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>Chapter 14. Caching</TD
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><H1
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><A
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></A
>Multiple Caches Per Page</H1
><P
> You can have multiple cache files for a single call to
<A
HREF="api.display.html"
><TT
CLASS="varname"
>display()</TT
></A
>
or <A
HREF="api.fetch.html"
><TT
CLASS="varname"
>fetch()</TT
></A
>.
Let's say that a call to <TT
CLASS="literal"
>display('index.tpl')</TT
> may have
several different output contents depending on some condition, and you want
separate caches for each one. You can do this by passing a
<TT
CLASS="parameter"
><I
>$cache_id</I
></TT
> as the second parameter to the
function call.
</P
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><TR
><TD
><DIV
CLASS="example"
><A
NAME="AEN6758"
></A
><P
><B
>Example 14-6. Passing a $cache_id to display()</B
></P
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><TD
><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br /></span><span style="color: #007700">require(</span><span style="color: #DD0000">'Smarty.class.php'</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">$smarty </span><span style="color: #007700">= new </span><span style="color: #0000BB">Smarty</span><span style="color: #007700">;<br /><br /></span><span style="color: #0000BB">$smarty</span><span style="color: #007700">-></span><span style="color: #0000BB">caching </span><span style="color: #007700">= </span><span style="color: #0000BB">1</span><span style="color: #007700">;<br /><br /></span><span style="color: #0000BB">$my_cache_id </span><span style="color: #007700">= </span><span style="color: #0000BB">$_GET</span><span style="color: #007700">[</span><span style="color: #DD0000">'article_id'</span><span style="color: #007700">];<br /><br /></span><span style="color: #0000BB">$smarty</span><span style="color: #007700">-></span><span style="color: #0000BB">display</span><span style="color: #007700">(</span><span style="color: #DD0000">'index.tpl'</span><span style="color: #007700">, </span><span style="color: #0000BB">$my_cache_id</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">?></span>
</span>
</code></TD
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><P
> Above, we are passing the variable <TT
CLASS="literal"
>$my_cache_id</TT
> to
<A
HREF="api.display.html"
><TT
CLASS="varname"
>display()</TT
></A
>
as the <TT
CLASS="parameter"
><I
>$cache_id</I
></TT
>. For each unique value of
<TT
CLASS="literal"
>$my_cache_id</TT
>, a separate cache will be
generated for <TT
CLASS="filename"
>index.tpl</TT
>. In this example,
<TT
CLASS="literal"
>article_id</TT
> was passed in the
URL and is used as the <TT
CLASS="parameter"
><I
>$cache_id</I
></TT
>.
</P
><DIV
CLASS="note"
><BLOCKQUOTE
CLASS="note"
><P
><B
>Technical Note: </B
>
Be very cautious when passing values from a client (web browser) into
Smarty or any PHP application. Although the above example of using the
article_id from the URL looks handy, it could have bad consequences. The
<TT
CLASS="parameter"
><I
>$cache_id</I
></TT
> is used to create a directory on the file
system, so if the user
decided to pass an extremely large value for article_id, or write a script
that sends random article_id's at a rapid pace, this could possibly cause
problems at the server level. Be sure to sanitize any data passed in before
using it. In this instance, maybe you know the article_id has a length of
ten characters and is made up of alpha-numerics only, and must be a valid
article_id in the database. Check for this!
</P
></BLOCKQUOTE
></DIV
><P
> Be sure to pass the same <TT
CLASS="parameter"
><I
>$cache_id</I
></TT
> as the
second parameter to
<A
HREF="api.is.cached.html"
><TT
CLASS="varname"
>is_cached()</TT
></A
> and
<A
HREF="api.clear.cache.html"
><TT
CLASS="varname"
>clear_cache()</TT
></A
>.
</P
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><TR
><TD
><DIV
CLASS="example"
><A
NAME="AEN6780"
></A
><P
><B
>Example 14-7. Passing a cache_id to is_cached()</B
></P
><TABLE
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><TD
><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br /></span><span style="color: #007700">require(</span><span style="color: #DD0000">'Smarty.class.php'</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">$smarty </span><span style="color: #007700">= new </span><span style="color: #0000BB">Smarty</span><span style="color: #007700">;<br /><br /></span><span style="color: #0000BB">$smarty</span><span style="color: #007700">-></span><span style="color: #0000BB">caching </span><span style="color: #007700">= </span><span style="color: #0000BB">1</span><span style="color: #007700">;<br /><br /></span><span style="color: #0000BB">$my_cache_id </span><span style="color: #007700">= </span><span style="color: #0000BB">$_GET</span><span style="color: #007700">[</span><span style="color: #DD0000">'article_id'</span><span style="color: #007700">];<br /><br />if(!</span><span style="color: #0000BB">$smarty</span><span style="color: #007700">-></span><span style="color: #0000BB">is_cached</span><span style="color: #007700">(</span><span style="color: #DD0000">'index.tpl'</span><span style="color: #007700">,</span><span style="color: #0000BB">$my_cache_id</span><span style="color: #007700">)) {<br /> </span><span style="color: #FF8000">// No cache available, do variable assignments here.<br /> </span><span style="color: #0000BB">$contents </span><span style="color: #007700">= </span><span style="color: #0000BB">get_database_contents</span><span style="color: #007700">();<br /> </span><span style="color: #0000BB">$smarty</span><span style="color: #007700">-></span><span style="color: #0000BB">assign</span><span style="color: #007700">(</span><span style="color: #0000BB">$contents</span><span style="color: #007700">);<br />}<br /><br /></span><span style="color: #0000BB">$smarty</span><span style="color: #007700">-></span><span style="color: #0000BB">display</span><span style="color: #007700">(</span><span style="color: #DD0000">'index.tpl'</span><span style="color: #007700">,</span><span style="color: #0000BB">$my_cache_id</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">?></span>
</span>
</code></TD
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></TD
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><P
> You can clear all caches for a particular <TT
CLASS="parameter"
><I
>$cache_id</I
></TT
>
by passing <TT
CLASS="constant"
>NULL</TT
> as the
first parameter to
<A
HREF="api.clear.cache.html"
><TT
CLASS="varname"
>clear_cache()</TT
></A
>.
</P
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CLASS="EXAMPLE"
><TR
><TD
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CLASS="example"
><A
NAME="AEN6788"
></A
><P
><B
>Example 14-8. Clearing all caches for a particular $cache_id</B
></P
><TABLE
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BGCOLOR="#E0E0E0"
CELLPADDING="5"
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><TD
><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br /></span><span style="color: #007700">require(</span><span style="color: #DD0000">'Smarty.class.php'</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">$smarty </span><span style="color: #007700">= new </span><span style="color: #0000BB">Smarty</span><span style="color: #007700">;<br /><br /></span><span style="color: #0000BB">$smarty</span><span style="color: #007700">-></span><span style="color: #0000BB">caching </span><span style="color: #007700">= </span><span style="color: #0000BB">1</span><span style="color: #007700">;<br /><br /></span><span style="color: #FF8000">// clear all caches with "sports" as the $cache_id<br /></span><span style="color: #0000BB">$smarty</span><span style="color: #007700">-></span><span style="color: #0000BB">clear_cache</span><span style="color: #007700">(</span><span style="color: #0000BB">null</span><span style="color: #007700">,</span><span style="color: #DD0000">'sports'</span><span style="color: #007700">);<br /><br /></span><span style="color: #0000BB">$smarty</span><span style="color: #007700">-></span><span style="color: #0000BB">display</span><span style="color: #007700">(</span><span style="color: #DD0000">'index.tpl'</span><span style="color: #007700">,</span><span style="color: #DD0000">'sports'</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">?></span>
</span>
</code></TD
></TR
></TABLE
></DIV
></TD
></TR
></TABLE
><P
> In this manner, you can <SPAN
CLASS="QUOTE"
>"group"</SPAN
> your caches together by giving
them the same <TT
CLASS="parameter"
><I
>$cache_id</I
></TT
>.
</P
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