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Thus the queries on the object view components_or_view give results similar to our equivalent object table, components_nt. The following is another select statement from the object view as an illustration. Notice that we no longer need to use the nested_table_get_refs hint here, as there is no nested table in our object view! If we do supply the hint, it will be ignored. benchmark@ORA10G> select p.* 2 from components_or_view c, TABLE (c.parts) p; COMPONENT_ID PART_ID PART_NAME PART_DESC ------------ ------- ---------- -------------------1 1 part11 part 11 desc 1 2 part12 part 12 desc 2 3 part21 part 21 desc 2 4 part22 part 22 desc If our inserts, updates, and deletes are done directly on the underlying tables components_rel and parts_rel (not on the view components_or_view), then we are done as far as the object view solution goes. But what if we wanted to carry out inserts, updates, and deletes directly on the object view (instead of on the relational tables on which it is based) In such situations, we need to define instead of triggers on the object view.

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We ll take a look at the earliest point you can do some preprocessing on the values that may be stored in here..

o far in this book you ve seen functions and objects that process their inputs immediately using a single thread of execution where the code runs to completion and produces useful results or state changes. In this chapter, you ll turn your attention to concurrent, parallel, asynchronous, and reactive programs. These each represent substantially different approaches to programming from those you ve seen so far. Some of the reasons for turning to these techniques are as follows: To achieve better responsiveness in a graphical user interface (GUI) To report progress results during a long-running computation and to support cancellation of these computations To achieve greater throughput in a reactive application or service To achieve faster processing rates on a multiprocessor machine or cluster To take advantage of the I/O parallelism available in modern disk drives or network connections To sustain processing while network and disk I/O operations are in process In this chapter, we cover some of the techniques that can help achieve these outcomes: Using .NET threads and the BackgroundWorker class for background computations Using events and messages to report results back to a GUI Using F# asynchronous workflows and the .NET thread pool to handle network requests and other asynchronous I/O operations Using F# pattern matching to process message queues Using low-level .NET shared-memory primitives to implement new concurrency techniques and control access to mutable data structures

Note instead of triggers provide a transparent way of performing DMLs on views. These triggers are called instead of triggers because, unlike other types of triggers, Oracle fires the trigger instead of executing the triggering statement. For more information on this and other types of triggers, see the section Types of Triggers in 22 of Oracle Database Concepts (10g Release 1).

In this section, we ll explore the various instead of triggers required to perform inserts, updates, and deletes. Our approach is to perform a particular DML on the object view without the trigger and note its failure. Then we ll define a trigger that will make the DML succeed. The code presented in this section is adapted largely from the code in the section The O-R View of 20 of the book Expert One-on-One Oracle (Apress, ISBN: 1-59059-243-3) written by Tom Kyte. We begin with defining instead of triggers that enable updates on the object view.

In 11 we looked at the most common type of reactive program: GUI programs that respond to events raised on the GUI thread. The inner loop of such an application (contained

Here, user A s changes overwrite the changes made by user B. This is the easiest solution to implement, as it requires that you do nothing other than squash the changes made by user B without telling either user about it. This is not acceptable under most circumstances. Users quite frequently confuse this architectural solution with something entirely different that they call a bug.

As mentioned earlier, our approach is to demonstrate the need for a trigger by first running an operation that fails, and then writing a trigger to make the operation succeed.