web server - Borland Technical Publications

Setting Properties
Automatic table mapping
The Borland EJB container has the capability to automatically map Java types defined
in the enterprise bean code to database table types. However, while it may create
these tables automatically, it does not necessarily use the most optimal mapping
approach. In fact, automatically generating these mappings and tables is more of a
convenience for developers.
The Borland-generated tables are not optimized for performance. Often, they overuse
database resources. For example, the container maps a Java String field to the
corresponding SQL VARCHAR type. However, the mapping is not sensitive to the actual
length of the Java field, and so it maps all string fields to the maximum VARCHAR length.
Thus, it might map a two-character Java String to a VARCHAR(2000) column.
In a production situation, it is preferable for database administrators (DBA) to create
the tables and do the type mapping. The DBA can override the default mappings and
produce a table optimized for performance and use of database resources.
While all relational databases implement SQL types, there may be significant variations
in how they implement these types. Even when they support SQL types with the same
semantics, they may use different names to identify these types. For example, Oracle
implements a Java boolean as aNUMBER(1,0), while Sybase implements it as a BIT and
DB2 implements it as a SMALLINT.
When the Borland EJB Container creates the database tables for your enterprise
beans, it automatically maps entity bean fields and database table columns. The
container must know how to properly specify the SQL types so that it can correctly
create the tables in each supported database. As a result, the EJB Container maps
some Java types differently, depending on the database in use. The following table
shows the mapping for Oracle, Sybase/MSSQL, and DB2:
Java types Oracle Sybase/MSSQL DB2
boolean/Boolean NUMBER(1,0) BITSMALLINT
byte/Byte NUMBER(3,0) TINYINT SMALLINT
char/Character CHAR(1) CHAR(1) CHAR(1)
double/Double NUMBER FLOATFLOAT
float/Float NUMBER REAL REAL
int/Integer NUMBER(10,0) INTINTEGER
long/Long NUMBER(19,0) NUMERIC(19,0) BIGINT
short/Short NUMBER(5,0) SMALLINTSMALLINT
String VARCHAR(2000) TEXT VARCHAR(2000)
java.math.BigDecimal NUMBER(38) DECIMAL(28,28) DECIMAL
byte[] LONG RAW IMAGE BLOB
java.sql.Date DATE DATETIME DATE
java.sql.Time DATE DATETIME TIME
java.sql.Timestamp DATE DATETIME TIMESTAMP
java.util.Date DATE DATETIME TIMESTAMP
java.io.Serializable RAW(2000) IMAGE BLOB
124 BES Developer’s Guide