Ok, the problem only shows up if the target property in the entity uses inheritance. In the above example the OPS_ZONES is twice in OPS_TOPOLOGY (namely SRC and DST) and OPS_ZONES itself has some subclasses.

In BeanPropertyAssocOne this forces the ebean to add the join, later then in SqlTreeNodeBean the join gets added again for each element in the "children" array.

I've extended the TestInheritInsert by a testQuery() method.

This will show two bugs:

1) The VehicleDriver will not insert due to an NullPointerException regarding gettig the id.
2) If 1 is fixed, it will show the duplicate added join stuff due to the inheritance of "vehicle"

The NPE for 1:
java.lang.RuntimeException: get id on [com.avaje.tests.model.basic.Vehicle] type[com.avaje.tests.model.basic.Car] threw error.
at com.avaje.ebean.server.deploy.BeanProperty.getValue(BeanProperty.java:648)
at com.avaje.ebean.server.deploy.id.ImportedIdSimple.bind(ImportedIdSimple.java:103)
at com.avaje.ebean.server.persist.dmlbind.BindableAssocOne.dmlBind(BindableAssocOne.java:75)
at com.avaje.ebean.server.persist.dmlbind.BindableList.dmlBind(BindableList.java:62)
at com.avaje.ebean.server.persist.dml.InsertMeta.bind(InsertMeta.java:152)
at com.avaje.ebean.server.persist.dml.InsertHandler.bind(InsertHandler.java:124)
at com.avaje.ebean.server.persist.dml.DmlBeanPersister.execute(DmlBeanPersister.java:96)
at com.avaje.ebean.server.persist.dml.DmlBeanPersister.insert(DmlBeanPersister.java:74)
at com.avaje.ebean.server.persist.DefaultPersistExecute.executeInsertBean(DefaultPersistExecute.java:94)
at com.avaje.ebean.server.core.PersistRequestBean.executeNow(PersistRequestBean.java:341)
at com.avaje.ebean.server.core.PersistRequestBean.executeOrQueue(PersistRequestBean.java:371)
at com.avaje.ebean.server.persist.DefaultPersister.insert(DefaultPersister.java:256)
at com.avaje.ebean.server.persist.DefaultPersister.save(DefaultPersister.java:202)
at com.avaje.ebean.server.persist.DefaultPersister.saveRecurse(DefaultPersister.java:172)
at com.avaje.ebean.server.persist.DefaultPersister.save(DefaultPersister.java:161)
at com.avaje.ebean.server.core.DefaultServer.save(DefaultServer.java:1442)
at com.avaje.ebean.server.core.DefaultServer.save(DefaultServer.java:1432)
at com.avaje.ebean.Ebean.save(Ebean.java:522)
at com.avaje.tests.inheritance.TestInheritInsert.testQuery(TestInheritInsert.java:36)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:40)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at com.intellij.rt.execution.application.AppMain.main(AppMain.java:90)
Caused by: java.lang.NullPointerException
at com.avaje.ebean.server.deploy.BeanProperty.getValue(BeanProperty.java:640)
... 39 more

As a workaround to get faster to 2 one can comment the line
driver.setVehicle(car)

Then the sql looks like this:

select v.id c0, v.name c1, v.cretime c2, v.updtime c3, vv.DTYPE c4, v.vehicle_id c5
from vehicle_driver v
left outer join vehicle vv on vv.id = v.vehicle_id
left outer join vehicle vv on vv.id = v.vehicle_id
where vv.license_number = ?

my project was not cleanly compiled. sorry.

by moving the addJoin from deploy.TableJoin into the DbSqlContext which than can keep track of which joins have been added I fixed it here.

I'll send the patch for review to Rob using email.

when using the maven build. Seems than subclassing is used instead of weaving and a bug is uncovered here? Building ebean using weaving with my IDE the NPE does not happen.

Yes, the NPE is a bug. The ManyToOne is an inheritance hierarchy with the @Id property on an abstract class (the root of the inheritance tree is abstract). So this is the cause for the NPE - I'll log that as a separate bug.

Logged the NPE as http://www.avaje.org/bugdetail-166.html

Fixed in HEAD.