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POHibernate/JPA Mapping on abstract class
 

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  1. POHibernate/JPA Mapping on abstract class
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    <p>What would be the best practice to implement the following situation with Hibernate.</p> <p>We define an abstract class that will form the base of any object that we want to persist in our database. It contains the id etc etc...</p> <pre><code>public abstract class ModelObject { protected int id; ... } </code></pre> <p>Now we subclass our base clase for special cases where more than one entity will have a similar fields.</p> <pre><code>public abstract class ModelObjectWithNose extends ModelObject { ... protected Nose nose; } </code></pre> <p>Now, for all classes that we want to have a <code>Nose</code>:</p> <pre><code>public class Person extends ModelObjectWithNose { ... } public class Animal extends ModelObjectWithNose { ... } </code></pre> <p>The real problem we have at the moment now is that this relationship needs to be bi-directional. Each concrete class needs to know which <code>Nose</code> is theirs, but each <code>Nose</code> also needs to know to what object it belongs.</p> <pre><code>public class Nose { ... private ModelObjectWithNose owner; } </code></pre> <p>For our example we need a <code>@OneToOne</code> relationship, as each <code>Person</code> can only have one <code>Nose</code> and each <code>Nose</code> can only belong to one <code>Person</code>.</p> <p>What we have tried is doing the following:</p> <pre><code>@Entity @Inheritance(strategy = InheritanceType.JOINED) public abstract class ModelObjectWithNose extend ModelObject { ... } </code></pre> <p>and then:</p> <pre><code>@Entity public class Person extends ModelObjectWithNose { ... } </code></pre> <p>...etc etc etc.</p> <p>1) How do I define the relationship between the <code>Nose</code> and the <code>ModelObjectWithNose</code>? Is it as simple as:</p> <pre><code>@Entity public class Nose { ... // this causes: 'Basic' attribute should not be 'Persistence Entity' ModelObjectWithNose owner; } </code></pre> <p>2) Is there a better / more preferred way? Would the inheritance strategy work properly?</p> <p>Thanks! </p> <p><em><strong>EDIT</em></strong></p> <p>So I have tried a few ways which all seem to potentially work. Using any of the three Inheritance schemes works fine if you set up the annotations as in the question. Unfortunately this has a huge impact on our existing database and code, so we opted to (for now) simply index the <code>Nose</code> object's <code>id</code> field that is kept on our current objects that would have extended <code>ModelObjectWithNose</code> and simply write helper methods to do point queries to find the entries.</p>
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    1. USNico Huysamen
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    1. COWhere are `@OneToOne`s in your mapping?
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    2. CO@axtavt - So the @OneToOne would be on both `ModelObjectWithNose` in the `Nose` class, and on `Nose` in the `ModelObjectWithNose`. Please see my edit for further details.
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    3. COWould you like to elaborate on the "huge impact" the various inheritance strategies have on your code? It'd be interesting to read.
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      1. USTom Anderson
 

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