Category Archives: JDOQL

JDO 3.2 JDOQLTypedQuery : improvements relative to DN extension

Now that JDO 3.2 standardises the “typed query” mechanism that we prototyped in DataNucleus v3.x and v4.0/v4.1 it is worth mentioning the additions to the API that are present in the JDO 3.2 variant. StringExpression This has gained the following … Continue reading

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JDO 3.2 JDOQLTypedQuery

JDO 3.2 is now standardising what we initially developed as a DataNucleus extension for JDO querying, namely typesafe queries. In DataNucleus upto and including v4.1 it was referred to as JDOQL Typesafe Query, and in JDO 3.2 (DataNucleus v4.2+) it … Continue reading

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JDO : querying between classes without relation

Let’s say we have the following classes and are using RDBMS for persistence public class Country { long id; String name; } public class Region { long id; String name; Long countryId; } public class District { long id; String … Continue reading

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Want to assist in the development of JDO 4.0?

We have, since 2006, been reliant on the Apache JDO project to push forward the JDO standard. Politics have finally become too much for this arrangement, with Oracle involving lawyers to prohibit progress, and the Apache organisation not being as … 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

JDO Typesafe .vs. JPA Criteria

JPA2 introduced its “Criteria” queries, providing an API for typesafe query generation without the need to hardcode field names etc in queries; it built on the approach of Hibernate Criteria. DataNucleus includes a proposal for JDO “Typesafe” queries. It takes … Continue reading

Posted in Criteria, JDO, JDOQL, JPA, LINQ, Typesafe | 9 Comments

JDO Typesafe Queries : Part 3 – Examples

In two previous blog posts, we introduced the idea of having a typesafe refactor friendly API for queries for JDO, and then described typical expression types necessary to achieve that. In this blog post we take that a step further, … Continue reading

Posted in JDO, JDOQL, JPA, LINQ, Typesafe | 15 Comments

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

JDO Typesafe Refactorable Queries

One of the primary drawbacks with current JDO queries is that they are string-based, so you are hardcoding field names etc. When you refactor a (model) class, the field names are left unchanged, so the query no longer works. Some … Continue reading

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JDOQL2 status

Some time ago I started a new implementation of JDOQL for RDBMS, to replace the legacy (TJDO) JDOQL implementation. The legacy implementation had problems with generation of SQL for many queries, particularly involving “contains”, “!contains” and use of unbound variables. … Continue reading

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