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One of the easiest ways to get going with concurrency and parallelism is to use the System. ComponentModel.BackgroundWorker class of the .NET Framework. A BackgroundWorker class runs on its own dedicated operating system thread. These objects can be used in many situations but are especially useful for coarse-grained concurrency and parallelism such as checking the spelling of a document in the background. In this section we show some simple uses of BackgroundWorker and how to build similar objects that use a BackgroundWorker internally. Listing 13-1 shows a simple use of BackgroundWorker that computes the Fibonacci numbers on the worker thread. Listing 13-1. A Simple BackgroundWorker open System.ComponentModel open System.Windows.Forms let worker = new BackgroundWorker() let numIterations = 1000 worker.DoWork.Add(fun args -> let rec computeFibonacci resPrevPrev resPrev i = // Compute the next result let res = resPrevPrev + resPrev // At the end of the computation and write the result into the mutable state if i = numIterations then args.Result <- box res else // Compute the next result computeFibonacci resPrev res (i+1) computeFibonacci 1 1 2) worker.RunWorkerCompleted.Add(fun args -> MessageBox.Show(sprintf "Result = %A" args.Result) |> ignore) // Execute the worker worker.RunWorkerAsync() Table 13-1 shows the primary members of a BackgroundWorker object. The execution sequence of the code in Listing 13-1 is as follows: 1. The main application thread creates and configures a BackgroundWorker object. 2. Once configuration is complete, the main application thread calls the RunWorkerAsync method on the BackgroundWorker object. This causes the DoWork event to be raised on the worker thread.

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update parts_rel rp set ( component_id, part_name, part_desc ) = ( select :new.component_id, part_name, part_desc from TABLE( cast( :new.parts as part_type_tab ) ) np where np.part_id = rp.part_id ) where rp.part_id in ( select part_id from ( select * from TABLE( cast( :old.parts as part_type_tab ) ) minus select * from TABLE( cast( :new.parts as part_type_tab ) ) ) );

cmParametersAdd(pm); pm = new SqlParameter ("@org_state", SqlDbTypeChar, 2); pmSourceVersion = DataRowVersionOriginal; pmSourceColumn = "state"; cmParametersAdd(pm); pm = new SqlParameter ("@org_zip", SqlDbTypeChar, 5); pmSourceVersion = DataRowVersionOriginal; pmSourceColumn = "zip"; cmParametersAdd(pm); pm = new SqlParameter ("@org_contract", SqlDbTypeBit); pmSourceVersion = DataRowVersionOriginal; pmSourceColumn = "contract"; cmParametersAdd(pm); daUpdateCommand = cm; daUpdate(ds); return true; } Notice how you re mapping columns of the DataTable to parameters of the CommandText using the SourceColumn and SourceVersion attributes of the parameter object For the parameters in the "set" portion of the SQL statement, you re pulling the current values from the DataTable For columns in the where clause, you re pulling the original values from the DataTable Realize that "select * from authors" is the SelectCommand of the DataAdapter.

All the integer types listed in Table 3-1 support bitwise manipulations on their underlying representations. Table 3-3 shows the bitwise manipulation operators.

Finally, we insert any records in parts_rel that were newly added to the nested table column parts: 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 insert into parts_rel select component_id, part_id, part_name, part_desc from ( select * from TABLE( cast( :new.parts as part_type_tab ) ) where part_id in ( select part_id from TABLE( cast( :new.parts as part_type_tab ) minus select part_id from TABLE( cast( :old.parts as part_type_tab ) ) ); --dbms_output.put_line( 'inserted ' || sql%rowcount end case; end; /

Bitwise and Bitwise or Bitwise exclusive or Bitwise negation Left shift Right shift (arithmetic if signed)

Trigger created. With the preceding, fairly complex trigger in place, we can proceed to successfully carry out updates on the object view. The following is the update that failed earlier, now shown to be running successfully:

What you re building with this code is the UpdateCommand of the adapter, which you set just before calling the Update method Typically, when using an adapter for retrieving data from the database and later moving it back, you ll do a one-time creation of this adapter and cache it, as it s a lot of work This code will also only work for updates to the DataSet; you ll also want to create and set an insert and delete command (for the InsertCommand and DeleteCommand properties of the adapter, respectively) When the user gets into a dirty read situation using this approach, the error displayed in Figure 10-7 occurs In a full-blown application, this is the exception that would be caught and would kick off the rendering of whatever concurrency resolution interface was required by the business rules.

benchmark@ORA10G> declare 2 l_parts part_type_tab; 3 begin 4 select parts 5 into l_parts 6 from components_or_view 7 where component_id = 1; 8 9 for i in 1 .. l_parts.count 10 loop 11 l_parts(i).part_desc := l_parts(i).part_desc || 'changed'; 12 end loop; 13 14 update components_or_view 15 set parts = l_parts 16 where component_id = 1; 17 end; 18 / PL/SQL procedure successfully completed. We are finished with enabling updates. As you can see, the code is fairly complex. Next, we ll look at how to enable inserts directly on the view.