Apple WebObjects 5 Manual de usuario descargar pdf (Pagina 30)

30 Mapping Your Enterprise Objects to Database Tables

 Apple Computer, Inc. January 2002

CHAPTER 3

Enterprise Objects

Figure 3-2 Mapping between an enterprise object class and a single table

In actual practice, the mapping is more flexible than this. For example:

■ You can map an entity to a single table, a subset of a table, or to more than one

table. For instance, you can map a Person entity’s firstName and lastName

attributes to a PERSON table but its streetAddress, city, state and zipCode

attributes to an ADDRESS table.

■ Generally, an attribute is mapped to a single column, but the

column-to-attribute correspondence is similarly flexible. You can map an

attribute to a derived column, such as price * discount or salary * 12.

■ You can map an entity to one or more tables.

In addition to mapping tables to entities and columns to attributes, WebObjects

maps primary and foreign key columns to relationships between objects.

WebObjects defines two types of relationships—to-ones and to-manys—which are

both illustrated in Figure 3-3. The relationship a MovieRole has to its Movie is a

to-one relationship, while the relationship a Movie has to its MovieRoles is a

to-many.

Talent

lastName "Farina"

firstName "Dennis"

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Apple WebObjects 5 Manual de usuario Pagina 30