Type Mapping 
It is possible to map a persistent field to a database column when the Java type of the field is compatible with the JDBC type of the column. This ensures that no data is lost when reading a persistent field on all supported platforms.
The following table lists the compatible JDBC types for the basic Java types. For each Java type there is a default JDBC mapping, which should be used whenever possible.
Java and JDBC Type Mapping
|
Java Type |
Acceptable JDBC Type |
Default JDBC Type |
|
boolean, java.lang.Boolean |
SMALLINT, BIT, INTEGER, BIGINT |
SMALLINT |
|
byte, java.lang.Byte |
SMALLINT, DECIMAL, NUMERIC |
SMALLINT |
|
short, java.lang.Short |
SMALLINT, DECIMAL, NUMERIC |
SMALLINT |
|
int, java.lang.Integer |
INTEGER, DECIMAL, NUMERIC |
INTEGER |
|
long, java.lang.Long |
BIGINT, DECIMAL, NUMERIC |
BIGINT |
|
float, java.lang.Float |
REAL, FLOAT, DOUBLE |
REAL |
|
double, java.lang.Double |
DOUBLE |
DOUBLE |
|
char, java.lang.Character |
INTEGER, CHAR , DECIMAL, NUMERIC |
INTEGER |
|
java.lang.String |
VARCHAR, LONGVARCHAR, CLOB, CHAR |
VARCHAR, LONGVARCHAR, CLOB
The default JDBC type for java.lang.String depends on the maximum length of string to be stored. For a maximum length of 127, the default is VARCHAR. For a maximum length of 1333, the default is LONGVARCHAR. If the maximum length is bigger than 1333, the default is CLOB. |
|
java.util.Date |
TIMESTAMP, BIGINT |
TIMESTAMP |
|
java.sql.Date |
DATE |
DATE |
|
java.sql.Time |
TIME |
TIME |
|
java.sql.Timestamp |
TIMESTAMP |
TIMESTAMP |
|
java.lang.Local |
VARCHAR, CHAR, LONGVARCHAR |
VARCHAR |
|
java.lang.BigInteger |
DECIMAL, NUMERIC |
DECIMAL |
|
java.lang.BigDecimal |
DECIMAL, NUMERIC |
DECIMAL |
The following table contains the permitted JDBC types for columns with special function – for example, the discriminator column.
JDBC Types for Columns with Special Function
|
Column |
Acceptable JDBC Type |
Default JDBC Type |
|
Discriminator |
VARCHAR, CHAR, LONGVARCHAR |
VARCHAR |
|
Count |
INTEGER |
INTEGER |
|
Reference |
VARCHAR, CHAR, LONGVARCHAR, VARBINARY, LONGVARBINARY |
VARCHAR |
|
Serialized Data |
BLOB |
BLOB |