3
Design Time and Runtime Concepts

This chapter describes the design time and runtime concepts for the Database adapter. Topics include:

Database Adapter Design Time Concepts

The following topics discuss the iStudio concepts pertinent to the Database adapter.

Oracle9iAS InterConnect User Guide

Importing Database Tables

For a database application, the application and common views resemble the underlying database schema. For this reason, iStudio allows the creation of a view by importing tables directly from the database. The following tables can be imported:

Relational
Object
Oracle Object
Advanced Queuing payload.

The following examples illustrate some basic features for the database tables.

Example: Relational Table

The following example illustrates basic features of a relational table.

Table 3-1 Customer

Parameter	Value
`NAME`	`VARCHAR2(200)`
`ID`	`NUMBER`
`ADDRESSES`	`LONG`

When imported into iStudio, this table results in the following:

Table 3-2 Customer

Parameter	Value
`NAME`	`STRING`
`ID`	`INTEGER`
`ADDRESSES`	`STRING`

When importing from database, iStudio allows any number of columns to be selected.

Example: Object Table

The following example illustrates basic features of the object table.

Table 3-3 Customer

Parameter	Value
`NAME`	`VARCHAR2(200)`
`ID`	`NUMBER`
`ADDRESSES`	`ADDRESS_ARRAY`

Where ADDRESS_ARRAY is VARRAY of ADDRESS and ADDRESS is an OBJECT TYPE containing the following attributes:

Parameter	Value
`CITY`	`VARCHAR2(200)`
`STATE`	`VARCHAR2(200)`
`ZIP`	`NUMBER`

When imported into iStudio, this table results in the following:

Table 3-4 Customer

Parameter	Value
`NAME`	`STRING`
`ID`	`INTEGER`
`ADDRESSES`	`ARRAY` (marked as an `ARRAY`)

Where ADDRESS_ARRAY contains the following attributes:

Parameter	Value
`CITY`	`STRING`
`STATE`	`STRING`
`ZIP`	`NUMBER`

In this example, the hierarchical structure is kept intact when dealing with Oracle Object Types.

Example: FOREIGN Key

In an example similar to the previous one, the structure or relationship is represented using a FOREIGN key. In this case, the end user is responsible for importing each of the different tables and setting up the relationship in iStudio by editing the types of attributes. The following example illustrates this point.

Relational Tables related by a FOREIGN Key

Table 3-5 Customer

Parameter	Value
`NAME`	`VARCHAR2(200)`
`ID`	`NUMBER`
`ADDRESS`	`NUMBER` (Foreign key)

Table 3-6 Address

Parameter	Value
`ID`	`NUMBER` (Primary key)
`CITY`	`VARCHAR2(100)`
`STATE`	`VARCHAR2(50)`
`ZIP`	`NUMBER`

Using iStudio, complete the following to import this structure:

Import the Address table.

This results in:

STATE

STRING

ZIP

NUMBER
Import the Customer table. This results in the following:

ID

NUMBER

ADDRESS

NUMBER
Change the type of Address attribute to Address.

Importing an Oracle Object or Advanced Queuing Payload

Importing an Oracle Object or an Advanced Queuing payload in iStudio is similar to importing database tables. Importing from an Advanced Queuing payload is necessary when working with Advanced Queuing applications.

Note:

When importing an Advanced Queuing payload, it may be necessary to log in as the system user.

Returned In Arguments

Returned In arguments applies when invoking procedures. The Returned IN Args page does only displays in the Invoke wizard. Returned In arguments are used to propagate INOUT attributes contained in the request to the reply. Without this feature, it would have to be ensured that these attributes exist in both the common view and application view of the implementor and are INOUT attributes. It would also be necessary to complete all the mappings to copy these attributes on their way out and back in, for example, when receiving the reply. For instance, one of these returned In arguments can be used to correlate the reply with an asynchronous request.

For example, a Customer object looks like the following in the application view:

Customer
  Name
  ID
  Contact
    Address
      City
      State
      Zip
    Phone
      AreaCode
      PhoneNumber

If this is to be sent as part of a CreateCustomer message and ID is to be INOUT in both the request and the reply, then it should be an INOUT parameter. To do this, complete the following steps:

Click Returned In Args on the Invoke wizard.
Select ID on the Please Select In Arguments dialog and the Please Select Out Arguments dialog.

Exporting PL/SQL Code

To export PL/SQL code, use the File/Export menu item in iStudio.

The SQL Code dialog appears at the end of Subscribe, Invoke, Implement wizards. In the drop down list the options are generated data types and <EventType>_<EventName>_<MetadataOwner>_<Version>.

Typically, there is no need to modify the generated data types SQL code. Insert the necessary code as indicated by -- declare here or -- fill code here in the latter dialog.

Database Adapter Runtime Concepts

The following section describes the runtime concepts pertinent to the Database Adapter.

How the Database Adapter Works

The following topics describe how the Database adapter works.

Sending Adapter

The Database adapter is comprised of the database bridge and the runtime agent. The bridge is constantly polling the MESSAGEOBJECTTABLE table in the oai schema, specified by the db_bridge_schema1_username parameter. A new row in this table indicates a new outbound Oracle9iAS InterConnect message waiting to be sent by this adapter. The adapter then picks up the message from the interface tables residing in the oai schema, builds the corresponding Oracle9iAS InterConnect message, persists it, transforms it to the common view, and routes it to the hub. From the hub, the message gets routed to the appropriate subscriber based on configuration completed in iStudio which can be content-based or subscription-based.

The application and the database adapter communicate through the interface tables residing in the oai schema for outbound messages and through iStudio PL/SQL generated procedures for inbound messages. Therefore, if the adapter is down while the application is publishing Oracle9iAS InterConnect messages using the iStudio generated PL/SQL procedures, the messages are held in the interface tables and will be picked up in a FIFO method by the database adapter once it is up and running. If there are messages in the interface tables that no longer need to be published, the DELETE FROM MESSAGEOBJECTTABLE using SQLPlus can be run in the oai schema.

Receiving Adapter

On the subscribing/receiving side, the Database adapter receives the message from the hub, transforms it from common view to application view, and passes it to the bridge which calls the appropriate PL/SQL procedures to inform the application about the newly arrived message. If this adapter were an implementor, the OUT arguments from the PL/SQL procedure invocation are put together and the REPLY in the form of another Oracle9iAS InterConnect message is sent back to the INVOKER or REQUESTER.

The receiving adapter is responsible for creating any necessary cross reference entries. In a publish-subscribe scenario, the subscribing adapter creates the cross reference entry using the returned arguments, for example OUT, from the subscribe side procedure.

See Also: