Can self-join and single-table inheritance co-exist in Ebean?

Joseph Conley

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Jan 23, 2012, 1:30:50 PM1/23/12

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I have a use case where I would like to implement both a self-join and single-table inheritance for the same entity. I have a NODE table with three fields, ID, Name, and parent_node_id (which is null if the node row is a root node). Here is my example with just the self-join, which works without issue.

public class Node {

@Id

public int id;

public String name;

@ManyToOne

@JoinColumn(name="parent_node_id")

public Node parent;

//TODO need to ensure children and fields are pre-fetched (can't fetch from within bean)

@OneToMany(mappedBy="parent")

public List<Node> children = new ArrayList<DataNode>();

}

Now, I'd like to add a discriminator column and subclass this Node class to achieve single-table inheritance, making my Node class abstract. However, when I try it with this setup (using NodeA as an implementing class of Node), I run into the following error:

Exception in thread "main" java.lang.RuntimeException: getIntercept children on [node.Node] type[node.NodeA$$EntityBean$exchange] threw error.

at com.avaje.ebeaninternal.server.deploy.BeanProperty.getValueIntercept(BeanProperty.java:912)

at com.avaje.ebeaninternal.server.deploy.BeanPropertyAssocMany.getValueIntercept(BeanPropertyAssocMany.java:189)

at com.avaje.ebeaninternal.server.deploy.BeanProperty.elGetValue(BeanProperty.java:937)

at com.avaje.ebeaninternal.server.query.CQuery.createNewDetailCollection(CQuery.java:632)

at com.avaje.ebeaninternal.server.query.CQuery.readBeanInternal(CQuery.java:596)

at com.avaje.ebeaninternal.server.query.CQuery.hasNextBean(CQuery.java:710)

at com.avaje.ebeaninternal.server.query.CQuery.readTheRows(CQuery.java:696)

at com.avaje.ebeaninternal.server.query.CQuery.readCollection(CQuery.java:663)

at com.avaje.ebeaninternal.server.query.CQueryEngine.findMany(CQueryEngine.java:203)

at com.avaje.ebeaninternal.server.query.DefaultOrmQueryEngine.findMany(DefaultOrmQueryEngine.java:96)

at com.avaje.ebeaninternal.server.core.OrmQueryRequest.findList(OrmQueryRequest.java:315)

at com.avaje.ebeaninternal.server.core.DefaultServer.findList(DefaultServer.java:1534)

at com.avaje.ebeaninternal.server.core.DefaultBeanLoader.loadMany(DefaultBeanLoader.java:162)

at com.avaje.ebeaninternal.server.core.DefaultServer.loadMany(DefaultServer.java:516)

at com.avaje.ebeaninternal.server.loadcontext.DLoadManyContext.loadMany(DLoadManyContext.java:158)

at com.avaje.ebean.common.AbstractBeanCollection.lazyLoadCollection(AbstractBeanCollection.java:147)

at com.avaje.ebean.common.BeanList.init(BeanList.java:116)

at com.avaje.ebean.common.BeanList.size(BeanList.java:408)

at com.mainstream.exchange.data.Test.main(Test.java:20)

Caused by: java.lang.RuntimeException: Not expecting this method to be called on [node.Node.children] as it is a NON ID property on an abstract class

at com.avaje.ebeaninternal.server.deploy.ReflectGetter$NonIdGetter.get(ReflectGetter.java:96)

at com.avaje.ebeaninternal.server.deploy.ReflectGetter$NonIdGetter.getIntercept(ReflectGetter.java:100)

at com.avaje.ebeaninternal.server.deploy.BeanProperty.getValueIntercept(BeanProperty.java:905)

... 18 more

Furthermore, when I try to setup the same inheritance structure using the Node class as concrete, I get a ClassCastException: node.NodeA cannot be cast to node.Node.

I haven't found much insight in looking at the source code, is my use case an impossibility in Ebean?

edge

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Jan 24, 2012, 2:55:41 AM1/24/12

to Ebean ORM

Hi Joseph,

I have a something working similar to what you want without any issue.
The exception above looks like you base class is abstract? Try
removing it and see if that helps. Otherwise please provide a test
case

Eddie

> com.avaje.ebean.common.AbstractBeanCollection.lazyLoadCollection(AbstractBe anCollection.java:147)

> at com.avaje.ebean.common.BeanList.init(BeanList.java:116)
> at com.avaje.ebean.common.BeanList.size(BeanList.java:408)
> at com.mainstream.exchange.data.Test.main(Test.java:20)
> Caused by: java.lang.RuntimeException: Not expecting this method to be
> called on [node.Node.children] as it is a NON ID property on an abstract
> class
> at
> com.avaje.ebeaninternal.server.deploy.ReflectGetter$NonIdGetter.get(Reflect Getter.java:96)
> at
> com.avaje.ebeaninternal.server.deploy.ReflectGetter$NonIdGetter.getIntercep t(ReflectGetter.java:100)
> at

> com.avaje.ebeaninternal.server.deploy.BeanProperty.getValueIntercept(BeanPr operty.java:905)

Joseph Conley

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Jan 24, 2012, 8:46:14 AM1/24/12

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Removing the abstract modifier did not help. Here is my test case:

@Entity

@Inheritance(strategy=InheritanceType.SINGLE_TABLE)

@DiscriminatorColumn(name="node_type_id")

public class Node {

@Id

public int id;

public String name;

@ManyToOne

@JoinColumn(name="parent_node_id")

public Node parent;

@OneToMany(mappedBy="parent")

public List<Node> children = new ArrayList<Node>();

//getters/setters

}

@Entity

@DiscriminatorValue("A")

public class NodeA extends Node {

}

@Entity

@DiscriminatorValue("B")

public class NodeB extends Node {

}

Data (stored in an H2 database):

ID	NAME	PARENT_NODE_ID	NODE_TYPE_ID
1	Root	null	A
2	Child	1	B
3	Child	1	A

After running the following code, I get the following error when trying to access the children of root (accessing the parent of a child works fine):

Node child = Ebean.find(Node.class, 2);

System.out.println(child); //works as expected

System.out.println(child.getParent()); //works as expected

Node root = Ebean.find(Node.class, 1);

System.out.println(root); //works as expected

System.out.println(root.getChildren().size()); //throws following error

Exception in thread "main" java.lang.RuntimeException: getIntercept children on [test.Node] type[test.NodeA$$EntityBean$asset] threw error.