StackOverflow2013

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POQt thick database client architecture
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copied!<p>My goal is to create a thick client to the database. Basically it is all about managing three lists of data.</p> <p>I would like to slice my application into decoupled layers so using Qt's Model/View framework seems natural to me.</p> <ul> <li>When should I create QSql*Model instances?</li> </ul> <p>I need to be able to connect/disconnect to/from the database several times (I have menu items for that). I'm not happy with deleting a bunch of models and creating them once again upon every connect/disconnect.</p> <p>Is there any alternative approach?</p> <ul> <li>Where should I create QSql*Model instances?</li> </ul> <p>I don't think MainWindow or any other GUI-related class is supposed to hold the code like this:</p> <pre><code>m_goodsModel->setRelation(1, QSqlRelation("Level", "LevelId", "Name")); </code></pre> <p>I want to decouple the GUI from the data structure. Any ideas how to do that?</p> <ul> <li>When and where should I bind my views to models?</li> </ul> <p>I need to represent my three lists in a dozen of ways. If I recreate the models every time I connect/disconnect I will need to inject newly created models into all the views again.</p> <p>It would be great if I could do that only once, but I have no clue how.</p> <ul> <li>What to do with the nasty <code>QSqlTableModel::select()</code> method?</li> </ul> <p>This one drives me crazy. In contrast to other models (e.g. <code>QStringListModel</code>, <code>QFileSystemModel</code>, etc) where the data is ready to use out of the box, models derived from <code>QSqlTableModel</code> are useless until you manually invoke their <code>select()</code> method. Before that invocation the model is empty so as the views using that model; the header data is not populated either, so the view doesn't even know what columns does it have to render.</p> <p>As I cannot avoid <code>select()</code> invocation I wonder where should I put it so that it fits nice? I don't think MainWindow or any other GUI-related classes should contain that code.</p> <ul> <li>Performance and robustness</li> </ul> <p>I'm not happy to reinitialize everything upon db reconnection. It takes too long to do that (I mean during execution). I also would like to avoid crashes during model recreation process as the views may still refer to them.</p> <p>Isn't there any other way to set everything just once and handle reconnection gracefully?</p>

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