在PHP中调用数据库中的函数

Question

I have this requirement that states that I must have a function signature as a value in a database column. So what I need to do is get that value that will then call the function in code. For example....let's say I have a column in a database named "Signature" that has a value of SendMail();. I need to be able to get the return value and then store it in another table. The problem is when I use the eval function on $i['Signature'] the function gets called, but I can't get the return value. What am I doing wrong? Here's an example:

$query = "SELECT signature FROM tbl WHERE id = 1 ";
$signature = mysql_query($query);
while ($i = mysql_fetch_array($signature)){
   //Here the function is being called properly but I can't get the return value.
   $email= eval($i['Signature']);
   if(mysql_num_rows($i) == 0){
      //insert the returned value into another table.
      $insertString = "INSERT INTO tbl (email) VALUES ('$email')";
   }
}

function SendMail()
{
   $email= 'Have a great day'
   return $email;
}

Also I'm bound to get some "eval is evil" comments, so if there's a better way please advise.

Answer 1

from the docs

eval() returns NULL unless return is called in the evaluated code, in which case the value passed to return is returned. 

Therefore you should add return:

$email= eval('return ' . $i['Signature']);

alternatively:

eval('$email = '  . $i['Signature']);