Re: [hibernate-dev] Question about substituting IDs in Hibernate OGM

[Haswell, Josiah D]

Perfect.  That worked—thanks for the help!

I’ve made some pretty good progress—you can save entities and some 
associations, and retrieve some properties lazily.  Unfortunately, I’m having a 
bit of trouble with getting access to all of the type information I need.


In particular, say you have the hierarchy:


@Inheritance(strategy = InheritanceType.TABLE_PER_CLASS)  (1)
@Entity
@Table(name = “persistable”)
Public class Persistable {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
Long id;

@Basic
String persistableName;


}


@Entity
@Table(“person_table”)
Public class Person extends Persistable {

@Basic
@Column(name = “first_name”)
String firstName;

@Basic
@Column
String lastName;

}

I need to generate the schema:

:persistable/persistableName

:Person/first_name
:Person/lastName

And access it from a few contexts.


Schema Definition

When generating the schema, I need to be able to get the table name, which I 
was able to from the EntityPersisters available in SessionFactoryImpl.  From 
there, I needed to be able to get each property on each class, its type, and 
its alias (as defined by @Column), which I couldn’t figure out how to do.  I 
looked through both the EntityMetamodel and the ClassMetamodels on each 
persister, but it wasn’t clear how to get that.

Looking in the ClassMetadata, I found the property names, but that included all 
of the properties for all of the linear supertypes of the associated entity.
Looking at the EntityMetamodel, I found I could get all of the properties, but 
I couldn’t figure out how to filter out the properties declared in the current 
entity type.

I ended up scanning the annotations again to get the information I needed to 
generate the schema, which doesn’t seem like a good solution.


Now, I’m running into the same problem retrieving a tuple:



public Tuple getTuple(EntityKey k, TupleContext c) {
final Long id = getOrThrowUnexpectedId(k);
final Entity entity = retrieveEntity(id);
return new Tuple(new LazyEntityBackedTupleSnapshot(entity, tupleContext));
}


public class LazyEntityBackedTupleSnapshot implements TupleSnapshot {
final Entity entity;
final TupleContext context;
//constructor, etc.

public Object get(String column) {
return entity.get(column);

}


}


Now, the problem is, say the entity that I retrieved was a Person.  If I call 
p.getPersistableName() , then entity.get(column) needs to be
Entity.get(“:persistable/persistableName”) to get the value.  I could search 
through the linear supertypes of the current type if I could get it.  I notice 
that the actual TupleContext that I’m getting has an OptionsContextImpl with an 
entity type that I can use to search for the appropriate entity type, but 
that’s private, and I don’t want to use reflection to get it.

I’m sure I’m just missing some cool feature of OGM here, and couldn’t find it 
looking through the other implementations.  Any additional help would be 
fantastic.

Thanks!



From: gunnar.morl...@googlemail.com [mailto:gunnar.morl...@googlemail.com] On 
Behalf Of Gunnar Morling
Sent: Wednesday, February 11, 2015 12:43 AM
To: Haswell, Josiah D
Cc: hibernate-dev@lists.jboss.org
Subject: Re: [hibernate-dev] Question about substituting IDs in Hibernate OGM

Hi Josiah,

It's great to hear that you are working an a backend for Hibernate OGM!

Regarding ids, it should work for you if they are mapped using the IDENTITY 
strategy:

    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    Long id;

This causes the Hibernate ORM engine to read back the id value generated by the 
datastore upon insertion. To make it work, your GridDialect for OGM needs to 
implement the IdentityColumnAwareGridDialect facet [1]. You can check out the 
MongoDB dialect for an example.

If this works and this kind of id generation is the only one which is useful 
for Datomic (i.e. table/sequence strategies don't make any sense), you may 
validate mapped entities by means of a SchemaDefiner [2] (an experimental 
contract of OGM). An example is CouchDBSchemaDefiner.

Let us know how it goes or in case you run into any other issues.

--Gunnar

[1] 
https://github.com/hibernate/hibernate-ogm/blob/master/core/src/main/java/org/hibernate/ogm/dialect/identity/spi/IdentityColumnAwareGridDialect.java
[2] 
https://github.com/hibernate/hibernate-ogm/blob/master/couchdb/src/main/java/org/hibernate/ogm/datastore/couchdb/impl/CouchDBSchemaSchemaDefiner.java



2015-02-11 2:40 GMT+01:00 Haswell, Josiah D 
<josiah.hasw...@ca.com<mailto:josiah.hasw...@ca.com>>:
Hi folks,

I'm creating a Hibernate OGM implementation for Datomic, and I have a question 
about IDs.

Say I have the entity

@Entity
public class Person {
@Id
@GeneratedValue
Long id;


}

In Datomic, you have to assign a temporary ID before submitting the 
transaction.  Datomic will then return the actual persistence ID after the 
transaction has completed.  My question is, how can I get the actual ID back 
into the entity?

Thanks!

Josiah
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