ASP.NET 2.0: A Developeramp;#039;s Notebook [Electronic resources] نسخه متنی

4.5. Cache the Data Source Control

Note: To improve the performance of your application, you should
cache the data source control if you are using one.

Performing database access is a
time-consuming operation; therefore, it is important that you reduce
the number of times you connect to the database. The SqlDataSource
control (as well as the AccessDataSource control) supports caching of
data. Caching of the data source controls is useful in cases when
your data does not change oftenfor example, when you have
pages displaying product listings and information.

4.5.1. How do I do that?

To see how to enable caching of data source controls in your
application, you will build an application in this lab that uses a
SqlDataSource control to retrieve rows from the authors table in the
pubs database and then uses the GridView control to display them. The
SqlDataSource control will be cached for 60 seconds before the cache
is invalidated.

Note: In general, the more static your data, the longer the time
you should cache your data.

Launch Visual Studio 2005 and create a new web site project. Name the
project C:\ASPNET20\chap04-DataSourceCache.

Drag and drop a GridView control onto the default Web Form and
configure it to use a SqlDataSource control to connect to the pubs
database in SQL Server 2005 Express (see the lab Section 4.1 for detailed instructions on
how to do this). In particular, the au_id, au_fname, and au_lname
fields are retrieved. The Source View of the GridView and
SqlDataSource control looks like Example 4-4.

Example 4-4. Source View of the GridView and SqlDataSource controls

<asp:GridView ID="GridView1" runat="server" 
DataSourceID="SqlDataSource1" 
AutoGenerateColumns="False"
DataKeyNames="au_id">
<Columns>
<asp:BoundField ReadOnly="True" HeaderText="au_id" 
DataField="au_id" SortExpression="au_id">
</asp:BoundField>
<asp:BoundField HeaderText="au_lname" 
DataField="au_lname" SortExpression="au_lname">
</asp:BoundField>
<asp:BoundField HeaderText="au_fname" 
DataField="au_fname" SortExpression="au_fname">
</asp:BoundField>
</Columns>
</asp:GridView>
<asp:SqlDataSource ID="SqlDataSource1" runat="server" 
SelectCommand="SELECT [au_id], [au_lname], 
[au_fname] FROM [authors]"
ConnectionString="<%$ ConnectionStrings:
pubsConnectionString %>">
</asp:SqlDataSource>

To enable caching of the
SqlDataSource control, set the CacheDuration (in seconds) and
EnableCaching attributes, as shown in the following code snippet:

<asp:SqlDataSource ID="SqlDataSource1" runat="server" 
SelectCommand="SELECT [au_id], [au_lname], 
[au_fname] FROM [authors]"
ConnectionString="<%$ ConnectionStrings:pubsConnectionString %>"
CacheDuration="60" 
EnableCaching="True"
CacheExpirationPolicy="Absolute" >
</asp:SqlDataSource>

Press F5 to test the application. To verify that the data in the
SqlDataSource control is cached, modify one of the rows in the
authors table and refresh the page. You will notice that the data in
the GridView control is not updated until approximately one minute
(60 seconds) later.

The default cache expiration policy is that of
absolute, which means that the data cached by the
data source control will expire x seconds (as
specified in the CacheDuration attribute) after the data source has
been loaded.

4.5.2. What about...

...sliding cache policy?

In the sliding cache policy, the cache will expire if a request is
not made within a specified duration. For
example, the following code specifies that the cache will have a
sliding duration of one minute. If a request is made 59 seconds after
the cache is accessed, the validity of the cache would be reset to
another minute. Sliding expiration policy is useful whenever you have
a large number of items to cache, since this policy enables you to
keep only the most frequently accessed items in memory.

<asp:SqlDataSource ID="SqlDataSource1" runat="server" 
SelectCommand="SELECT [au_id], [au_lname], 
[au_fname] FROM [authors]"
ConnectionString="<%$ ConnectionStrings:pubsConnectionString %>"
CacheDuration="60" 
EnableCaching="True"
CacheExpirationPolicy="Sliding" >
</asp:SqlDataSource>

4.5.3. Where can I learn more?

For a good discussion on implementing page caching in ASP.NET using absolute
expiration, check out the article at:

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnpatterns/html/ImpPageCacheInASP.asp.

You will also learn how to cache fragments of a page in Chapter 6.