Datastore Connection

DataNucleus supports 2 modes of operation of neodatis - file-based, and client-server based. In order to do so and to fit in with the JDO/JPA APIs we have defined the following means of connection.

The following persistence properties will connect to a file-based Neodatis running on your local machine

datanucleus.ConnectionURL=neodatis:file:neodatisdb.odb

Replacing "neodatis.odb" by your filename for the datastore, and can be absolute OR relative.

The following persistence properties will connect to embedded-server-based NeoDatis running with a local file

datanucleus.ConnectionURL=neodatis:server:{my_neodatis_file}
datanucleus.ConnectionUserName=
datanucleus.ConnectionPassword=

The filename {my_neodatis_file} can be absolute OR relative.

The following persistence properties will connect as a client to a TCP/IP NeoDatis Server

datanucleus.ConnectionURL=neodatis:{neodatis_host}:{neodatis_port}/{identifier}
datanucleus.ConnectionUserName=
datanucleus.ConnectionPassword=

Neodatis doesn't itself use such URLs so it was necessary to define this DataNucleus-specific way of addressing Neodatis.

So you create your PersistenceManagerFactory or EntityManagerFactory with these properties. Thereafter you have the full power of the JDO or JPA APIs at your disposal, for your NeoDatis datastore.

Queries

AccessPlatform allows you to query the objects in the datastore using the following

• JDOQL - language based around the objects that are persisted and using Java-type syntax
• JPQL - language based around the objects that are persisted and using SQL-like syntax
• Native - NeoDatis' own type-safe query language
• Criteria - NeoDatis' own Criteria query language

Queries : NeoDatis Native Queries

NeoDatis provides its own "native" query interface, and if you are using the JDO API you can utilise this for querying. To take a simple example

// Find all employees older than 31
Query q = pm.newQuery("Native", new NativeQuery()
    {
        public boolean match(Object e)
        {
            if (!(e instanceof Employee))
            {
                return false;
            }
            return ((Employee)e).getAge() >= 32;
        }
        public Class getObjectType()
        {
            return Employee.class;
        }
    });

List results = (List)q.execute();

So we are utilising the JDO API to generate a query and passing in the NeoDatis "NativeQuery".

Queries : NeoDatis Criteria Queries

NeoDatis provides its own "criteria" query interface, and if you are using the JDO API you can utilise this for querying. To take a simple example

// Find all employees older than 31
Query q = pm.newQuery("Criteria", new CriteriaQuery(Employee.class, Where.ge("age", 32)));

List results = (List)q.execute();

So we are utilising the JDO API to generate a query and passing in the NeoDatis "CriteriaQuery".

Known Limitations

The following are known limitations of the current implementation

• NeoDatis doesn't have the concept of an "unloaded" field and so when you request an object from the datastore it comes with its graph of objects. Consequently there is no "lazy loading" and the consequent impact that can have on memory utilisation.