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TODO:
This section is a work in progress, if you find something that does not work as expected, let us know and we will update it (and fix the problem of course).
Pretty much all entity related constructs should work out of the box in Hibernate OGM.
@Entity, @Table, @Column,
@Enumarated, @Temporal, @Cacheable
and the like will work as expected.
If you want an example,
check out Chapter 2, Getting started with Hibernate OGM or the documentation of Hibernate ORM.
Let’s concentrate of the features that differ
or are simply not supported by Hibernate OGM.
The various inheritance strategies are not supported by Hibernate OGM,
only the table per concrete class strategy is used.
f This is not so much a limitation
but rather an acknowledgment of the dynamic nature of NoSQL schemas.
If you feel the need to support other strategies,
let us know (see Section 1.2, “How to contribute”).
Simply do not use @Inheritance nor @DiscriminatorColumn.
Secondary tables are not supported by Hibernate OGM at the moment. If you have needs for this feature, let us know (see Section 1.2, “How to contribute”).
All SQL related constructs as well as HQL centered mapping are not supported in Hibernate OGM. Here is a list of feature that will not work:
All standard JPA id generators are supported: IDENTITY, SEQUENCE, TABLE and AUTO. If you need support for additional generators, let us know (see Section 1.2, “How to contribute”). We recommend you use a UUID based generator as this type of generator allows maximum scalability to the underlying data grid as no cluster-wide counter is necessary.
Example 6.1. Using a UUID generator
@Entity
public class Breed {
@Id @GeneratedValue(generator = "uuid")
@GenericGenerator(name="uuid", strategy="uuid2")
public String getId() { return id; }
public void setId(String id) { this.id = id; }
private String id;
public String getName() { return name; }
public void setName(String name) { this.name = name; }
private String name;
}
Most Java built-in types as supported at this stage.
However, custom types (@Type) are not supported.
A few types are supported natively (ie serialized as is in the tuple data structure):
This list is subject to change and specifically be reduced to a smaller set of core types.
For non basic Java types support, OGM stores the data of the object as a String in the data store. Serialisation to a String value is done with cross platform compatibility in mind when required.
All association types are supported (@OneToOne,
@OneToMany, @ManyToOne, @ManyToMany).
Likewise, all collection types are supported (Set, Map,
List).
The way Hibernate OGM stores association information is however quite different
than the traditional RDBMS representation.
Check Section 3.2, “How is data persisted” for more information.
Keep in mind that collections with many entries won’t perform very well in Hibernate OGM (at least today) as all of the association navigation for a given entity is stored in a single key. If your collection is made of 1 million elements, Hibernate OGM stores 1 million tuples in the association key.