Hibernate Object/Grid Mapper (OGM) is a persistence engine providing Java Persistence (JPA) support for NoSQL datastores. It reuses Hibernate ORM’s object life cycle management and (de)hydration engine but persists entities into a NoSQL store (key/value, document, column-oriented, etc) instead of a relational database. It reuses the Java Persistence Query Language (JP-QL) as an interface to querying stored data.
The project is now fairly mature when it comes to the storage strategies. And the feature set is sufficient to be used in your projects. We do have however much bigger ambitions than a simple object mapper. Many things are on the roadmap (more NoSQL, query, denormalization engine, etc). If you feel a feature is missing, report it to us. If you want to contribute, even better!
Hibernate OGM is released under the LGPL open source license.
Note
The future of this project is being shaped by the requests from our users. Please give us feedback on
- what you like
- what you don’t like
- what is confusing
- what you are missing as a feature
Check Section 1.2, “How to contribute” on how to contact us.
Tip
We worked hard on this documentation but we know it is far from perfect. If you find something confusing or feel that an explanation is missing, contact us in one of the following ways:
- post on Hibernate OGM’s forum.
- open bug reports in JIRA
- propose improvements on the development mailing list
- join us on IRC to discuss developments and improvements
(
#hibernate-devonfreenode.net; you need to be registered on freenode: the room does not accept "anonymous" users).
Hibernate OGM:
- offers a familiar programming paradigm (JPA) to deal with NoSQL stores
- moves model denormalization from a manual imperative work to a declarative approach handled by the engine
- encourages new data usage patterns and NoSQL exploration in more "traditional" enterprises
- helps scale existing applications with a NoSQL front end to a traditional database
NoSQL can be very disconcerting as it is composed of many disparate solutions with different benefits and drawbacks. Speaking only of the main ones, NoSQL is at least categorized in four families:
- graph oriented databases
- key/value stores: essentially Maps but with different behaviors and ideas behind various products (data grids, persistent with strong or eventual consistency, etc)
- document based datastores: contains as value semi-structured documents (think JSON)
- column based datastores
Each have different benefits and drawbacks and one solution might fit a use case better than an other. However access patterns and APIs are different from one product to the other.
Hibernate OGM is not expected to be the Rosetta stone used to interact with all NoSQL solution in all use cases. But for people modeling their data as a domain model, it provides distinctive advantages over raw APIs and has the benefit of providing an API and semantic known to Java developers. Reusing the same programmatic model and trying different (No)SQL engines will hopefully help people to explore alternative datastores.
Hibernate OGM also aims at helping people scale traditional relational databases by providing a NoSQL front-end and keeping the same JPA APIs and domain model.
Today, Hibernate OGM does not support all of these goals. Here is a list of what we have:
- store data in key/value stores (Infinispan’s datagrid and Ehcache)
- store data in document stores (MongoDB and CouchDB - the latter in preview)
- store data in graph databases (Neo4J)
- Create, Read, Update and Delete operations (CRUD) for entities
- polymorphic entities (support for superclasses, subclasses etc).
- embeddable objects (aka components)
- support for basic types (numbers, String, URL, Date, enums, etc)
- support for associations
- support for collections (Set, List, Map, etc)
- support for JP-QL queries (not arbitrary joins though)
- support for mapping native queries results to managed entities
- support for Hibernate Search’s full-text queries
- and generally, support for JPA and native Hibernate ORM API support
In short, a perfectly capable Object Mapper for multiple popular NoSQL datastores.
As Hibernate OGM is a rather young project, some parts of it may be marked as experimental.
This may affect specific APIs or SPIs (e.g. the case for the SchemaInitializer SPI contract at the moment),
entire dialects (this is the case for the CouchDB dialect at the moment)
or deliverables.
Experimental APIs/SPIs are marked via the @Experimental annotation.
Experimental dialects make that fact apparent through their datastore name (e.g. "COUCHDB_EXPERIMENTAL")
and experimental deliverables use the "experimental" artifact classifier.
If a certain part is marked as experimental it may undergo backwards-incompatible changes in future releases. E.g. API/SPI methods may be altered, so that code using them needs to be adapted as well. For experimental dialects the persistent format of data may be changed, so that a future version of such dialect may not be able to read back data written by previous versions. A manual update of the affected data may be thus required. Experimental deliverables should be used with special care, as they are work in progress. You should use them for testing but not production use cases.
But most of our dialects are mature, so don’t worry ;)
Here are a few areas where Hibernate OGM can be beneficial:
- need to scale your datastore up and down rapidly (via the underlying NoSQL datastore capability)
- keep your domain model independent of the underlying datastore technology (RDBMS, Infinispan, NoSQL)
- explore the best tool for the use case
- use a familiar JPA front end to your datastore
- use Hibernate Search full-text search / text analysis capabilities and store the data set in an scalable datastore
These are a few ideas and the list will grow as we add more capabilities to Hibernate OGM.