About Oracle ADF View Links

Oracle ADF view links are business components that define a relationship between two Oracle ADF view object definitions (the "source" and "destination" view objects) based on sets of view attributes (the "source" and "destination" attributes) from each. These can range from simple one-to-many relationships to complex many-to-many relationships. This allows you to easily create master/detail relationships between data controls in the client. For example, creating a view link between view objects will allow you to create relationships between:

A dropdown list for selecting a customer and a table displaying that customer's orders
The nodes in a tree control and their respective children
An HTML page containing two frames: one that allows the user to browse for items and the other that lists the wherehouses in which the selected item is stored

Because view objects are data model components, you should consider your client's data needs when defining them. Decide which controls will need to be related, and which view objects will manage them.

To define a view link, see Representing Relationships Between Query Results.

View Link Definitions and View Link Instances

Often, it is important to distinguish between the following:

View link definitions, which consist of an XML file that defines the view link
View link instances, which are particular references to a Oracle ADF view link definition within a Oracle ADF application module definition

You create a view link definition using JDeveloper's tools, based on two view object definitions. Instances of that view link can then be used to relate view object instances in application module definitions. For more information, see the related topics list.

View Links and Queries

A view link definition relates two view object definitions. In the vast majority of cases, the view object definitions will contain SQL queries that access a database, and the view link definition will relate those queries using a parametrized WHERE clause, which is appended to the destination view object's query and resolved using the values of source attributes.

For example, suppose you had the following view object definitions:

CustomersView, containing the query
SELECT * FROM CUSTOMERS
OrdersView, containing the query
SELECT * FROM ORDERS

You could create a view link, CustOrdLink, with

CustomersView's CustomerId attribute as its source attribute
The parametrized WHERE clause
WHERE :1 = ORDERS.CUSTOMER_ID

You could then use CustOrdLink conjunction with a row from CustomersView (for example, the row for Customer 101) and all of OrdersView to return the rows from the query

SELECT * FROM ORDERS
WHERE 101 = ORDERS.CUSTOMER_ID

JDeveloper will create the parametrized query for you based on the attributes you select. If you do not change this query, you can make the view link bidirectional. This will switch the roles of the source and destination attributes. For example, if you make CustOrdLink bidirectional, you can use it in conjunction with a row from OrdersView (for example, a row for an order placed by Customer 101) and all of CustomersView to return the rows from the query

SELECT * FROM CUSTOMERS
WHERE CUSTOMERS.CUSTOMER_ID = 101

View Links and Associations

If two view object definitions each contain at least one entity object usage, and there is an association between the entity object definitions used, you can create a view link definition based on the association.

For example, suppose the following is true about CustomersView and OrdersView:

CustomersView contains a usage of the entity object Customers
OrdersView contains a usage of the entity object Orders
There is an association, CustOrdAssoc, between Customers and Orders

In this case, you can base CustOrdLink on CustOrdAssoc , rather than specifying the source and destination attributes yourself.

This is particularly useful if you want to create a many-to-many view link. For example, suppose you had the following business components:

The entity object Items
The entity object Warehouses
The view object ItemsView, containing a usage of Items
The view object WarehousesView, containing a usage of Warehouses
The many-to-many association ItemWarehouseAssoc between Items and Warehouses

You could create a view link, ItemsWarehouseLink, based on ItemsWarehouseAssoc. This view link would allow you to retrieve all warehouses in which a specific item was stored and (if bidirectional) all items stored by a specific warehouse. For more information, see the related topics list.