ASP.NET PDF Viewer using C#, VB/NET

It s not a scenario C# attempts to help you with you end up having to construct the expression trees without the compiler s assistance This is not for the fainthearted).

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To test these methods, divide the tests into three sections: one for testing tags, one for testing images, and one for testing the images from tag associations. These three sections can be seen as slots in the unit test class declaration shown in Listing 16-22. The class contains a private member function called pixelCompareImages. It is used to ensure that two images are exactly identical, pixel by pixel. It is needed to see whether an image is properly stored in the database. Listing 16-22. The unit test class for testing the ImageCollection class class ImageCollectionTest : public QObject { Q_OBJECT private slots: void testTags(); void testImages(); void testImagesFromTags(); private: bool pixelCompareImages( const QImage &a, const QImage &b ); };

The practice of stitching together strings to form dynamic queries is messy and can be fraught with security issues such as injection attacks. It s occasionally useful if you understand the risks and can mitigate them, but you need to exercise extreme caution.

And in case you re wondering about LINQ to XML, that doesn t help here. It lets you use LINQ-capable languages like C# or VB.NET to write LINQ queries to look in an XML document. It doesn t let you put LINQ queries in an XML document.

Of course, string-based queries have a massive downside compared to LINQ: the C# compiler cannot offer any help as it doesn t understand ESQL. If your ESQL strings are badly formed, you only get to find that out at runtime. And even if your ESQL is syntactically correct, C# does not understand the relationship between it and your code whereas with a LINQ to Entities query C# can detect things such as type mismatches, it won t spot when your ESQL gets out of sync with the code that uses the results. Besides the inherent benefits and disadvantages of a string-based query, there s also the fact that ESQL is, in effect, the native query language for the EF. This means there are a few EF features that can be accessed only through ESQL, although they re all somewhat arcane. For example, an ESQL query can navigate associations between entities even if you ve neglected to define navigation properties to represent those associations. Example 14-12 shows a simple example that illustrates the basic use of ESQL.

Listing 16-23 shows the testTags test slot implementation. The tests performed are simple, and the procedure is the following: 1. Make sure that there are no tags from the start tests getIds. 2. Add one image and ensure that the image is in the collection tests addImage.

using (var dbContext = new AdventureWorksLT2008Entities()) { DateTime orderDate = new DateTime(2004, 6, 1); var query = dbContext.CreateQuery<SalesOrderHeader>("SELECT VALUE o " + "FROM AdventureWorksLT2008Entities.SalesOrderHeaders AS o " + "WHERE o.OrderDate = @orderDate", new ObjectParameter("orderDate", orderDate)); foreach (var order in query) { Console.WriteLine(order.TotalDue); }

The problem, of course, with this abstraction was that it was relatively simple and not originally designed or implemented for anything more complex than laying out and formatting text and graphics I am, of course, referring to Hypertext Markup Language (HTML) This specification, implemented by a browser, meant that simple text could be placed on a server, transferred from a server, interpreted by a browser, and laid out in a far more pleasing way than simple green-on-black on a page, giving the user a better experience More important, however, it could generate a whole new breed of application developers; all a developer had to do for an online, connected application to have a graphical experience was to generate it as HTML, and the browser would do the rest.

}

This has the same effect as Example 14-3, but using ESQL in place of a LINQ query. While this looks similar to a typical SQL query, the VALUE keyword is specific to ESQL. We use this to indicate that we don t want the usual column-like behavior of SQL. You can write a more traditional-looking query in ESQL, such as:

SELECT o.TotalDue, o.OrderDate FROM AdventureWorksLT2008Entities.SalesOrderHeaders AS o WHERE o.OrderDate = @orderDate

3 Add one tag to the image and verify that the collection contains one tag tests addTag and getTags 4 Add one more tag to the image and verify that the collection contains two tags tests addTag and getTags 5 Add one more tag to the image and verify that the collection contains three tags tests addTag and getTags 6 Add a duplicate tag to the image and verify that the collection contains three tags tests addTag and getTags 7 Add a new tag to a nonexistent image and verify that the collection contains three tags tests addTag and getTags In the listing, you can see that the ImageCollection object is created and then the tests are carried out.