.NET/ASP.NET/C#/VB.NET PDF Document SDK

private void DiscardAnyOldCacheEntries() { // Calling ToList() on source in order to query a copy // of the enumeration, to avoid exceptions due to calling // Remove in the foreach loop that follows. var staleKeys = from entry in cachedRecords.ToList() where IsStale(entry.Value) select entry.Key; foreach (int staleKey in staleKeys) { cachedRecords.Remove(staleKey); } }

11.1.1 Requiring authentication with AuthorizeAttribute The simplest use of AuthorizeAttribute, shown in listing 11.1, only requires that the current user be authenticated.

But it s also possible to create new dictionaries with LINQ queries. Example 9-11 illustrates how to use the standard ToDictionary LINQ operator.

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Click the Administer link in the Management menu to navigate to the main administrative section of the site. Everything you need to manage your site should be within one or two clicks of this page. You ll notice that the title for each box corresponds to a link in the upper section of the administration toolbar; you ll see appearance, people, modules, and so on (see Figure 1-5). This is by design; the administrative section simply displays links and link descriptions from the administration toolbar. This means you have several ways to access the dashboard and other administrative areas.

IDictionary<int, string> buildingIdToNameMap = MyDataSource.Buildings.ToDictionary( building => building.ID, building => building.Name);

[Authorize] public ActionResult About() { return View(); }

This example presumes that MyDataSource is some data source class that provides a queryable collection containing a list of buildings. Since this information would typically be stored in a database, you would probably use a database LINQ provider such

as LINQ to Entities or LINQ to SQL. The nature of the source doesn t greatly matter, though the mechanism for extracting the resources into a dictionary object are the same in any case. The ToDictionary operator needs to be told how to extract the key from each item in the sequence. Here we ve provided a lambda expression that retrieves the ID property again, this property would probably be generated by a database mapping tool such as the ones provided by the Entity Framework or LINQ to SQL. (We will be looking at data access technologies in a later chapter.) This example supplies a second lambda, which chooses the value here we pick the Name property. This second lambda is optional if you don t provide it, ToDictionary will just use the entire source item from the stream as the value so in this example, leaving out the second lambda would cause ToDictionary to return an IDictionary<int, Building> (where Building is whatever type of object MyDataSource.Buildings provides). The code in Example 9-11 produces the same result as this:

var buildingIdToNameMap = new Dictionary<int, string>(); foreach (var building in MyDataSource.Buildings) { buildingIdToNameMap.Add(building.ID, building.Name); }

When this action is requested by an unauthenticated user, AuthorizeAttribute, applied to the About action B, will prevent access to it.

HashSet<T> is a collection of distinct values. If you add the same value twice, it will ignore the second add, allowing any given value to be added only once. You could use

Figure 1-5. Click the Administer link in the Management menu to navigate to the main administration section of the site. The two links at the top right of the page directly below the administration toolbar (TASKS and INDEX) are called tabs (see Figure 1-6). Tabs are used in certain administration pages to provide additional configuration options. In the main administration section, for example, these tabs allow you to view a highlevel overview of configuration options available or view an index of all configuration options. I recommend using the INDEX page of the administrative section to configure your site when you first start using Drupal to help build your knowledge of how Drupal works. You ll also notice a circular icon with an X in the center; click this icon to close the administration section.

this to ensure uniqueness for example, imagine an online chat server. If you wanted to make sure that usernames are unique, you could maintain a HashSet<string> of usernames used so far, and check that a new user s chosen name isn t already in use by calling the hash set s Contains method.

11.1.2 Requiring authorization with AuthorizeAttribute To restrict an action further, developers can specify users or roles that AuthorizeAttribute requires. These roles or users are passed to the attribute using a commadelimited list of strings containing either the usernames or the roles allowed. Listing 11.2 shows the AuthorizeAttribute syntax for requiring a specific user.

You might notice that List<T> offers a Contains method, and so with a little extra code, you could implement a uniqueness check using List<T>. However, HashSet<T> uses the same hash-code-based fast lookup as a dictionary, so HashSet<T> will be faster for large sets than List<T>.