Working with Type Conversion Mappings

Type conversion mappings explicitly map a database type to a Java type. For example, a Number in the database can be mapped to a String in Java, or a java.util.Date in Java can be mapped to a java.sql.Date in the database.

For Oracle9 databases, OracleAS TopLink supports NCHAR, NAVRCHAR2, and NCLOB database types. Use the Ncharacter, NString, and NClob target types, respectively.

Example 5-2 Type Conversion Mapping Example

Figure 5-3 illustrates a type conversion mapping. Because the java.util.Date class is stored by default as a Timestamp in the database, it must first be converted to an explicit database type such as java.sql.Date (required only for DB2— most other databases have a single date data-type that can store any date or time).

Figure 5-3 Type Conversion Mappings

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Creating Type Conversion Mappings

Use this procedure to create a type conversion mapping.

To create a type conversion mapping:

Select the attribute to be mapped from the Navigator pane.
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Click the Type Conversion Mapping button on the mapping toolbar.
From the Database field and Database type drop-down lists on the General tab in the Editor pane, choose the appropriate database field and database type.

Figure 5-4 Type Conversion Mapping Properties

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You can also specify:

Read-only attributes – See "Specifying Read-Only Settings" on page 4-72
Access methods – See "Specifying Direct Access and Method Access" on page 4-71