Apple WebObjects 5 Manuel d'utilisateur télécharger pdf (Page 32)

32 WebObjects Support for Enterprise-Object Instances

 Apple Computer, Inc. January 2002

CHAPTER 3

Enterprise Objects

in-memory enterprise-object instances. WebObjects has mechanisms for ensuring

the integrity of your data is maintained between your application and the

datasource without sacrificing performance or flexibility:

Validation

A good part of your application’s business logic is usually validation

(for example, verifying that customers don’t exceed their credit limits,

return dates don’t come before their corresponding check-out dates, and

so on). In your enterprise-object classes, you implement methods that

check for invalid data, and WebObjects automatically invokes them

before saving anything to the datasource.

Referential-integrity enforcement

In your model you can specify rules governing the relationships

between entities, such as whether a to-one relationship is optional or

mandatory. You can also specify delete rules—actions that must occur

when an enterprise-object instance is deleted. For example, if you have

a Department entity, you can specify that when instances of it are

deleted, all the related employees in that department are also deleted (a

cascading delete), all the employees in that department are updated to

have no department (nullify), or the department deletion is rejected if it

has any employees (deny).

Automatic primary and foreign key generation

You do not need to maintain database artifacts such as primary and

foreign key values in your application; WebObjects keeps track of them

for you. Primary and foreign keys aren’t usually meaningful parts of a

business model; rather, they’re attributes created in a relational

database to express relationships between entities. Key values can be

generated and propagated automatically.

Transaction management

Most transactions are handled for you, using the native transaction

management features of your database to group database operations

that correspond to the changes that have been made to enterprise-object

instances in memory. You don’t have to worry about beginning,

committing, or rolling back transactions unless you want to fine-tune

transaction-management behavior. WebObjects also provides a separate

in-memory transaction management feature that allows you to create

nested contexts in which a child context’s changes are folded into the

parent context only upon successful completion of an in-memory

operation.

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