Java Schema Definition

Java applications define the database classes to be managed in the eXtremeDB runtime using native Java class syntax applying special annotations.

For example, the following code snippet would define a database with two classes Department and Employee:

 
    @Persistent()
    class Department
    {
        @Indexable(Type = Database.IndexType.BTree, Unique = true)
        public String code;
        public String name;
        @Indexable(Type = Database.IndexType.Hashtable, Unique = true)
        public int dept_no;
    }
     
    @Index("byDept_EmployeeName", Keys = new string[] { "dept_no", "name" }, Unique = false)
     
    @Persistent()
    class Employee
    {
        @Indexable(Type = Database.IndexType.BTree, Unique = true)
        public String  name;
        public int  dept_no;
    }
     

Note that the annotations @Persistent(), @Indexable()and @Index() are used to specify the classes and indexes to be generated and maintained in the database.

eXtremeDB JNI Database Annotations

The annotations that are recognized as eXtremeDB database specifications are as follows:

• Persistent
  
  Class annotation: Marks this class as “stored in the database” and optionally provides some attributes of this class;
  

  Persistent(autoid=true)	Creates an autoid index
  Persistent(list=true)	Creates a list index
  Persistent(large=true)	Declares the standard storage model (default)
  Persistent(compact=true)	Declares the compact storage model
  Persistent(inmemory=true)	Declares this class as in-memory (default)
  Persistent(disk=true)	Declares this class as disk-based (i.e on persistent storage media)
  Persistent(local=true)	Declares this class as local for eXtremeDB High Availability partial replication

• Index
  Class annotation: Defines a compound (multi-field) index; possible properties are:
  

  name="indexName"	Identifies this index
  keys={Key(“field1”) [, Key(“field2”) …] }	List of key fields
  unique=true	Creates a b-tree index (the default), true enforces uniqueness; if false allows duplicates
  thick=true	Optimized for a large number of duplicates
  descending=true	Indexes are ascending by default
  initSize=N	For hash indexes; N is the initial size of the hash table
  type=Database.IndexType.BTree	Possible Database.IndexType values are: BTree - Creates a tree index (the default) Hashtable - Creates a hash index Patricia - Creates a patricia index RTree - Creates an rtree index RTreeOfPoint - Creates an rtree index KDTree - Creates a kdtree index Trigram - Creates a trigram index

  for example:

      @Index(name="byName", keys={ Key("lastName"), Key("firstName") }, unique=true )
  
      class Employee
      {
          String  firstName;
          String  lastName;
          Address address;
          long    salary;
      }
  

• Indexable
  Field annotation: Specifies an index on the following field. The index will have the same name as the field. With the exception of name and keys properties, the possible properties are the same as for class attribute Index (above).
  for example:
  

      class Obj
      {
          @Indexable(Type=Database.IndexType.BTree, Unique=true)
          public int value;
      }
      

• Encoding
  Field annotation: Specifies the encoding of string fields. Can be any valid encoding supported by the Java runtime. UTF-8 is the default. Examples:
  

      @Encoding("UTF-16")
      String s1;
      @Encoding("ASCII")
      String s2;
  

• Blob
  Field annotation: Uses eXtremeDB BLOB type for storing a byte array; for example:
  

      @Blob
      byte photo[];
  

• Dimension
  Field annotation: Specifies the dimension for fixed size arrays (char, scalar) An array without a dimension will be treated as a vector (dynamic array).
  Example:
  

      @Dimension(8)
      String prefix;
  

• Numeric
  Field annotation: Specifies the width and precision for decimal fields.
  Example:
  

      @Numeric(12,3)
  
      decimal d;
      // Equivalent to decimal<12,3> d;
  
  

• Binary
  Field annotation: Specifies a fixed length Binary field.
  Example:
  

      @Binary(100)
  
      byte[] dim100_binary;
      // A Binary array of 100 bytes
  
  

• Varbinary
  Field annotation: Specifies a variable length Binary field.
  Example:
  

      @Varbinary
  
      byte[] var_binary;
      // A Binary vector (dynamic array)
  

• Nullable
  Field annotation: Specifies that this field can be null.
  Example:
  

      @Nullable
  
      bool isALive; // Explicitly declared nullable field
  

• OptionalStruct
  Field annotation: Defines a structure field as optional; for example:
  

      @OptionalStruct
      NestedStruct opt_nested; // optional NestedStruct opt_nested;
  

• References
  Field annotation: Used to declare a field of type ref which refers to a Class in the schema; for example:
  

      @References(ClassA.class)]
      long a;
  

• Sequence
  Field annotation: Used to declare a field of type sequence; for example:
  

      @Sequence(type=Sequence.Type.UInt8)
      OrderedSequence stamp;
  

  Note that when an OrderedSequence is declared the default order is Ascending. The default can be overwritten explicitly:
  

      @Sequence(order=Sequence.Order.Descending, type=Sequence.Type.UInt8)
      OrderedSequence stamp;