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POWhy @OneToMany does not work with inheritance in Hibernate
 

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  1. POWhy @OneToMany does not work with inheritance in Hibernate
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    <pre><code>@Entity @Inheritance(strategy = InheritanceType.SINGLE_TABLE) public class Problem { @ManyToOne private Person person; } @Entity @DiscriminatorValue("UP") public class UglyProblem extends Problem {} @Entity public class Person { @OneToMany(mappedBy="person") private List&lt; UglyProblem &gt; problems; } </code></pre> <p>I think it is pretty clear what I am trying to do. I expect @ManyToOne person to be inherited by UglyProblem class. But there will be an exception saying something like: "There is no such property found in UglyProblem class (mappedBy="person")".</p> <p>All I found is <a href="http://opensource.atlassian.com/projects/hibernate/browse/ANN-558" rel="nofollow noreferrer">this</a>. I was not able to find the post by Emmanuel Bernard explaining reasons behind this. </p> <hr> <blockquote> <p>Unfortunately, according to the Hibernate documentation "Properties from superclasses not mapped as @MappedSuperclass are ignored."</p> </blockquote> <p>Well I think this means that if I have these two classes:</p> <pre><code>public class A { private int foo; } @Entity public class B extens A { } </code></pre> <p>then field <code>foo</code> will not be mapped for class B. Which makes sense. But if I have something like this:</p> <pre><code>@Entity public class Problem { @Id @GeneratedValue(strategy = GenerationType.AUTO) private Long id; private String name; public Long getId() { return id; } public void setId(Long id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } } @Entity public class UglyProblem extends Problem { private int levelOfUgliness; public int getLevelOfUgliness() { return levelOfUgliness; } public void setLevelOfUgliness(int levelOfUgliness) { this.levelOfUgliness = levelOfUgliness; } } </code></pre> <p>I expect the class UglyProblem to have fileds <code>id</code> and <code>name</code> and both classes to be mapped using same table. (In fact, this is exactly what happens, I have just checked again). I have got this table:</p> <pre><code>CREATE TABLE "problem" ( "DTYPE" varchar(31) NOT NULL, "id" bigint(20) NOT NULL auto_increment, "name" varchar(255) default NULL, "levelOfUgliness" int(11) default NULL, PRIMARY KEY ("id") ) AUTO_INCREMENT=2; </code></pre> <p>Going back to my question:</p> <blockquote> <p>I expect @ManyToOne person to be inherited by UglyProblem class.</p> </blockquote> <p>I expect that because all other mapped fields are inherited and I do not see any reason to make this exception for ManyToOne relationships.</p> <hr> <p>Yeah, I saw that. In fact, I used Read-Only solution for my case. But my question was "Why..." :). I know that there is an explanation given by a member of hibernate team. I was not able to find it and that is why I asked.</p> <p>I want to find out the motivation of this design decision.</p> <p>(if you interested how I have faced this problem: I inherited a project built using hibernate 3. It was Jboss 4.0.something + hibernate was already there (you'd download it all together). I was moving this project to Jboss 4.2.2 and I found out that there are inherited mappings of "@OneToMany mappedBy" and it worked fine on old setup...)</p>
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    1. COYou should add more details about your edit on September 4. Specifying List<UglyProblem> instead of only List in the @OneToMany(mappedBy="person") mapping changes the nature of the problem, since I think we previously assumed you wanted to map a Person to a list of Problems (not Ugl
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      1. USDavid Crow
 

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