caching application block used with xml and dataset

Introduction:

Microsoft introduced Enterprise Library in January 2005. Many companies have migrated their code from the independent Application Blocks to the Enterprise Library Blocks. In this article I will introduce the Caching application block which is part of one of the blocks shipped with Enterprise Library.

Adding the reference:

First thing you need to do is to add a reference to the dynamic link library. In order to use Caching Application Block you should make a reference to Microsoft.Practices.Enterprise.Caching.

Than you have to add the namespace to your C# code file.

using Microsoft.Practices.EnterpriseLibrary.Caching;

After this we are ready to use the Caching Application Block of the Enterprise Library.

Using Enterprise Library Caching Application Block:

Let's see how we can return dataset from the cache object to the calling block. We will see the code in small pieces so that you can easily understand it.

First of all we have to make the CacheManager object which is responsible for adding cache features to our application.

private CacheManager myCache;

Next, we make a method "LoadData()" which will return the dataset. We have to make it efficient that's why we will be checking that if the data is already present in the cache. If the data is present than we don't need to disturb the database access layer. First let's get the DataSet from the Cache object.

DataSet ds = (DataSet) myCache.GetData("MyData");

The above line is very similar to the line below:

DataSet ds = (DataSet) myCache["MyData"];

Next we have to check that if the Cache object is empty or not. If its empty than we need to go to the database and fetch a fresh copy of the DataSet.

if(ds!=null) { return ds; }

Now let's see that what happens if the Cache object is null.

else { Database db = DatabaseFactory.CreateDatabase(); DBCommandWrapper selectCommandWrapper = db.GetSqlStringCommandWrapper("SELECT * FROM Articles"); ds = db.ExecuteDataSet(selectCommandWrapper); myCache.Add("MyData",ds,CacheItemPriority.Normal,null,new Microsoft.Practices.EnterpriseLibrary.Caching .Expirations.AbsoluteTime(TimeSpan.FromMinutes(5)));   return (DataSet) myCache.GetData("MyData"); }

First we create a Database object which gets its configuration settings from the dataConfiguration.config file. Later we are executing a simple query which selects all rows from the table Articles. 

myCache.Add("MyData",ds,CacheItemPriority.Normal,null,new Microsoft.Practices.EnterpriseLibrary.Caching .Expirations.AbsoluteTime(TimeSpan.FromMinutes(5)));

Next we are adding the dataset to the Cache object using the CacheManager Add method. There are several parameters that we need to know. First is the key which we have set to "MyData". Next is the DataSet itself, then comes priority, refresh and finally the expiration policy. You can set expiration policy in different ways. I have used absolute expiration which means that the cache will expire after 5 minutes from the time that it was created. If you want to check this you can simply place a Response.Write line to display the time at which the cache is being recreated. And you will notice that the cache recreates itself after 5 minutes.

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There are some other different types of expirations that you can use. In the code below I am using SlidingExpiration policy.

myCache.Add("MyData",ds,CacheItemPriority.Normal,null,new Microsoft.Practices.EnterpriseLibrary.Caching.Expirations .SlidingTime(TimeSpan.FromMinutes(2)));

We have sliding time of 2 minutes this means that if the cache is not being accessed for 2 minutes than it will expire. On the other hand if the cache is accessed within 2 minutes than the time of the cache will be reset to 2 minutes. Meaning that the cache object will again get its sliding time of 2 minutes.

You can also set the expiration policy dependent on the file. This means that whenever a file is being changed the cache object will automatically gets the latest copy of that file. In the code below I am setting the file Dependency to the MyXmlFile.xml. This means that anytime the xml file changes than the cache data will be updated.

myCache.Add("MyData",ds,CacheItemPriority.Normal,null,new Microsoft.Practices.EnterpriseLibrary.Caching.Expirations .FileDependency(Server.MapPath("MyXmlFile.xml")));

You can also set the expiration policy to expire the cache at exact time and day. I don't know if anyone is going to use this option but here is the syntax for using it. Please check the ExtendedFormatTime format which can be found in ExtendedFormatTime.cs file provided by the Caching Application Block.

myCache.Add("MyData",ds,CacheItemPriority.Normal,null,new Microsoft.Practices.EnterpriseLibrary.Caching.Expirations .ExtendedFormatTime("* * * * 0 0 "));

Removing Cache Items:

You can easily remove the items from the cache using the Remove Method. The code below will remove once cache object from the cache collection. This removal is based on key which in this case is "MyData".

myCache.Remove("MyData");

If you want to remove all the items in the cache collection than you can simply use the flush method.

myCache.Flush();

Checking if the key is already present in the caching collection:

If you want to know that if a particular key is present in the cache than you can easily use the contains method of the CacheManager object.

myCache.Contains("MyData");

I hope you enjoyed the article, Happy programming !

转载于:https://www.cnblogs.com/xianqingzh/archive/2009/05/08/1452934.html