Understanding the Schema Manager

Figure 6-1 summarizes the important SchemaManager classes and the primary means of using them.

Figure 6-1 SchemaManager Usage

Description of "Figure 6-1 SchemaManager Usage"

Although you can use the SchemaManager API directly, Oracle recommends that you create a TableCreator class and use its API (which, in turn, uses the SchemaManager).

You can automatically generate a TableCreator using:

• TopLink Workbench during development (see "Using TopLink Workbench During Development")

• DefaultTableGenerator at run time (see "Using the Default Table Generator at Run Time")

The TableCreator class owns one or more TableDefinition classes (one for each database table) and the TableDefinition class owns one or more FieldDefinition classes (one for each field).

The TableDefinition class lets you specify a database table schema in a generic format. At run time, TopLink uses the session associated with your TopLink project to determine the specific database type, and uses the generic schema to create the appropriate tables and fields for that database.

After creating a TableCreator class, you can use its API to create and drop tables (see "Creating Tables With a Table Creator"). You can also configure TopLink to do this automatically (see "Automatic Database Table Creation").

Because the schema manager uses Java types rather than database types, it is database-independent. However, because it does not account for database-specific optimizations, it is best-suited for development purposes rather than production. For more information on how the schema manager maps Java types to database types, see "Schema Manager Java and Database Type Conversion".

Although the schema manager can handle the sequencing configuration that you specify in your TopLink project, if you are using sequencing with non-Oracle databases, there are some sequencing restrictions you should be aware of (see "Sequencing").

Schema Manager Java and Database Type Conversion

Table 6-1 lists the Java type to database type conversions that the schema manager supports depending on the database platform your TopLink project uses. This list is specific to the schema manager and does not apply to mappings. TopLink automatically performs conversions between any database types within mappings.

Table 6-1 Java and Database Field Type Conversion

Java Type	Database Type
	Oracle	DB2	Sybase	MySQL	MS Access
java.lang.Boolean	NUMBER	SMALLINT	BIT default 0	TINYINT(1)	SHORT
java.lang.Byte	NUMBER	SMALLINT	SMALLINT	TINYINT	SHORT
java.lang.Byte[]	LONG RAW	BLOB	IMAGE	BLOB	LONGBINARY
java.lang.Character	CHAR	CHAR	CHAR	CHAR	TEXT
java.lang.Character[]	LONG	CLOB	TEXT	TEXT	LONGTEXT
java.lang.Double	NUMBER	FLOAT	FLOAT(32)	DOUBLE	DOUBLE
java.lang.Float	NUMBER	FLOAT	FLOAT(16)	FLOAT	DOUBLE
java.lang.Integer	NUMBER	INTEGER	INTEGER	INTEGER	LONG
java.lang.Long	NUMBER	INTEGER	NUMERIC	BIGINT	DOUBLE
java.lang.Short	NUMBER	SMALLINT	SMALLINT	SMALLINT	SHORT
java.lang.String	VARCHAR2	VARCHAR	VARCHAR	VARCHAR	TEXT
java.math.BigDecimal	NUMBER	DECIMAL	NUMERIC	DECIMAL	DOUBLE
java.math.BigInteger	NUMBER	DECIMAL	NUMERIC	BIGINT	DOUBLE
java.sql.Date	DATE	DATE	DATETIME	DATE	DATETIME
java.sql.Time	DATE	TIME	DATETIME	TIME	DATETIME
java.sql.Timestamp	DATE	TIMESTAMP	DATETIME	DATETIME	DATETIME

For more information about database platforms that TopLink supports, see "Database Platforms".

Sequencing

If you generate a TableCreator class using TopLink Workbench (see "Using TopLink Workbench During Development") or DefaultTableGenerator (see "Using the Default Table Generator at Run Time"), then sequencing configuration is included in your TableCreator according to your TopLink project configuration. In this case, when you use TableCreator method createTables, it does the following:

• 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

You can use advanced API to handle special cases like Sybase or Microsoft SQL Server native sequencing (see "Using Java").

For more information about sequencing, see "Understanding Sequencing in Relational Projects".