Conversion of CMP Types to Database Types

In defining the container-managed persistent fields in the <cmp-field> and the primary key types, you can define simple data types and Java user classes that are serializable.

• Simple Data Types

• Serializable Classes

• Other Entity Beans or Collections

Simple Data Types

The following table provides a list of the supported simple data types, which you can provide in the persistence-type attribute, with the mapping of these types to SQL types and to Oracle database types. None of these mappings are guaranteed to work on non-Oracle databases.

Table 5-1 Simple Data Types

Known Type (native)	SQL type	Oracle type
java.lang.String	VARCHAR(255)	VARCHAR2(255)
java.lang.Integer[ ]	INTEGER	NUMBER(20,0)
java.lang.Long[ ]	INTEGER	NUMBER(20,0)
java.lang.Short[ ]	INTEGER	NUMBER(10,0)
java.lang.Double[ ]	DOUBLE PRECISION	NUMBER(30,0)
java.lang.Float[ ]	FLOAT	NUMBER(20,5)
java.lang.Byte[ ]	SMALLINT	NUMBER(10,0)
java.lang.Character[ ]	CHAR	CHAR(1)
java.lang.Boolean[ ]	BIT	NUMBER(1,0)
java.util.Date	DATETIME	DATE
java.sql.Date	DATE	DATE
java.util.Time	DATE	DATE
java.sql.Timestamp	TIMESTAMP	TIMESTAMP
java.lang.String	CLOB	CLOB
char[ ]	CLOB	CLOB
byte[ ]	BLOB	BLOB
java.io.Serializable (4KB limit)	LONGVARBINARY	BLOB

Note: You can modify the mapping of these data types in the config/database-schema/<db>.xml XML configuration files.

The Date and Time map to DATE in the database, because the DATE contains the time. The Timestamp, however, maps to TIMESTAMP in the database, which gives the time in nanoseconds.

Mapping java.sql.CLOB and java.sql.BLOB directly is not currently supported because these objects are not serializable. However you can map a String or char[] and byte[] to database column type CLOB and BLOB respectively. Mapping a char[] to a CLOB or a byte[] to a BLOB can only be done with an Oracle database. The Oracle JDBC API was modified to handle this operation.

There is a 4 KB limit when mapping a serialized object to a BLOB type over the JDBC Thin driver.

When String and char[] variables map to a VARCHAR2 in the database, it can only hold up to 2K. However, you can map String object or char[] larger than 2K to a CLOB by doing the following:

1. The bean implementation uses the String or char[] objects.

2. The persistence-type attribute of the <cmp-field-mapping> element defines the object as a CLOB, as follows:

	<cmp-field-mapping name="stringdata" persistence-name="stringdata"              persistence-type="CLOB" />

In the same manner, you can map a byte[] in the bean implementation to a BLOB, as follows:

	<cmp-field-mapping name="bytedata" persistence-name="bytedata"              persistence-type="BLOB" />

Serializable Classes

In addition to simple data types, you can define user classes that implement Serializable. These classes are stored in a BLOB in the database.

Other Entity Beans or Collections

You should not define other entity beans or Collections as a CMP type. Instead, these are relationships and should be defined within a CMR field.

• A relationship to another entity bean is always defined in a <cmr-field> relationship.

• Collections promote a "many" relationship and should be configured within a <cmr-field> relationship. Other types, such as Lists, are sub-interfaces of Collections. Oracle recommends that you use Collections.