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Welcome to Jenmo, a Java project built on top of JPA. It is an implementation of a graph-oriented domain model in order to benefit the advantages of a unified schema in relational database. It is available under the terms of the Apache Software License.
The name Jenmo results from the contraction of two words: Gen-eric and Mo-del (‘J’ is for Java). It is a project made of about 80 classes and 5000 lines of code.
Over the 80 project classes, only 9 have a correspondence in datastore: they form the graph-oriented domain model and the generic shema.
In substance, graph vertices are modelized by Node entities, and graph links by Edge entities. Note that this is a directed graph i.e. edges have orientation.
A Node holds values with NodeProperty and NodeField entities depending of the nature of the property values.
A Node is described by metadata modelized by NodeType and Property.
Below is a very simple code example:
// Create Metadata (UserConstants is enum)
Property login = Property.newInstance(UserConstants.LOGIN.name());
Property email = Property.newInstance(UserConstants.EMAIL.name());
Property account = Property.newInstance(UserConstants.ACCOUNT.name());
NodeType typeUser = NodeType.newInstance(TypeConstants.USER.name(), login, email, account);
// Create Node user
Node aUser = Node.newRoot(typeUser, "aUser");
// Set property values to user
aUser.setProperty(login, "aUserLogin");
aUser.setProperty(email, "aUser@company.com");
// Create Node child
Node aUserChild = Node.newOutput(aUser, typeUser, "aUserChild");
// Set property values to child (simple ones)
aUserChild.setProperty(login, "aUserChildLogin");
aUserChild.setProperty(email, "aUserChild@company.com");
// Set property values to child (complex ones)
Map<String, BigDecimal> accounts = aUserChild.getProperties(account,
Descriptors.mapForProps(String.class, BigDecimal.class));
accounts.put("bnp", new BigDecimal(75000.98));
accounts.put("lpb", new BigDecimal(25022.25));
// Persist: note that we only need to explicitly persist a single root of the
// object graph, since we have the "cascade" annotation on all the relations
em.persist(aUser);
// Commit the transaction, which will cause the entity to
// be stored in the database
em.getTransaction().commit();
The main purpose with Jenmo was to achieve a unified schema in database. Key points of a unified schema are (non exhaustive list): avoid complicated SQL migration scripts after changes in the domain-model, facilitate the use of an ETL if needed, make easier exports of domain-model sub parts either with SQL scripts or in Java, facilitate Node deletion in database…
The Jenmo main functionalities are listed below:
- cache system using SoftReference
- extensible configuration system
- localised messages and exceptions
- JPA EntityManager lifecycle management (session-per-thread model or not)
- generic DAO to provide specific data-access operations
- generic Adapters to convert Node relationships into interfaces expected by client code
- splitted blobs in datastore with the opportunity to extract sub-parts only
- listener system to listen for blob extractions from datastore
- simple API for manipulations of multidimensional arrays
- Jenmo at github.
At the moment, Jenmo has been used with MySQL 5.0, PostgreSQL 8.3, OpenJPA 2.0 and EclipseLink 2.0.0. Tests should begin shortly with Hibernate