Develop Reference

Multiple levels of cascading persists in Ebean

I have a model class which defines a list of children that are models of the same class. Persisting a new object with some initial children works fine, but when I have two or more levels of children Ebean does not seem to be able to handle it well. This seemed unexpected so I'm worried I made a mistake. At the same time I couldn't find any examples or mentions about multiple level persist cascades so my questions are:
Is there an error in my code, Is this even a supported feature or did I find a bug?
My model class:
#Entity
public class TestEntity extends Model {
#Id
private int id;
private String text;
#ManyToOne
private TestEntity parentEntity;
#OneToMany(cascade = CascadeType.ALL)
private List<TestEntity> childEntities;
...
}
My program:
TestEntity grandparent = new TestEntity();
grandparent.setText("grandparent");
TestEntity parent = new TestEntity();
parent.setText("parent");
TestEntity child = new TestEntity();
child.setText("child");
grandparent.setChildEntities(Collections.singletonList(parent));
parent.setChildEntities(Collections.singletonList(child));
grandparent.save();
I added logging for the sql statements and it is evident that the third insert didn't get the correct value for parent_entity_id. That row fails due to 0 not being a valid foreign key and the batch is reverted.
insert into test_entity (text, parent_entity_id) values ('grandparent',null);
insert into test_entity (text, parent_entity_id) values ('parent',1);
insert into test_entity (text, parent_entity_id) values ('child',0);
I'm using Play framework 2.7.3 with the ebean plugin version 5.0.2 and Ebean version 11.39

This is indeed a supported feature and the code snippet above is expected to persist all three entities.
There was a unit test added to verify that this is working correctly in the latest version of ebean.
In ebean 11.39 which is currently the latest supported by play framework the test fails. An easy workaround when using that version is to use Long instead of primitive int as ID for the models.
While not an answer to this specific question, it is good to be aware that these same symptoms also appear if the collections are set without using setters enhanced by ebean. I had some trouble using public fields and play enhancer .

Safe embedded entity with objectify

I have two entities.
#Entity
public class Recipe {
#Id
private Long id;
private List<Step> steps;
}
#Entity
public class Step {
#Id
private Long id;
private String instruction;
}
And the following Clound Endpoint
#ApiMethod(
name = "insert",
path = "recipe",
httpMethod = ApiMethod.HttpMethod.POST)
public Recipe insert(Recipe recipe) {
ofy().save().entities(recipe.getSteps()).now(); //superfluous?
ofy().save().entity(recipe).now();
logger.info("Created Recipe with ID: " + recipe.getId());
return ofy().load().entity(recipe).now();
}
I'm wondering how do I skip the step where I have to save the emebedded entity first. The Id of neither entity is set. I want objectify to automatically create those. But if don't save the embedded entity I get an exception.
com.googlecode.objectify.SaveException: Error saving com.devmoon.meadule.backend.entities.Recipe#59e4ff19: You cannot create a Key for an object with a null #Id. Object was com.devmoon.meadule.backend.entities.Step#589a3afb
Since my object structure will get a lot more complex, I need to find a way to skip this manual step.

I presume you are trying to create real embedded objects, not separate objects stored in the datastore and linked. Your extra save() is actually saving separate entities. You don't want that.
You have two options:
Don't give your embedded object an id. Don't give it #Entity and don't give it an id field (or at least eliminate #Id). It's just a POJO. 90% of the time, this is what people want with embedded objects.
Allocate the id yourself with the allocator, typically in your (non-default) constructor.
Assuming you want a true embedded entity with a real key, #2 is probably what you should use. Keep in mind that this key is somewhat whimsical since you can't actually load it; only the container object can be looked up in the datastore.
I suggest going one step further and never use automatic id generation for any entities ever. Always use the allocator in the (non-default) constructor of your entities. This ensures that entities always have a valid, stable id. If you always allocate the id before a transaction start, it fixes duplicate entities that can be created when a transaction gets retried. Populating null ids is just a bad idea all around and really should not have been added to GAE.

The concept of the embedded is that the embedded content is persisted inside the main entity.
Is this the behaviour you are trying to configure?
The default behaviour of a Collection (List) of #Entity annoted class is to refer them instead of embed them. As you current configuration, the List<Step> variable does not have any annotation to override the default configuration, which is a different entity related to another one.
The error you are getting is because Objectify, when it saves the recipe entity, is trying to get the key of each step to create the relationship (and save them in the recipe entity), but if the entity step is not saved yet on the datastore, does not have a key
If you are trying to persist the steps inside the recipe entity, you need to setup objectify like this
#Entity
public class Recipe {
#Id
private Long id;
private List<Step> steps;
}
public class Step {
private Long id;
private String instruction;
}
As you can see, I removed the #Id annotation (an embedded Entity does not require an ID because is inside another entity) and the #Entity from the Step class. With this configuration, Objectify save the step entities inside the recipe entity
Source: https://code.google.com/p/objectify-appengine/wiki/Entities#Embedded_Object_Native_Representation

Hibernate Inheritance.JOINED generated FK name

I am currently trying to use inheritance within Hibernate and came across InheritanceType.JOINED. I like the idea of concentrating all data in one table and sharing IDs rather than having duplicate columns in all the sub type tables (#MappedSuperClass). But Hibernate automatically generates indexes on my sub class tables on the id column like FK_idx3wiwdm8yp2qkkddi726n8o everytime I initialize my Hibernate singleton. I noticed that by hitting the 64 key limit on my MySQL Table as the names are generated differently on every startup.
What is the proper way to handle this? Can this be fixed by annotations? What else could I try?
I know that there are countless similar Questions on SO but haven't been able to identify one solving my specific problem.
I am not going to disable hbm2ddl.auto during dev mode.
I am using MyISAM. There are no actual Foreign Keys. This is why Hibernate generates default indexes, I think. Anyway, the problem would be identical with InnoDB and real Foreign Keys as the names would still be quite random. Or maybe Hibernate would actually check for existence in this case. I don't really see, why it does not do this on MyISAM tables.
As I hit similar problems before, the solution could also be to specify a name for that single-column index. But how?
Super Class: FolderItem
#Entity
#Inheritance(strategy = InheritanceType.JOINED)
public abstract class FolderItem implements Comparable<FolderItem>
{
#Id
#GeneratedValue
protected int id;
protected String name;
#OneToOne
#ForeignKey(name = "fkParent")
protected Folder parent;
...
}
Sub Class: Folder
#Entity
public class Folder extends FolderItem
{
#OneToMany(mappedBy = "parent")
#OrderBy(value = "sortOrder")
private List<FolderItem> children;
...
}
What I tried
add #Index to FolderItem.id - this created an index on the FolderItem table as one would expect, but didn't affect the Folder table
copy protected int id; to Folder and tried to add an #Index to it, which resulted in an Exception similar to "duplicate definition of ID"
add #Table(appliesTo = "Folder", indexes = { #Index(name = "fkId", columnNames = { "id" }) }) to Folder class, which actually created my specified index as expected, but still created it's own FK_9xcia6idnwqdi9xx8ytea40h3 which is identical to mine, except for the name

Try #PrimaryKeyJoinColumn(name = "foler_item_id") annotation for Folder class.

Persisting third-party classes with no ID's

Say I have the following Java class, which is owned by a vendor so I can't change it:
public class Entry {
private String user;
private String city;
// ...
// About 10 other fields
// ...
// Getters, setters, etc.
}
I would like to persist it to a table, using JPA 2.0 (OpenJPA implementation). I cannot annotate this class (as it is not mine), so I'm using orm.xml to do that.
I'm creating a table containing a column per field, plus another column called ID. Then, I'm creating a sequence for it.
My question is: is it at all possible to tell JPA that the ID that I would like to use for this entity doesn't even exist as a member attribute in the Entry class? How do I go about creating a JPA entity that will allow me to persist instances of this class?
EDIT
I am aware of the strategy of extending the class and adding an ID property it. However, I'm looking for a solution that doesn't involve extending this class, because I need this solution to also be applicable for the case when it's not only one class that I have to persist, but a collection of interlinked classes - none of which has any ID property. In such a scenario, extending doesn't work out.

Eventually, I ended up doing the following:
public class EntryWrapper {
#Id
private long id;
#Embedded
private Entry entry;
}
So, I am indeed wrapping the entity but differently from the way that had been suggested. As the Entry class is vendor-provided, I did all its ORM work in an orm.xml file. When persisting, I persist EntryWrapper.

I don't have much experience with JPA, but I wouldn't extend your base classes, instead I would wrap them:
public class PersistMe<T> {
#Id
private long id;
private T objToWrap;
public(T objToWrap) {
this.objToWrap = objToWrap;
}
}
I can't test it, if it doesn't work let me know so I can delete the answer.

Extend entity classes with composite keys in hibernate

In our company we have a strange database model which can't be modified because to many systems works with them. Up to know we have a straight java application which connects with hibernate to the database and loads the data. We have for each table one xml mapping file.
The strange thing about the database is that we do not have any primary keys. Most table have a unique index containing several columns.
Now we want to use an application server (jboss) and the ejb model. So I created a class like this:
#Entity
#Table (name = "eakopf_t")
public class Eakopf implements Serializable {
#Embeddable
public static class EakopfId implements Serializable {
private String mandant;
private String fk_eakopf_posnr;
// I removed here the getters and setters to shorten it up
}
#Id
private EakopfId id;
private String login;
// I removed the getters and setters here as well
}
This works perfect.
Because our customers have different versions of the database schema I thought about extending this class on each database release change. So each interface we create with java can decide which version of the table will be used.
Here is the extended table class
#Entity
#Table (name = "eakopf_t")
public class Eakopf6001 extends Eakopf implements Serializable {
private String newField;
// getters and setters
}
If I use Eakopf (the base version) it is working if I do something like that:
EakopfId id = new EakopfId();
id.setMandant("001");
id.setFk_eakopf_posnr("ABC");
Eakopf kopf = (Eakopf) em.find(Eakopf.class, id);
But if I do this:
EakopfId id = new EakopfId();
id.setMandant("001");
id.setFk_eakopf_posnr("ABC");
Eakopf6001 kopf = (Eakopf6001) em.find(Eakopf6001.class, id);
this exception occues
javax.ejb.EJBException: javax.persistence.PersistenceException:
org.hibernate.WrongClassException: Object with id:
de.entity.Eakopf$EakopfId#291bfe83 was not of the specified subclass:
de.entity.Eakopf (Discriminator: null)
Does anybody has an idea?
many greetings,
Hauke

Doing what you did means to Hibernate that you're storing two different kinds of entities in a single table. This is possible is you use a discriminator column. But if I understand correctly, you just want one kind of entity in the table : Eakopf6001. In this case, its base class should be annotated with #MappedSuperClass, not with #Entity.
I would suggest creating a class annotated with #MappedEntity (let's call it BaseEakopf), and two entities: EaKopf and EaKopf6001, each with their set of additional fields. Include one of the other of the entities in the list of mapped classes, depending on which one you want to use.
My personal opinion is that if you have multiple versions of your app, they should use the same entities, but with different fields. Your version control system would take care of these multiple versions, rather than your source code (i.e. have one set of source files per version of the app, rather than one single set of source files for all the possible versions).