Database Schema Definition in Java

As explained in the Java Quick Start, the JNI uses the Java class syntax, with annotations. At run-time, Java reflection is used to discover the classes with their annotations and build up an eXtremeDB database dictionary. Note that the annotation @Persistent() marks a Java class to be managed by the eXtremeDB runtime in an In-Memory Database. (If the database is to be stored on persistent storage, the annotation modifier @Persistent(disk=true) must be added.)

Please refer to the JNI Schema Reference Guide for detailed explanations of the usage of JNI annotations to define the Database, Class, Field and Index characteristics.

Persistent Databases

For persistent database applications the database classes are defined exactly as for in-memory databases except for the class annotation @Persistent(disk=true) for all classes that will be stored on persistent media. For example:

 
    @Persistent(disk=true)
    class Obj
    {
        public int i4;
    };
     

If all classes are to be stored on persistent media, an alternative is to use the Database.Parameters property diskClassesByDefault for the parameters passed to the Database method open(). For example:

 
    Database.Parameters parameters = new Database.Parameters();
    parameters.classes = new Class[]{Obj.class};
    ...
    parameters.diskClassesByDefault = true;
            
    ...