PHP中的数据库类; 只有一个功能 - 关于实践的问题以及是否是一个好主意

Question

So I have this database class in PHP and I only have 1 function in it (other than __construct and __destruct. Let me explain further...

I had originally written it so when I connected to a database I would just call my function connect_to_db() which returned a mysqli object. I then used this objects functions (->query(), ->prepare(), ->bind_param(), et cetera..) to do whatever. This cluttered (and still is as I haven't switched my code over to my new class yet) with a lot of functions that just do specific things, for example:

function get_country_info($db, $usrid) {
  $statement = "select `name`, `population`, `money`, `food` from `countries` where `usr_id` = ?";
  $qry = $db->prepare($statement) or
    trigger_error("get_country_info():statement failed...");
  $qry->bind_param("i", $usrid);
  $qry->execute();
  $qry->bind_result($name, $population, $money, $food);
  $qry->fetch();
  $res = array("name" => $name, 
    "pop" => $population, 
    "money" => $money, 
    "food" => $food);

  return $res;
}

And what I originally planned to do was just to throw these into a class for clarity, but what I actually ended up doing was creating a class that when created creates a mysqli object for a specific database (supplied via an argument) and when destroyed closes off this link. I very much like not having to worry about typing $db->close(); as when the script finishes executing the connection is closed.

It only has 1 other function; query(). This function can handle any query put forth and outputs it as a multidimensional array. It uses eval(). From what I understand this is generally frowned upon - but eval() is so useful; so why is it frowned upon?

I guess the function may be slow, but seen as I'm just using it for a pet project (browser based country management game) and I haven't noticed anything I'm not worried about that at all. What I am worried about is whether people would generally do this in the 'real world' or whether there is some sort of standard by which people do this, or perhaps something included (or add-on-able) in PHP which is usually used?

I'm self taught, so sometimes I don't really know the best way to go about doing things. Perhaps somebody could advise me here?

The function in question can be seen here: http://pastebin.org/353721, as its ~60 lines and I don't want to clutter the page. I also haven't extensively tested it (I don't even know what unit tests are, so I test by using the function in a lot of different ways) so it may have problems I'm not aware of that you guys can point out.

Thanks.

Answer 1

Doesn't seem to me too bad. You have basically done a really basic wrapper around the database, and you performed the very first step in database independence, which is good.

This can be good for small and well organized projects, but once you will start going more complicated, you will soon notice that your approach has one large disadvantage: you still have your SQL queries split around the site. The day you will change anything in the database, you'll need to go through all your site and look for all the SQL statements: this is bad (I had to do it once...).

You should now move all the SQL code to one place. So there are various options. In a similar context, I made the query() method protected, then made the Db class "abstract" and subclassed it. Each subclass is a class which contains several methods relative to a specific set of tables, and this is the only place where you find SQL. All the rest of the project can only call these methods.

Or, even better, you could use an ORM (oblect relational mapper) which would map each table to an object.

For what concerns the evils of evals: I never used them. But I thought I wasn't going to use a "goto" because it's evil, and then I found the magic place where that was the perfect fit. So, if you have investigated all the possibilities, and you think that's the optimal solution... use it.