Schema Manager

Creating a Table Definition

The TableDefinition class includes all the information required to create a new table, including the names and properties of a table and all its fields.

The TableDefinition class has the following methods

setName()
addField()
addPrimaryKeyField()
addIdentityField()
addForeignKeyConstraint()

All table definitions must call the setName() method to set the name of the table that is described by the TableDefinition.

Adding Fields to a Table Definition

Use the addField() method to add fields to the TableDefinition. To add the primary key field to the table, use the addPrimaryKeyField() method rather than the addField() method.

To maintain compatibility among different databases, the type parameter requires a Java class rather than a database field type. OracleAS TopLink translates the Java class to the appropriate database field type at runtime. For example, the String class translates to the CHAR type for dBase databases. However, if you are connecting to Sybase, the String class translates to VARCHAR.

The addField() method can also be called with the fieldSize or fieldSubSize parameters for column types that require size and subsize to be specified.

Some databases require a subsize, but others do not. OracleAS TopLink automatically provides the required information, as necessary.

Defining Sybase and Microsoft SQL Server Native Sequencing

The addIdentityField() methods have the following definitions:

addIdentityField(String fieldName, Class type) 
addIdentityField(String fieldName, Class type, int fieldSize)

These methods enable you to add fields representing a generated sequence number from Sybase or Microsoft SQL Server native sequencing.

The OracleAS TopLink Two-Tier Example illustrates the table creation mechanism in the EmployeeTableCreator.java file located in the <ORACLE_HOME>\toplink\examples\foundation\twotier\src\examples\sessions\twotier\ directory.

Creating Tables on the Database

OracleAS TopLink offers two methods that enable you to pass the initialized TableDefinition object to the DatabaseSession Schema Manager:

• The createObject() method creates a new table in the database, according to the table definition.

  SchemaManager schemaManager = new SchemaManager(session);
  schemaManager.createObject(Tables.employeeTable());
  
  

• The replaceObject() method destroys and re-creates the schema entity in the database.

  SchemaManager schemaManager = new SchemaManager(session);
  schemaManager.replaceObject(Tables.addressTable());
  
  

Creating the Sequence Table

If your application requires a sequence table, invoke the createSequences() method on the Schema Manager:

SchemaManager schemaManager = new SchemaManager(session);
schemaManager.createSequences();

The preceding code:

• Creates the sequence table as defined in the session DatabaseLogin

• Creates or inserts sequences for each sequence name for all registered descriptors in the session

• Creates the Oracle sequence object if you use Oracle native sequencing