Category Archives: Persistence

Configuring persistence of fields/properties using TypeConverters with JDO

JPA 2.1 allows a user to specify a converter on the value of a field/property for how it is persisted in the datastore. The way we implement that in DataNucleus is to have the JPA converter as a wrapper to … Continue reading

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Persistence to Neo4j graph datastores

Whilst DataNucleus JDO/JPA already supported persistence and querying of objects to/from RDBMS (all variants), ODBMS (NeoDatis), Documents (XML, Excel, ODF), Web (JSON), Document-based (MongoDB), Map-based (HBase, AppEngine, Cassandra), as well as others like LDAP and VMForce, it was clear that … Continue reading

Posted in JDO, JDOQL, JPA, JPQL, Neo4j, Persistence | 7 Comments

Performance, benchmarking

Every so often some individual or group decides they’re going to “invent” a new benchmark. They ignore all that have been done before (like PolePos) maybe due to NotInventedHereSyndrome, or maybe due to “oh someone who helped write that was … Continue reading

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JDO Typesafe Queries : Part 2 – Expressions

Continuing on from the previous post, in order to be able to express components of a query in a Java style we need to represent all fields/properties/parameters/variables as expressions. The type of the field/property/parameter/variable determines its expression type. Let’s take … Continue reading

Posted in JDO, JDOQL, Persistence | 11 Comments

Persisting multisets (bags) with DataNucleus

A multiset is a set where you can have a particular object multiple times in the set (a normal java.util Set will remove dups). This is also known by some as a “bag”. Google’s Collections library has such a container … Continue reading

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AccessPlatform 2.0 will arrive soon

… just until the 9th January 2010 to wait. The result of 10 months of restructuring and extensions to DataNucleus, extending the capabilities and simplifying the process of adding on new datastore support for many things.

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As mentioned earlier DataNucleus querying capabilities are being progressively rewritten, making use of a “generic” query compilation. In the previous post I mentioned a new implementation of JDOQL. This now implements the vast majority of querying capabilities required with one … Continue reading

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