Implementing a Template Based Web Site With PHP

Implementing a Template Based Web Site With PHP - The PHP Code
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Our demonstration PHP page is going to return the HTML for ResultsPage, along with a table full of results (with title and hits columns) using the information from the database. If you want to create the table and dummy data for the database, use the following MySQL statement:

CREATE TABLE items (

id int unsigned NOT NULL AUTO_INCREMENT PRIMARY KEY,

title varchar(30) NOT NULL,

hits int NOT NULL DEFAULT '',

);

INSERT INTO items (title,hits) VALUES ('Test Item 1',29),('Test Item 2',15),('Test Item 3',0);

Lets now take a look at the PHP code required to do this:

<?

#set the page title and query

$pagetitle = "Search Results";

$searchquery = "Dummy search";

#get the database information

$query = mysql_query("SELECT title,hits FROM items ORDER BY hits DESC LIMIT 10")

#loop through the results

while ($data=mysql_fetch_array($query)) {

#load the template for this instance, appending the data onto $resultbits

eval("\$resultbits .= \"".gettemplate("ResultsBit")."\";");

}

#now return the whole template

eval("echo \"".gettemplate("ResultsPage")."\";");

?>

The code is actually very simple: it sets a few variables, loads the data from a template, and then outputs the data. However, it's those eval statements that do all the hard work and need looking at more closely.

Lets take a look at

eval("\$resultbits .= \"".gettemplate("ResultsBit")."\";");

first. What the eval statement does is evaluate PHP code as if you have written it yourself. For example

eval("echo \"thetext\";");

does the same as hard-coding

echo "thetext";

Our code takes advantage of this functionality, by writing it's own php code for this statement. What's the point, you may ask? Well, just as

echo "hello $name";

would output hello and the contents of the variable, $name, the same applies when used within an eval statement. Lets imagine that the gettemplate function returns simply

<td>$data[title]</td>

What ends up being evaluated in the call to the eval statement is (remembering that we need to escape characters such as $ and " within the string):

$resultbits .= "<td>$data[title]</td>";

PHP then appends <td>$data[title]</td> to the $resultbits variable, and replaces $data[title] with its current value. In the same way, PHP replaces all the variables within our template with the current value, which, in this instance, has been loaded from $data=mysql_fetch_array($query).

Our code simply loops through the information from the database, evaluating the template for each different value of $data[title] and appending that value to $resultbits. Finally, once the loop is complete, we call another eval statement, this time retrieving the value from the ResultsPage template and replacing $pagetitle, $searchquery and $resultbits with their values in the script. Simple.
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