Working with Direct Mappings

There are two basic ways of storing object attributes directly in a database table:

The information can be stored directly if the attribute type is comparable to a database type.
If there is no database primitive type that is logically comparable to the attribute's type, it must be transformed on its way to and from the database.

In TopLink, direct mappings define how a persistent object refers to objects without descriptors, such as the JDK classes and primitives.

You can create the following direct mappings in TopLink:

Direct-to-field mappings - Map a Java attribute directly to a database field (see "Working with Direct-to-Field Mappings" ).
Type conversion mappings - Map Java values with simple type conversions, such as from character to string (see "Working with Type Conversion Mappings" ).
Object type mappings - Use an association to map values to the database (see "Working with Object Type Mappings" ).
Serialized object mappings - Map serializable objects, such as multimedia objects, to database BLOB fields (see "Working with Serialized Object Mappings" ).
Transformation mappings - Allow you to create custom mappings where one or more fields can be used to create the object be stored in the attribute (see "Working with Transformation Mappings" ).

If the application's objects contain attributes that cannot be represented as direct-to-field, type conversion, or object-type mappings, then the application must provide transformation routines for saving the attributes.

If a direct-to-field mapping cannot be used to perform the desired conversion, try type conversion and object type mappings before attempting to define a custom transformation mapping.