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POHow to define column that is not actually related to another table by keys, but by keywords
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  1. POHow to define column that is not actually related to another table by keys, but by keywords
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    copied!<p>I am using JPA to see how helpful it will be, rather than using straight SQL, and I realized today that one of my columns is incorrect.</p> <p>I have a playlist application. Each playlist has a title and a list of keywords that signify the songs to include.</p> <p>So, I may have this as one row, where there are three keywords. Exercise steady-beat_country hard_rock classic_rock</p> <p>If I add a new song that has one of these keywords applied to it, I want it to be pulled up when I select this playlist.</p> <p>I could just go through all the playlists that have this keyword and relate the new song with the playlist, but that seems to be very inefficient, if I have several users each with many playlists, if the song can be played by all the users.</p> <p>I am curious if I should just do this in my <code>@Entity</code> model, which is written in <code>Scala</code>:</p> <pre><code>@transient var songs : java.util.List[Song] = new java.util.ArrayList[Song]() @OneToMany{val cascade=Array(CascadeType.ALL), val mappedBy="playlist"} var keywords : java.util.List[Snippet] = new java.util.ArrayList[Snippet]() </code></pre> <p>Then I could just load the keywords that are actually related to the playlist and then call a named query that can load up the songs by a list of keywords.</p> <p>Or, is there a way to define something like this in JPA so I don't have to make an extra call?</p> <p><strong>UPDATE:</strong></p> <p>Tonight I test this, but I am wondering if I could set up my named query to do this query, so it would be something like:</p> <p><code>SELECT Playlist p, Songs s WHERE p.user = :user AND s.keywords IN (p.keywords)</code></p> <p>This code is a bit flawed as the IN I need to look up how I can do it in JPA, I may need to store the keywords as comma-delimited, but I am not certain yet how I can have the songs fill in the <code>song</code> property for <code>playlist</code>.</p>
 

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