About Oracle ADF Entity Objects

Oracle ADF entity objects are business components that encapsulate the business model, including data, rules, and persistence behavior, for items that are used in your application. For example, entity objects can represent:

Elements of the logical structure of the business, such as product lines, departments, sales, and regions
Business documents, such as invoices, change orders, and service requests
Physical items, such as warehouses, employees, and equipment

To define an entity object, see Creating an Entity Object Definition.

Entity Objects and Datasources

Entity objects map to single objects in the datasource. In the vast majority of cases, these are tables, views, synonyms, or snapshots in a database. Advanced programmers can base entity objects on objects from other datasources, such as spreadsheets, XML files, or flat text files.

When entity objects are based on database objects, columns in the database object map to single entity object attribute in the entity object. The definitions of these attributes (reflected in the entity object's XML file, as described below) reflect the properties of these columns, including data types, column constraints, and precision and scale specifications. When entity objects are based on objects from other datasources, entity object attributes map to "columns" from those objects, as defined by the programmer. For more information about entity object attributes, see the related topics list.

Entity objects handle the posting of changes to the datasource.

Because entity objects are business domain components, you do not need to develop entity objects around your application's data needs. They should instead be the most logical representation of your data. If your datasource is well-designed, their structure can be isomorphic to that of the datasource.

JDeveloper will help you both engineer entity objects from existing database tables and generate database tables from entity objects.

Entity Objects and Business Rules

Entity objects provide a hook for implementing your application's business rules, including:

Validation logic, which keeps corrupt data from being entered in the database
Security logic, which tracks data changes and ensures that only authorized users can see or change data
Creation logic, which performs actions (such as prepopulating attributes) for newly created rows
Deletion logic, which performs actions when rows are deleted
Other logic, such as dynamic calculations and events that trigger when data is modified

Many simple business rules can be implemented declaratively and are stored in the entity object's XML file. More complex business rules require extending framework base classes.

Entity Object Definitions, Entity Object Usages, Entity Object Instances

Often, it is important to distinguish between the following:

Entity object definitions, which consist of the XML file and any extended Java classes (see below) for the entity object
Entity object usages, which are particular references to a Oracle ADF entity object definition within a Oracle ADF view object definition
Entity object instances, which are single instances of the entity object class (see below), representing a single row

You create entity object definitions using JDeveloper's tools. Usages of that definition can then be added to view object definitions. Entity object instances are used solely at runtime. For more information, see the related topics list.

Entity Objects, XML Files, and Java Classes

Like most business components, individual entity objects are partially defined by XML files. These files specify:

Simple metadata about the datasource, such as the table name and attribute definitions
Simple business logic, such as the business logic that represents most column constraints and simple validation and security logic

If an XML file satisfies your needs for a particular entity object, you may not need to extend any classes or write any Java code

In addition to XML files, entity object definitions comprise up to three Java classes:

The entity object class - an instance of this class (an entity object instance) represents a single row from the datasource
The entity collection class - an instance of this class represents the collection of rows currently in memory for a single user
The entity definition class - the singleton instance of this class represents represents the entire datasource object

For more information, see the related topics list.