Data Cache in ASP. NET Cache

Add Cache [Key] = object or Cache. Insert

Remove Cache. Remove (key)

1. Directly write the value to the Cache

The code is as follows:	Copy code
HttpContext. Current. Cache ["One"] = "1 ";

Use the 'absolute expires' method to process the cache. The expiration time is December 31, 9999 (this method is not recommended and the cache Key should be cleared when appropriate)

2. Insert Cache using Insert (String, Object)

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String cacheKey = "Two "; Object cacheValue = HttpContext. Current. Cache. Get (cacheKey ); If (cacheValue = null) { CacheValue = WebConfigurationManager. ConnectionStrings ["ApplicationServices"]. ConnectionString; HttpContext. Current. Cache. Insert (cacheKey, cacheValue ); } // Display the Key and Value of the specified cache This. ShowMessage (cacheKey, cacheValue. ToString ());

3. Insert Cache using Insert (String, Object, CacheDependency, DateTime, TimeSpan)

The code is as follows:

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String cacheKey = "_ cache _ students "; DataSet dataSet = this. Cache. Get (cacheKey) as DataSet; If (dataSet = null) { DataSet = new DataSet (); // Load the XML file and fill it with DataSet DataSet. ReadXml (this. Server. MapPath (@ "XMLFile. xml ")); // Add the cache and set the 'absolute expiration time' to 5 minutes This. Cache. Insert (cacheKey, dataSet, null, DateTime. Now. AddMinutes (5), System. Web. Caching. Cache. NoSlidingExpiration ); } // Bind the DataGrid data GrdDefault. DataSource = dataSet; GrdDefault. DataBind ();

The two most important parameters of this method are absoluteExpiration and slidingExpiration.
AbsoluteExpiration DateTime type, representing the absolute expiration time
SlidingExpiration TimeSpan type, indicating the sliding expiration time
AbsoluteExpiration and slidingExpiration cannot be used simultaneously
For example, if the absoluteExpiration parameter is set, the slidingExpiration must be set to System. Web. Caching. Cache. NoSlidingExpiration.
If the slidingExpiration parameter is set, absoluteExpiration must be set to System. Web. Caching. Cache. NoAbsoluteExpiration.

4. Insert (String, Object, CacheDependency, DateTime, TimeSpan, CacheItemPriority,

The code is as follows:

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CacheItemRemovedCallback) insert Cache Public partial class PriorityAndCallbackDemo: System. Web. UI. Page { # Region static field Static bool CacheItemRemoved = false; Static CacheItemRemovedReason Reason; Static string CacheItemKey = "fw _ cache _ students "; # Endregion # Region Event Processing // Page loading Protected void Page_Load (object sender, EventArgs e)     { // The cache item has been removed. If (PriorityAndCallbackDemo. CacheItemRemoved)         { LtMessage. Text = string. Format ("Key = {0} has been removed from the cache because: {1}", PriorityAndCallbackDemo. CacheItemKey, PriorityAndCallbackDemo. Reason. ToString ());         }     } // Click "Add cache" to process the event. Protected void btnAddCache_Click (object sender, EventArgs e)     { DataSet dataSet = this. Cache. Get (PriorityAndCallbackDemo. CacheItemKey) as DataSet; If (dataSet = null)         { DataSet = new DataSet (); DataSet. ReadXml (this. Server. MapPath (@ "XMLFile. xml ")); // Use Web. config as the cache expiration dependency CacheDependency dependency = new CacheDependency (this. Server. MapPath (@ "Web. config"), DateTime. Now ); // Add the cache and set the priority to the default level This. cache. insert (PriorityAndCallbackDemo. cacheItemKey, dataSet, dependency, DateTime. now. addMinutes (1), System. web. caching. cache. noSlidingExpiration, CacheItemPriority. default, new CacheItemRemovedCallback (this. cacheItemRemovedHandler ));         } // Bind the GridView data GrdDefault. DataSource = dataSet; GrdDefault. DataBind ();     } // Click the 'remove cache' button to process the event. Protected void btnRemoveCache_Click (object sender, EventArgs e)     { If (this. Cache [PriorityAndCallbackDemo. CacheItemKey]! = Null)         { This. Cache. Remove (PriorityAndCallbackDemo. CacheItemKey );         }     } # Endregion # Region private method // Handle cache item removal events Private void CacheItemRemovedHandler (string key, object value, CacheItemRemovedReason relason)     { PriorityAndCallbackDemo. CacheItemRemoved = true; PriorityAndCallbackDemo. Reason = relason;     } # Endregion }

Two important parameters of this method are CacheItemPriority and CacheItemRemovedCallback.
CacheItemPriority indicates the priority of cache items. When the server memory is insufficient, items with a higher priority are not easily removed.
CacheItemRemovedCallback this parameter is of the delegate type. It is called when a cache item is removed. The Reason parameter is used to indicate the Reason why the cache item is removed.

[How do I use it]

First, understand the cache policy. You can call an expiration policy or an absolute expiration policy. Note: The two cannot be used at the same time.
 

To use the callable expiration policy, you need to set the absoluteExpiration = DateTime. MaxValue, TimeSpan. FromMinutes (10) item to be removed only if it is not used within 10 minutes.

The code is as follows:	Copy code
Cache. Insert ("data", "123", null, DateTime. MaxValue, TimeSpan. FromMinutes (10 ));

Absolute Strategy, such as weather report, to save information for 60 minutes

The code is as follows:	Copy code
Cache. Insert ("data", "123", null, DateTime. Now. AddMinutes (60), TimeSpan. Zero );

Cache dependency.

That is, the invalidation of a cache depends on another object. The object here can refer to another cache, or a file, or ....

Class: CacheDependency namespace System. Web. Caching. CacheDependency depends on other cache projects
 

The code is as follows:

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System. Web. Caching. CacheDependency cacheDependency = new System. Web. Caching. CacheDependency (null, new string [] {"time "}); Cache. Insert ("number", ++ num, cacheDependency );   Dependent on files or folders   System. Web. Caching. CacheDependency cacheDependency = new System. Web. Caching. CacheDependency ("test. xml "); Automatically removed from the cache when the test. xml file is deleted or updated   System. Web. Caching. CacheDependency cacheDependency = new System. Web. Caching. CacheDependency (null, new string [] {"time "}); Cache. Insert ("test", "123", cacheDependency );   Remove project callback Cache. Insert ("test", "123", null, DateTime. Now. AddSeconds (10), TimeSpan. Zero, new CacheItemUpdateCallback (Test ));     Private void Test (string key, CacheItemUpdateReason reason, out object expensiveObject, out CacheDependency dependency, out DateTime absoluteExpiration, out TimeSpan slidingExpiration)     {       }