Understanding TopLink Mapping Concepts

With TopLink mappings, you persist objects by storing (i.e., mapping) information about them in a relational database. There are three components to a mapping:

The object being mapped
The descriptor, or object-to-database table translator
The database table or tables in which you stored the object

Although TopLink supports more complex mappings, most TopLink classes map to a single database table that defines the type of information available in the class. Each object instantiated from a given class maps to a single row comprising the object's attributes, plus an identifier (the primary key) that uniquely identifies the object.

Figure 5-1 How Classes and Objects Map to a Database Table

This illustration shows a simplified view of mapping, and illustrates how objects map to database tables.

Figure 5-1 illustrates the simplest case in which:

Table_X in the database represents Class_X.
Object_X₁ and Object_X₂ are instances of Class_X.
Individual rows in Table_X represent Object_X₁and Object_X₂, as well as any other instances of Class_X.

In addition to this simple example, TopLink allows you create complex mappings, such as transforming a class or object into database table or row.