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POIf not polymorphism, how do I model these classes
 

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  1. POIf not polymorphism, how do I model these classes
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    <p>Ok so say I'm modelling the following Football Club: All people are Individuals. A Player is a person and therefore extends an Individual. A Member is a person and therefore extends an Individual.</p> <p>Superclass: </p> <pre><code>Individual {name, eyeColour} </code></pre> <p>Subclasses: </p> <pre><code>Player extends Individual {position} Member extends Individual {subscription} </code></pre> <p>Tom is the owner of the Football Club: </p> <pre><code>Individual i = new Individual("Tom", "Blue") </code></pre> <p>Bob &amp; Tony are Players:</p> <pre><code>Player p1 = new Player("Bob", "Green", "Goalkeeper") Player p2 = new Player("Tony", "Blue", "Striker") </code></pre> <p>Steve is a Member:</p> <pre><code>Member m = new Member("Steve", "Brown", 5.00) </code></pre> <p>Individuals, Players and Members are all persisted to the same Kind (Individual) in the GAE datastore using Objectify.</p> <pre> name eyeColour position subscription ^d Tom Blue [missing] [missing] Individual Bob Green Goalkeeper [missing] Player Tony Blue Striker [missing] Player Steve Brown [missing] 5.00 Member </pre> <p>What if e.g. Bob decides to become a Member as well as a Player? I want to store is subscription. I can't upcast Bob to an Individual and then downcast to a Member. Java doesn't allow this. I can't create a new Member and copy all the properties of Bob's Player object and store it back with the same id - I'll lose his Position property. I need Bob to be both a Member and a Player in the datstore but NOT in object form (I'm not after multi-inheritance) I still want to get(Player.class,"Bob") and have a Player object or get(Member.class,"Bob") and have a Member object. I won't need an Object that has both the position and subscription properties at the same time.</p> <p>I also want to avoid this is the datastore:</p> <pre> name eyeColour position subscription ^d Tom Blue [missing] [missing] Individual Bob Green Goalkeeper [missing] Player Bob Green [missing] 10.00 Member Tony Blue Striker [missing] Player Steve Brown [missing] 5.00 Member </pre> <p>because Bob now has data duplication on name and eyeColour which could lead to data inconsistancy.</p> <p>Any ideas for how to model this?</p> <p>Also what if Tom becomes a player, or Steve becomes a member?</p>
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    1. COAside from OO solution, can you really be a Player without being a Member?
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    2. COok so it's a bad example - assume players are not members by default.
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