qr code generator c# Inside Microsoft SQL Server 2008: T-SQL Querying in C#

Encode qrcode in C# Inside Microsoft SQL Server 2008: T-SQL Querying

The structure wasn t strong enough to support itself as it was being built. It doesn t matter that it would have been strong enough by the time it was done; it needed to be strong enough at each step. If you construct and integrate software in the wrong order, it s harder to code, harder to test, and harder to debug. If none of it will work until all of it works, it can seem as though it will never be finished. It too can collapse under its own weight during construction the bug count might seem insurmountable, progress might be invisible, or the complexity might be overwhelming even though the finished product would have worked. Because it s done after a developer has finished developer testing and in conjunction with system testing, integration is sometimes thought of as a testing activity. It s complex enough, however, that it should be viewed as an independent activity. Here are some of the benefits you can expect from careful integration: Easier defect diagnosis Fewer defects Less scaffolding

Place the hub in a central location. You must be able to run a cable from the hub to each computer on your network. It s not always feasible to make a direct connection from each computer or other networked device to the central hub. (Furthermore, the central hub might not have enough ports to connect all devices.) To make additional connections in an Ethernet network, use another hub or switch.

One such situation is when you need to insert or modify large volumes of data and, for practical reasons, you split it into batches, modifying one subset of the data at a time. For example, purging historic data might involve deleting millions of rows of data. Unless the target table is partitioned and you can simply drop a partition, the purging process requires a DELETE statement. Deleting such a large set of rows in a single transaction has several drawbacks. A DELETE statement is fully logged, and it will require enough space in the transaction log to accommodate the whole transaction. During the delete operation, which could take a long time, no part of the log from the oldest open transaction up to the current point can be overwritten. Furthermore, if the transaction breaks in the middle for some reason, all the activity that took place to that point will be rolled back, and this will take a while. Finally, when very many rows are deleted at once, SQL Server might escalate the individual locks held on the deleted rows to an exclusive table lock, preventing both read and write access to the target table until the DELETE is completed.

Caution Setting a workbook to calculate manually can be a dangerous practice, especially in a workbook where revisions are made to data that has already been calculated. Users might not realize that formula results haven t been updated, and thereby might use inaccurate results. If you re going to set a workbook to calculate manually, it s best to do it in workbooks where new data is being entered.

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In the Main method, a Manager object is constructed and passed to PromoteEmployee . This code compiles and executes because Manager is ultimately derived from Object, which is what PromoteEmployee expects . Once inside PromoteEmployee, the CLR confirms that o refers to an object that is either an Employee or a type that is derived from Employee . Because Manager is derived from Employee, the CLR performs the cast and allows PromoteEmployee to continue executing . After PromoteEmployee returns, Main constructs a DateTime object and passes it to PromoteEmployee . Again, DateTime is derived from Object, and the compiler compiles the code that calls PromoteEmployee with no problem . However, inside PromoteEmployee, the CLR checks the cast and detects that o refers to a DateTime object and is therefore not an Employee or any type derived from Employee . At this point, the CLR can t allow the cast and throws a System.InvalidCastException . If the CLR allowed the cast, there would be no type safety, and the results would be unpredictable, including the possibility of application crashes and security breaches caused by the ability of types to easily spoof other types . Type spoofing is the cause of many security breaches and compromises an application s stability and robustness . Type safety is therefore an extremely important part of the CLR . By the way, the proper way to declare the PromoteEmployee method would be to specify an Employee type instead of an Object type as its parameter so that the compiler produces a compile-time error, saving the developer from waiting until a runtime exception occurs to discover a problem . I used Object so that I could demonstrate how the C# compiler and the CLR deal with casting and type-safety .

The idea behind the double-check locking technique is that a call to the GetSingleton method quickly checks the s_value field to see if the object has already been created, and if it has, the method returns a reference to it . The beautiful thing here is that no thread synchronization is required once the object has been constructed; the application will run very fast . On the other hand, if the first thread that calls the GetSingleton method sees that the object hasn t been created, it takes a thread synchronization lock to ensure that only one thread constructs the single object . This means that a performance hit occurs only the first time a thread queries the singleton object . Now, let me explain why this pattern didn t work in Java . The Java Virtual Machine read the value of s_value into a CPU register at the beginning of the GetSingleton method and then just queried the register when evaluating the second if statement, causing the second if statement to always evaluate to true, and multiple threads ended up creating Singleton objects . Of course, this happened only if multiple threads called GetSingleton at the exact same time, which in most applications is very unlikely . This is why it went undetected in Java for so long . In the CLR, calling any lock method is a full memory fence, and any variable writes you have before the fence must complete before the fence and any variable reads after the fence must start after it . For the GetSingleton method, this means that the s_value field must be reread after the call to Monitor.Enter; it cannot be cached in a register across this method call . Inside GetSingleton, you see the call to Interlocked.Exchange . Here s the problem that this is solving . Let s say that what you had inside the second if statement was the following line of code:

QMediaPlayer *player = new QMediaPlayer; player->setMedia(QUrl::fromLocalFile("movie.mp4")); widget = new QVideoWidget(player); mainWindow->setCentralWidget(widget); widget->show(); player->play();

Part I:

Addressing is the practice of maintaining a coherent system of addresses within your network so that all computers can communicate.

SET NOCOUNT ON; USE testdb; GO SET LOCK_TIMEOUT 30000; DECLARE @retry AS INT, @i AS INT, @j AS INT, @maxretries AS INT; SELECT @retry = 1, @i = 0, @maxretries = 3; WHILE @retry = 1 AND @i <= @maxretries BEGIN SET @retry = 0; BEGIN TRY BEGIN TRAN SET @j = (SELECT SUM(col1) FROM dbo.T2); WAITFOR DELAY '00:00:05'; UPDATE dbo.T2 SET col1 += 1; WAITFOR DELAY '00:00:05'; SET @j = (SELECT SUM(col1) FROM dbo.T1); COMMIT TRAN PRINT 'Transaction completed successfully.'; END TRY BEGIN CATCH -- Lock timeout IF ERROR_NUMBER() = 1222 BEGIN PRINT 'Lock timeout detected.'; IF XACT_STATE() <> 0 ROLLBACK; END -- Deadlock / Update conflict ELSE IF ERROR_NUMBER() IN (1205, 3960) BEGIN PRINT CASE ERROR_NUMBER() WHEN 1205 THEN 'Deadlock' WHEN 3960 THEN 'Update conflict' END + ' detected.'; IF XACT_STATE() <> 0 ROLLBACK; SELECT @retry = 1, @i += 1; IF @i <= @maxretries BEGIN PRINT 'Retry #' + CAST(@i AS VARCHAR(10)) + '.'; WAITFOR DELAY '00:00:05'; END END ELSE BEGIN PRINT 'Unhandled error: ' + CAST(ERROR_NUMBER() AS VARCHAR(10)) + ', ' + ERROR_MESSAGE(); IF XACT_STATE() <> 0 ROLLBACK; END END CATCH END IF @i > @maxretries PRINT 'Failed ' + CAST(@maxretries AS VARCHAR(10)) + ' retries.';

tempfile is in the standard library, so comes with Ruby by default. To use it, you only need to place this line near the start of your program: require 'tempfile'

Run the webpage. Before entering any information into the TextBox controls, click Register. Verify that the RequiredFieldValidators are displayed by noting the errors that are displayed in the ValidationSummary control and by hovering your pointer over each of the asterisks to see each tooltip. Test the user name validation by typing fewer than six characters into the TextBoxUserName control and clicking Register. Note the validation error. Also, try typing 15 or more characters. Next, type 10 characters into the field but use an invalid character such as the apostrophe ( ). Finally, type valid data into the text box to ensure that the validation control works properly. Test the email field by entering an invalid email address. Finally, test with a valid email address. Test the password field for the appropriate input by trying to input fewer than 6 characters or more than 14 characters. Also, attempt a password that is all lowercase, all uppercase, or all numeric. Notice that special characters, such as the plus sign (+), minus sign (-), and percent sign (%), are allowed in the password, but not required. Finally, attempt to enter a valid password. Test the confirmation password by typing a confirmation password that does not match the password. Test again with a matching password.

Many organizations create a corporate PowerPoint template in an effort to ensure that every presentation created in the organization has a similar graphical style. Although these templates can ensure a similar look across presentations, if they ignore the three research realities described in this chapter, they also diminish the effectiveness of presentations of all the presenters who use them.