试图让一个类的函数在另一个函数内部工作是不成功的

Question

I'm trying to get a function inside of a class to work with another function with no success.

Here is my code:

<?php
class db {

    public function dbLogin() {
        $mysqli = new mysqli("127.0.0.1","user","passowrd","database");

        if ($mysqli->connect_errno) {
        echo "Failed to connect to MySQL: (" . $mysqli->connect_errno . ") " . $mysqli->connect_error;
        }
        echo $mysqli->host_info . "
";
    }

    public function selectQuery() {
        $this->dbLogin();
        $query = "
            SELECT      column
            FROM        table
        ";

        if ($mysqli->query($query)) {
            echo "success";
        }       
    }
}

$fData = new db();
$fData->dbLogin();
$fData->selectQuery();
?>

The database connection works fine. I cannot get anything to echo once the query line runs, though.

What I've tried so far:

-Replacing the dbLogin() function with a construct() function, then getting rid of the $this->dbLogin line and $fData->dbLogin() line. This did not work.

-Moving this code around in different variations, just in case my order was wrong. That did nothing.

-Googling/looking at similar questions on StackOverflow with no luck.

I can do this procedural style easily, but it's time for me to move away from that. I am sure that there are much better ways to connect to a database using an OOP design pattern, but I am brand new to OOP so I am trying to use this as a lesson, and to gain a better understanding as to how functions interact with each other inside of a class. I know that I can throw the connection and query in one function, but then I would not know how to make functions interact with one another inside of a class.

How do I run the query in the selectQuery function based on the login information in the dbLogin function?

Answer 1

You need to define your $mysqli outside the function, the problem with your code is related to global and local scope.

 <?php
 class db {
private $mysqli;
public function dbLogin() {
        $this->mysqli = new       mysqli("127.0.0.1","user","passowrd","database");

    if ($this->mysqli->connect_errno) {
    echo "Failed to connect to MySQL: (" . $this->mysqli->connect_errno . ") " . $mysqli->connect_error;
    }
    echo $mysqli->host_info . "
";
}

public function selectQuery() {
    $this->dbLogin();
    $query = "
        SELECT      column
        FROM        table
    ";

    if ($this->mysqli->query($query)) {
        echo "success";
    }       
}
}

$fData = new db();
$fData->dbLogin();
$fData->selectQuery();
?>

this will work