id):<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US"> policy_check(context)<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US"> core.get_resource(Site, site_id)<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US">core.py<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US">def get_resource(model, pk_value):<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US"> # code to access database<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US">So there is no need to embed session into context.<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US">One advantage of embedding session into context is that you can combine more than one method calls in one session, like:<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US">model.py<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US">def complex_operation(context):<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US"> policy_check(context)<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US"> with context.session.begin():<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US"> core.operation1(context)<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US"> core.operation2(context)<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US">But this approach moves session handling from core module to models module and core module just provides some utility methods.<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US">I'm not sure which one is better.<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US">BR<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US">Zhiyuan<o:p></o:p></span></p>
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