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POGroovy Map vs. Table Relations within Domain Classes - How to decribe & persist this?
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  1. POGroovy Map vs. Table Relations within Domain Classes - How to decribe & persist this?
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    copied!<p>In Grails/Gorm I am storing a <strong>physical site</strong> which <strong>holds objects</strong> at <strong>defined positions</strong>.</p> <p>The domain class would simply be:</p> <h3>EXAMPLE A</h3> <p><em>SITE DC</em></p> <ul> <li>sitename</li> <li>positionmap (1: dog, 2: cat, 3:foo, 4:bar, ... up to an average of 30 items)</li> </ul> <p>... but the objects change their positions and I need to later be able to see WHICH positions were occupied by WHAT at a given time (WHEN).</p> <p>Thus I added another domain class</p> <h3>EXAMPLE B</h3> <p><em>POSITIONS DC</em></p> <ul> <li>validfrom</li> <li>validto</li> <li>positionmap (1: dog, 2: cat, 3:foo, 4:bar)</li> <li>belongsTo <em>SITE</em></li> </ul> <p><em>SITE DC</em></p> <ul> <li>sitename</li> </ul> <p>As all the objects will have a description AND there will be loads of SITEs using the same objects in it, I added a domain class to hold each and every OBJECT. Result:</p> <h3>EXAMPLE C</h3> <p><em>OBJECT DC</em></p> <ul> <li>name</li> <li>description</li> </ul> <p><em>POSITIONS DC</em></p> <ul> <li>validfrom</li> <li>validto</li> <li>positionmap (1: reference_to_dog, 2: reference_to_cat, 3:reference_to_foo, 4:reference_to_bar)</li> <li>belongsTo <em>SITE</em></li> </ul> <p><em>SITE DC</em></p> <ul> <li>sitename</li> </ul> <p><em>Now the Map, to me, doesn't seem reasonable anymore.</em></p> <p>I am thinking about removing the map, replacing it by yet another domain class:</p> <h3>EXAMPLE D</h3> <p><em>OBJECT DC</em></p> <ul> <li>name</li> <li>description</li> </ul> <p><em>OBJECT-TO-POSITION DC</em></p> <ul> <li>positionnumber (1, 2, 3, 4, ...)</li> <li>object (reference_to_cat, reference_to_dog, reference_to_foo, ...)</li> <li>belongsTo <em>POSITIONS</em></li> </ul> <p><em>POSITIONS DC</em></p> <ul> <li>validfrom</li> <li>validto</li> <li>belongsTo <em>SITE</em></li> </ul> <p><em>SITE DC</em></p> <ul> <li>sitename</li> </ul> <h3>QUESTIONS</h3> <ol> <li>Is it generally a good/bad idea to put maps into the database?</li> <li>How could this be achieved easier?</li> <li>What's the most performant way to do it?</li> </ol> <h3>EDIT: A NEW APPROCH BASED ON ROBS ANSWER</h3> <p>Inspired by your suggestion, Rob, I drafted this data model which grants a "front-row" role to the "SeasonPlan" (amended "ResidenceHistory").</p> <pre><code>class Zoo { static hasMany = [seasons: SeasonPlan] String name } // one way of representing histories class SeasonPlan = { static belongsTo = [zoo: Zoo] // a SeasonPlan belongs to a single particular Zoo static hasMany = [cages: Cage] DateTime from DateTime until } class Cage { static belongsTo = [seasonPlan: SeasonPlan] // a cage belongs to a single seasonplan Species species // a cage has a single Species Integer cageNumber } class Species { // static hasMany = [cages: Cage] // commented out - no reverse-lookup necessary String name } </code></pre> <p>This has one drawback: For every season plan there's a new cage - though <em>in reality the cages stay the same</em>! (Imagine a "Integer squareMeters" within the "Cage" to make it more obvious why this isn't desired.)</p> <p>For me applying such a thing to a data model is often hard to comprehend - <strong>how do I fit "pseudo-static" data like this into the application while retaining real-world corelation?</strong></p> <p>I hope what I mean is understandable - sorry if not.</p>
 

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