java.lang.InstantiationException when trying to find a class that extends a abstract class.

I created something like this below:

@Entity public abstract class myabs { }

public class child extends myabs { }

when I tried to find using the code like below:

new AnonymousClass { public void find() {

Mongo mongo ...
Morphia mor ...
...                      

List<ObjectId>ids = dao.findIds();
Model model = null;
for(ObjectId id : ids)
  model = dao.get(id);

} }

I got the exception:

java.lang.RuntimeException: java.lang.RuntimeException at org.mongodb.morphia.mapping.EmbeddedMapper.fromDBObject(EmbeddedMapper.java:161) at org.mongodb.morphia.mapping.Mapper.readMappedField(Mapper.java:604) at org.mongodb.morphia.mapping.Mapper.fromDb(Mapper.java:584) at org.mongodb.morphia.mapping.Mapper.fromDBObject(Mapper.java:294) at org.mongodb.morphia.query.MorphiaIterator.convertItem(MorphiaIterator.java:71) at org.mongodb.morphia.query.MorphiaIterator.processItem(MorphiaIterator.java:58) at org.mongodb.morphia.query.MorphiaIterator.next(MorphiaIterator.java:53) at org.mongodb.morphia.query.QueryImpl.get(QueryImpl.java:408) at org.mongodb.morphia.DatastoreImpl.get(DatastoreImpl.java:606) at org.mongodb.morphia.dao.BasicDAO.get(BasicDAO.java:165) at controllers.CityController$1$1.invoke(CityController.java:77) at controllers.CityController$1$1.invoke(CityController.java:37) at play.core.j.JavaWebSocket$$anonfun$webSocketWrapper$1$$anonfun$apply$1$$anonfun$apply$2$$anonfun$apply$3.apply(JavaWebSocket.scala:43) at play.core.j.JavaWebSocket$$anonfun$webSocketWrapper$1$$anonfun$apply$1$$anonfun$apply$2$$anonfun$apply$3.apply(JavaWebSocket.scala:43) at scala.collection.Iterator$class.foreach(Iterator.scala:727) at scala.collection.AbstractIterator.foreach(Iterator.scala:1157) at scala.collection.IterableLike$class.foreach(IterableLike.scala:72) at scala.collection.AbstractIterable.foreach(Iterable.scala:54) at play.core.j.JavaWebSocket$$anonfun$webSocketWrapper$1$$anonfun$apply$1$$anonfun$apply$2.apply(JavaWebSocket.scala:43) at play.core.j.JavaWebSocket$$anonfun$webSocketWrapper$1$$anonfun$apply$1$$anonfun$apply$2.apply(JavaWebSocket.scala:43) at play.api.libs.iteratee.Iteratee$$anonfun$foreach$1.apply(Iteratee.scala:198) at play.api.libs.iteratee.Iteratee$$anonfun$foreach$1.apply(Iteratee.scala:198) at play.api.libs.iteratee.Iteratee$$anonfun$fold$1$$anonfun$apply$1.apply(Iteratee.scala:38) at play.api.libs.iteratee.internal$.eagerFuture(package.scala:27) at play.api.libs.iteratee.Iteratee$$anonfun$fold$1.apply(Iteratee.scala:38) at play.api.libs.iteratee.Iteratee$$anonfun$fold$1.apply(Iteratee.scala:38) at play.api.libs.iteratee.Iteratee$$anonfun$1.apply(Iteratee.scala:57) at play.api.libs.iteratee.Iteratee$$anonfun$1.apply(Iteratee.scala:57) at scala.concurrent.impl.Future$PromiseCompletingRunnable.liftedTree1$1(Future.scala:24) at scala.concurrent.impl.Future$PromiseCompletingRunnable.run(Future.scala:24) at scala.concurrent.forkjoin.ForkJoinTask$AdaptedRunnableAction.exec(ForkJoinTask.java:1361) at scala.concurrent.forkjoin.ForkJoinTask.doExec(ForkJoinTask.java:260) at scala.concurrent.forkjoin.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1339) at scala.concurrent.forkjoin.ForkJoinPool.runWorker(ForkJoinPool.java:1979) at scala.concurrent.forkjoin.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:107) Caused by: java.lang.RuntimeException at org.mongodb.morphia.mapping.DefaultCreator.createInst(DefaultCreator.java:127) at org.mongodb.morphia.mapping.DefaultCreator.createInstance(DefaultCreator.java:31) at org.mongodb.morphia.mapping.DefaultCreator.createInstance(DefaultCreator.java:42) at org.mongodb.morphia.mapping.DefaultCreator.createInstance(DefaultCreator.java:54) at org.mongodb.morphia.mapping.EmbeddedMapper.readMapOrCollectionOrEntity(EmbeddedMapper.java:246) at org.mongodb.morphia.mapping.EmbeddedMapper.readCollection(EmbeddedMapper.java:191) at org.mongodb.morphia.mapping.EmbeddedMapper.fromDBObject(EmbeddedMapper.java:135) … 34 more Caused by: java.lang.InstantiationException at sun.reflect.InstantiationExceptionConstructorAccessorImpl.newInstance(InstantiationExceptionConstructorAccessorImpl.java:30) at java.lang.reflect.Constructor.newInstance(Constructor.java:513) at org.mongodb.morphia.mapping.DefaultCreator.createInst(DefaultCreator.java:125) … 40 more

[evanchooly]

I’m assuming this worked for you. I’ll close this in a few days if I haven’t heard back.

[evanchooly]

That abstract class is going to break things because it can’t be instantiated so it needs to be not abstract. To fix your queries to correctly return the Child class do something like this:

datastore.createQuery(Child.class).filter("className = ", Child.class.getName()) …

That should resolve both issues for you.

On Tue, Oct 15, 2013 at 8:25 PM, Abraão Isvi [e-mail]:

Here my code below (simplified and with some changes), I did not have time to write another code, but maybe friday I can try it.

Recently I changed the abstract class to not abstract but that created another problem, now when I fetch the model it brings me the father class, not instantiating the child classes.

For example:

public abstract class Father { … }

public class Child extends Father { … }

public class Model { List items; … }

Where the error occurs:

public class MyController extends Controller{

public static WebSocket<JsonNode> map() { return new WebSocket<JsonNode>() {

    public void onReady(WebSocket.In<JsonNode> in, final WebSocket.Out<JsonNode> out) {

        // For each event received on the socket,
        in.onMessage(new Callback<JsonNode>() {

            @Override
            public void invoke(JsonNode message) throws Throwable {
                try {

                    String name = message.get("name").asText();
                    if(name.equalsIgnoreCase(MyConstants.SHOW_MAP_MESSAGE_NAME)) {
                        getModel(message, out);
                    }
                } catch (Exception e) {
                    e.printStackTrace();

                    ObjectMapper mapper = new ObjectMapper();
                    out.write(mapper.valueToTree("erro"));
                }

            }
        });

        // When the socket is closed.
        in.onClose(new Callback0() {

            @Override
            public void invoke() throws Throwable {
                // TODO Auto-generated method stub

            }
        });

    }
  };

}

private static void getModel(JsonNode message, final WebSocket.Out<JsonNode> out) throws Exception {

Mongo mgc = UtilRepository.getMongoClient();
Morphia mor = UtilRepository.getMorphia();

ModelRepository repo = new ModelRepository(mgc, mor);

List<ObjectId>ids = repo.findIds();
Model model = null;
for(ObjectId id : ids) {
     model = repo.get(id);
}

ObjectMapper mapper = new ObjectMapper();
out.write(mapper.valueToTree(model));

}

}

I hope this helps.

— Reply to this email directly or view it on GitHubhttps://github.com/mongodb/morphia/issues/538#issuecomment-26384131 .