In a file, I connect to the database (using PDO) and the resulting connection is called $db, so that queries I run would be something like
$db->query("SELECT money FROM bank_accounts");
However, if I put that line in a function, $db isn't defined so it doesn't work.
Obviously reconnecting to the database in each function isn't the best way to accomplish db calls in a function so how would I accomplish something like
function stealMoney($acctID) {
$db->query("SELECT money FROM bank_accounts WHERE accountID = $acctID");
}
You need to use $db in a function.
And its not defined in the function, so definitely, $db is inaccessible/undefined to the function body.
There are two ways to deal it:
1) Pass $db as an argument to the function.
So, the function body becomes:
function stealMoney($acctID, $db = NULL) {
$db->query("SELECT money FROM bank_accounts WHERE accountID = $acctID");
}
And the function call:
stealMoney($acctID, $db);
2) Use global:
In this case, you can use $db as a global.
So, the function body becomes:
function stealMoney($acctID) {
global $db;
$db->query("SELECT money FROM bank_accounts WHERE accountID = $acctID");
So that, your function will read this variable from outside and can access it.
Related
I have come to the conclusion that using mysqli in an OO approach is better than a procedural approach. (Source: Why is object oriented PHP with mysqli better than the procedural approach?). But I'm not quite sure if what I am doing is really all that more efficient than what I was doing before.
I have a function that runs sql queries. This is what my block of code looked like:
Database connection:
function connectDB(){
$con = mysqli_connect(server, username, password, database);
return $con;
}
Query function:
function executeQuery($payload){
$con = connectDB;
$result = mysqli_query($con, $payload);
return $result;
}
As you can see, that's not very efficient because I'm creating a new database connection every time executeQuery is called. So I figured I'd try it using OOP.
Database connection (OOP):
function connectDB(){
$con = new mysqli(server, username, password, database);
return $con;
}
Database query (OOP):
function executeQuery($payload){
$con = connectDB();
$result = $con->query($payload);
return $result;
}
Now to me, it seems that I am obviously doing something wrong. Each time a query is called I am re-instantiating the mysqli class and I assume that mean's that I am making another database connection.
So how do I do this properly and efficiently?
So how do I do this properly and efficiently?
This really has nothing to do with using MySQLi in a procedural versus OOP way.
What this has to do with is the following line:
$con = connectDB();
This will recreate the database connection on every query. Which, as you noted, is not efficient.
There are many ways to solve this. For example:
Use the mysqli class directly.
Pass $con to executeQuery() (Dependency Injection)
Create a DB class with both connectDB() and executeQuery().
I usually use mysqli directly as I see no reason to wrap the native class. I create the connection object globally (in a config file) and use Dependency Injection when other objects/functions need it.
Although your procedural approach can be solved pretty easily
function connectDB(){
return mysqli_connect(server, username, password, database);
}
function executeQuery($payload){
static $con;
id (!$con)
{
$con = connectDB();
}
return $con->query($payload);
}
an OOP approach would be indeed better. I am not an OOP pro, but you can take a look at my approach which at least using encapsulation to hide all the dirty job inside and provide concise methods to get the data already in desired format like this:
// to get a username
$name = $db->getOne('SELECT name FROM table WHERE id = ?i',$_GET['id']);
// to get an array of data
$data = $db->getAll("SELECT * FROM ?n WHERE mod=?s LIMIT ?i",$table,$mod,$limit);
// to get an array indexed by id field
$data = $db->getInd('id','SELECT * FROM ?n WHERE id IN ?a','table', array(1,2));
// to get a single dimensional array
$ids = $db->getCol("SELECT id FROM tags WHERE tagname = ?s",$tag);
// a simple code for the complex INSERT
$data = array('offers_in' => $in, 'offers_out' => $out);
$sql = "INSERT INTO stats SET pid=?i,dt=CURDATE(),?u ON DUPLICATE KEY UPDATE ?u";
$db->query($sql,$pid,$data,$data);
As a solution for your exact problem : "You do not want to instantiate a new MySQL connection for each time a query is executed" ,
Well, we can think about the following :
You need to make your connection variable ($con) in GLOBAL scope, such that when accessed through any function you can grab THAT variable you set before, not instantiate a new one.
we can do this using keyword "global" , as following :
The connection function :
function &connectDB(){
global $con;
if(empty($con)) {
$con = new mysqli(server, username, password, database);
}
return $con;
}
And for more performance , we avoid cloning/copying the connection variable/resource by using reference function ( &connectDB ),
Query Execution function
Now we've set the connection function in a flexible way , to set the queryExecution function , we can use more than one solution :
First solution :
function executeQuery($payload){
$con = &connectDB(); // do not forget the () , it's good practice
return $con->query($payload);
}
In this solution we made use of "reference" , so the expression :
$con = &connectDB();
will set the variable $con as a reference/shortcut for global $con (i.e : just pointing to the global variable $con)
or
Second solution :
function executeQuery($payload){
global $con;
return $con->query($payload);
}
but for the second solution : Function "connectDB()" MUST be called at least once before any calling to "executeQuery()", In order to make sure that there a connection has been established with the database,
Keep in mind that, according to this solution , calling "connectDB()" more than once will not create more than one connection , once it is called , connection is created, if called again it will return the PREVIOUSLY created connection.
Hope it helps :)
by the way : stay with the OOP approach for database connection , it has much more benefits over the procedural ways,
& I recommend using PDO, it is much more portable.
OK, I see some similar questions to mine, but their examples all use PHP classes...mine does not. Maybe that's the problem? I shouldn't need classes because my site is exceedingly simple at this point in time.
Anyway, I'm trying to use PDO to connect to a MySQL db. I connect to the db fine in a file called config.php, and include this file in index.php with require_once().
I can successfully query the db from another file called process.php, but the problem is within a function within that file; it seems my DBO object is out of scope within that function.
Here are the relevant code snippets:
index.php
require_once('./lib/config.php');
config.php
// tested and connects fine
$pdo = new PDO('mysql:host=' . $hostname . ';dbname=' . $dbname, $username, $password, array(
PDO::ATTR_PERSISTENT => true
));
process.php
<?php
...
// can call $pdo fine in this file outside of functions
...
function authenticate($u, $p) {
// can't call $pdo in here, error says $pdo is non-object
$que = $pdo->query('select user_id, user_pass from users where user_name = \'' . $u . '\' limit 1');
...
}
?>
By the way, I'm using PDO because I was having similar trouble with mysqli, and am trying to get away from mysql, which is apparently depreciated and discouraged.
EDIT: I should have clarified first based on the number of responses I got on this matter: I did try to pass $pdo in as a param to the function, with no luck or change in the error message.
SOLUTION: OK, apparently the problem was that I needed to add require_once('config.php') in my process.php file as well. Not sure why (wouldn't it already be included when index.php was run first?). Then I was able to successfully pass $pdo in as a param to my function, and voila.
That's pretty basic PHP stuff. Variables inside functions are local variables unless you use the global keyword to load them. I suppose you want this:
function authenticate(PDO $pdo, $u, $p) {
$que = $pdo->query('select user_id, user_pass from users where user_name = \'' . $u . '\' limit 1');
//...
}
Edit: If PHP claims that $pdo is not an object, it's not an object, so it doesn't really matter how it's passed to the function. Inspect the variable right before you call authenticate():
var_dump($pdo);
Without the relevant code there's no way to say why. (Assuming it's true that new PDO succeeds.)
You need to pass the PDO object as a parameter to the authenticate() function:
function authenticate(PDO $pdo, $u, $p) {
// ..as in the question..
}
Oh and you should be using a place holder for that username in the query, not string concatenation which is prone to SQL injection attacks.
because $pdo has been declared outside of the function authenticate it isn't available inside it. You need to either pass $pdo in
function authenticate($u, $p, $pdo) {
$que = $pdo->query('...');
}
or declare it as global inside the function to be able to access it
function authenticate($u, $p) {
global $pdo;
$que = $pdo->query('...');
}
I need to know how many sql queries are being executed per page request. As the site is already done and I am just running optimization analysis, I would prefer if any solution offered doesnt require that i change the entire website structure.
I use a single connection to send all queries to the MySQL database:
define('DATABASE_SERVER', '127.0.0.1');
define('DATABASE_NAME', 'foco');
define('DATABASE_USERNAME', 'root');
define('DATABASE_PASSWORD', '');
$DB_CONNECTION = new mysqli(
DATABASE_SERVER,
DATABASE_USERNAME,
DATABASE_PASSWORD,
DATABASE_NAME,
3306
);
Then to execute a query i use:
$query = "SELECT * FROM `sometable`";
$queryRun = $DB_CONNECTION->query($query);
Is there a way to count how many queries have been sent and log the answer in a text file just before php closes the connection?
You can extend the mysqli object and override the query method:
class logging_mysqli extends mysqli {
public $count = 0;
public function query($sql) {
$this->count++;
return parent::query($sql);
}
}
$DB_CONNECTION = new logging_mysqli(...);
One of the best ways would be to run a log function inside your $DB_CONNECTION->query().
That way you can either log each individual query to a db table, or perform basic test on query speed and then store this, or just increment the count (for number of queries) and store this.
Create class extending mysqli, make $DB_CONNECTION object of that class and do your statistics in your implementation of query() method. Eventually it shall call parent::query() to do real job.
Create a proxy that you use instead of mysqli directly...
class DatabaseCounter {
private $querycount = 0;
private $mysqli = null;
// create mysqli in here in constructor
public function query(...) {
$this->queryCount++;
$this->mysqli->query(...);
}
}
$DB_CONNECTION = new DatabaseCounter();
I have problem about putting mysql into a function showMsg(). The mysql is working fine if it is not wrapped by function showMsg(), but when I wrap it with function showMsg(), it gives error message "Warning: mysql_query(): supplied argument is not a valid". How to put mysql inside a php function? Below is my codes :
<?php
function showMsg(){
$query2 = "SELECT id, message, username, datetime FROM messageslive ORDER BY id DESC LIMIT 20";
$result2 = mysql_query($query2,$connection) or die (mysql_error());
confirm_query($result2);
$num = mysql_num_rows($result2);
while($msginfo = mysql_fetch_array($result2)){
echo $msginfo['message'];
echo $msginfo['username'];
}
}
<div>
<?php showMsg(); ?>
</div>
?>
Never use global.
Pass $connection into your function as an argument.
Logic and representation should be separated.
Read about MVC: here or here.
Global variables are evil, never use it. If someone suggests it - ignore all their answers.
You probably need:
global $connection;
(Inside the function, that is.)
See Variable Scope
As everyone mentioned, the issue has to do with variable scoping. Instead of add global $connection; you could consider a more OOP approach and consider:
A: passing the $connection variable into the function.
B: placing related functions in a class and pass the DB connection into the Class constructor.
for example:
class YourClass {
private $connection;
public function __construct($connection) {
$this->connection = $connection;
}
public function showMsg(){
$query2 = "SELECT id, message, username, datetime FROM messageslive ORDER BY id DESC LIMIT 20";
$result2 = mysql_query($query2,$this->connection) or die (mysql_error());
confirm_query($result2);
$num = mysql_num_rows($result2);
while($msginfo = mysql_fetch_array($result2)){
echo $msginfo['message'];
echo $msginfo['username'];
}
}
}
I don't have enough rep to comment. But I also like OZ_'s answer :)
$connection variable has no value assigned. The following code should solve your problem (add it at the beginning of the function):
global $connection;
But you should be aware of the fact, that using globals is not a good idea and you may want to:
(preferably) pass $connection variable within the parameter of the function, or
move $connection declaration from outside the function just into the function (if it does not cause additional problems), or
redeclare $connection variable within the function (again: if it will not cause additional problems),
Because variables are local to functions. You need to add this inside your function:
global $connection;
Simply put, functions ignore outside variables due to variable scope. You must let the declare the variable as being from the outside by using global or you can send $connection through a parameter.
I want to be able to call a query function and based on the results they are put into an object that I can call outside the function. This is what I have:
<?php
function query($sql) {
global $r;
$database = "theatre";
$db_conn = pg_connect ("host=localhost port=5432
dbname=$database user=postgres");
if (!$db_conn): ?>
<h1>Failed connecting to postgres database <?php echo $database;?></h1>
<?php
exit;
endif;
$ep = pg_query ($db_conn, $sql);
while ($r = pg_fetch_object ($ep)) {
}
pg_free_result($ep);
pg_close($db_conn);
}
query('select * from test');
echo $r->fname;
I don't want to hardcode any column names into the function. So fname is an example but it will be dynamic based on the query. I have a while loop but not sure what to put in it.
Value returned by function pg_fetch_object is already an object, so no need to loop through results. Just return it:
return pg_fetch_object ($ep);
Then just use the returned results without referring to this awkward global variable $r.
$r = query('select * from test');
echo $r->fname;
Also, no need to free the resource with pg_free_result. It gets freed automatically at end of scope it exists within (that is current function in this case). Calling pg_close may also slow down your script, as the connection will have to be recreated anew next time you call the function. I'd suggest storing connection in local static variable and not closing it at all - it will be closed automatically.
function query($sql) {
$database = "theatre";
static $db_conn;
if (!$db_conn) {
$db_conn = pg_connect ("host=localhost port=5432 dbname=$database user=postgres");
}
...
As a long term solution I'd recommend researching subject of Object-Relational Mapping and learning one of available ORM-ish tools (i.e. Zend Db Table, Doctrine, Propel, or one of existing implementations of ActiveRecord pattern).