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POCan I use dynamic relationships (or VIEWS) in SQLAlchemy ORM?
 

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  1. POCan I use dynamic relationships (or VIEWS) in SQLAlchemy ORM?
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    <p>I'm looking for a way, so that a relationship <em>only uses some rows of a table</em>, instead of the whole table. </p> <blockquote> <p>I was thinking about using a <strong>view</strong> instead of the original table as base for the relationship. Where the <em>view</em> contains only a filtered set of rows from the original table.</p> </blockquote> <h2>Example</h2> <p>I want to collect statistical information for songs (rating, play-count, last time played) from a couple of players over different devices and from different users. I use <em>Python</em> and <a href="http://www.sqlalchemy.org/" rel="nofollow noreferrer">SQL Alchemy</a>. </p> <p>I came up with the following table layout (you can take a look at the <a href="https://gist.github.com/brutus/7483771" rel="nofollow noreferrer">code for the objects</a> and the <a href="https://gist.github.com/brutus/7335121" rel="nofollow noreferrer">SQL for the tables</a>):</p> <p><img src="https://i.stack.imgur.com/Bbfh4.png" alt="ERP"></p> <h2>The problem</h2> <p>For each <code>Song</code> object I can easily get <em>all the associated</em> <code>Stats</code> objects. But most of the time I only want <em>some of them</em>. I only want those <code>Stats</code> for a <code>Song</code> that relate to one or more <code>Commit</code>, eg. only the data from all commits by a given user, or one certain commit. </p> <p><strong>So I need some way to filter the stats data on the song object.</strong></p> <p>I'm not quiet sure how to archive this. </p> <p>Should I use some custom query? But where do I place it and how? Also: while this might give me the data I want (<code>select path, rating... over the three joined tables</code> or <a href="https://gist.github.com/brutus/7486362" rel="nofollow noreferrer">something along those lines</a>), I won't get objects back.</p> <p>I was thinking about using a <strong>view</strong> on the <code>stats</code> table, containing only the lines matching the given <code>commits</code>. The view has to be created dynamically trough, so different commits can be filtered. And than using this view as the base for a relationship from <code>songs</code> to <code>stats</code>. But I have no idea how to do it.</p> <p>So: Any ideas on how to solve this problem? </p> <p>Or how to solve this another way?</p>
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    1. CORight now I use direct SQL queries like [this](https://gist.github.com/brutus/7486362). It gives me the data, but I much rather like to have the `Song` objects and only the filtered `Stats` mapped to it, so I can process them further on the `Song` object.
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    2. COI have an idea on how this could be accomplished, but I need a few more details. Would this view be temporary or materialized? Are you using Postgresql? So what you'd like is in python to create a view on the first time Stats is queried with a commit_id. All subsequent queries for that query will use that view, instead of the original table?
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