Understanding PHP assignments - php

Question

I am having some issues trying to grasp the idea behind certain lines of code that may be above me at this moment since I am fairly sure they have to do with OOP(something that I don't know much about as I am just starting on the concept behind OOP)This came to me as I was readig a PHP book.The code is as follows.
$mysqli = new mysqli('example','example','example');
if(!$mysqli){
die("Could not connect".mysql_error());
}
else {
echo("Connection established");
}
if($mysqli->query("CREATE DATABASE querycreation1")===TRUE){
echo"<p>Database Querycreation1 created</p>";
}
else {
echo "Error creating database".mysql_error();
}
I understand the first couple of lines(and appreciate input on best practices),but the part that I am having issues is after the next set of if-else statements.
The second if statement checks if the creation of a database is true,but can someone explain at what time exactly was the database created? do I need to create one and then check for it in the future? Any input would be greatly appreciated.

Answer 1

In a comparison in PHP first all expressions get evaluated. This means that in
if($mysqli->query("CREATE DATABASE querycreation1")===TRUE)
PHP will first run the query() function on the $mysql-object. That function returns a result. In the case of successfull creating a database it will return TRUE (http://nl1.php.net/mysqli_query). The result of calling this function (TRUE) is then compared to TRUE.
Perhaps more verbose for you to see this:
$databaseCreated = $mysqli->query("CREATE DATABASE querycreation1");
if($databaseCreated ===TRUE){
echo"<p>Database Querycreation1 created</p>";
}
else {
echo "Error creating database".mysql_error();
}

Answer 2

$mysqli->query() performs the query, in this case, a CREATE query. The function then returns TRUE if the query was executed successfully and FALSE if an error occurred. So the database is created exactly at the time the first argument to the === comparison is evaluated.
Generally, creating databases in php scripts won't happen often, usually only in "installation" scripts use to setup some php driven piece of software (such as a discussion board/forum). Other than that, you'll want to create the databases once either through a database management system such as phpMyAdmin or a script you delete afterwards. Then in your actual site scripts, you just assume the databases exist because you also usually don't just delete them.
You could write it differently by assigning the return value of the query to a variable and checking against that:
$success = $mysqli->query("CREATE DATABASE querycreation1");
if ($success===TRUE){
// ...
But that's purely a matter of preference.
Also, the first else is not strictly necessary because of the die statement. There is a number of ways you could simplify (or let's say modify) that part:
// The "just no else" version
if (!$mysqli)
die("Could not connect".mysql_error());
echo("Connection established");
// The one-liner version
if (!$mysqli) die("Could not connect".mysql_error());
echo("Connection established");
// The short-circuit version
$mysqli OR die("Could not connect".mysql_error());
echo("Connection established");
// same using the symbolic version of OR
$mysqli || die("Could not connect".mysql_error());
echo("Connection established");
// you can also include that in the first call
$mysqli = new mysqli('example','example','example') OR die("Could not connect".mysql_error());
echo("Connection established");
The last three examples work based on the fact that php handles logical operators in a short-circuit way, that is, if the first part is TRUE, then the entire OR expression will be TRUE no matter what the second argument is, so php doesn't even bother evaluating it. If the first part is FALSE, however, the expression's value depends on the second argument, so it is evaluated.

Answer 3

Point one:
You are creating an instance of a class mysqli which contains methods to connect, query, manage database. You need to pass some parameters which are used by the class'es constructor to connect to the database.
This instance is called an object and now this object has the connection and can use the methods from the class to query, manage that database.
For better understanding: http://www.php.net/manual/en/language.oop5.php