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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.

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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.

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public interface IAuthorizationFilter { void OnAuthorization(AuthorizationContext filterContext); }

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); }

}

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:

If you wanted to create your own filter attribute for authentication or authorization, you could implement the IAuthorizationFilter interface as an action filter and apply it to an action. AuthorizeAttribute does its security check in the OnAuthorization method, and sets the AuthorizationContext s Result property to HttpUnauthorizedResult the mechanism for returning the 401 status code. There are several other IAuthorizationFilter implementations in ASP.NET MVC; all are used to short-circuit the normal response to protect against undesired requests. 9 covered filters, and these five filters deal specifically with security:

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

Set up content type specific blocks and assign them to regions. Do you have another content type to add such as a blog or forum Repeat steps 3 and 4. Set up the front page.

This asks for specific columns from the entity rather than the whole entity. This is legal ESQL, but it would fail at runtime in the context of Example 14-12. That example creates the query with a call to CreateQuery<SalesOrderHeader> on the object context. The generic type argument to CreateQuery SalesOrderHeader here indicates the type of result we re expecting from the query, but this modified query clearly returns something other than a SalesOrderHeader. It returns a couple of columns from each matching entity. When you build a query like this, you get back objects that implement IDataRecord a general-purpose interface used across all of ADO.NET to represent a record (such as a table row) whose columns might not be known until runtime. (This

Cross-site scripting (XSS)

is one of the interfaces listed in Table 14-1.) So you d need to use CreateQuery<IDataR ecord> to create such a query, and a suitably modified loop to extract the results:

var query = dbContext.CreateQuery<IDataRecord>( "SELECT o.TotalDue, o.OrderDate " + "FROM AdventureWorksLT2008Entities.SalesOrderHeaders AS o " + "WHERE o.OrderDate = @orderDate", new ObjectParameter("orderDate", orderDate)); foreach (var order in query) { Console.WriteLine(order["TotalDue"]); }

Even if you ask for the whole entity as a single column in the SELECT clause, for example:

We ve seen how AuthorizeAttribute can help us manage authentication and authorization, so now let s turn our attention to other, more insidious attack vectors. Although authentication and authorization checks prevent hapless visitors from accessing secure areas, we still must protect our application from hackers and thieves who attempt to exploit vulnerabilities inherent in web applications.