php, how to connect to a database as a class, send sql statments and return the result

Question

Forgive me if the question is a little odd
I can clarify if needed:

I have the code that can connect to a mysql database as normal, however i have encapsulated it as a class:

<?php
define("HOST", "127.0.0.1");     // The host you want to connect to.
define("USER", "phpuser");    // The database username.
define("PASSWORD", "Secretpassword");    // The database password.

class DBConnection{

    function conn($sql, $database){
        $DB = new mysqli(HOST,USER,PASSWORD,$database);
        if ($DB->connect_error){
            die("Connection failed: " . $DB->connect_error);
            exit();
        }

        if ($result = $DB->query($sql)){
            return TRUE;
            $DB->close();
         } 
         else{            
             echo "Error: " . $sql . "<br>" . $DB->error;            
             $DB->close();
         }
    }
}
?>

I have done it this way so i can include this class in any subsequent php page and allow them to send it an sql statment and the database, see below as an example:

$sql = ("INSERT INTO  users (first_name, last_name, username, email, password, group_level) VALUES ('John', 'Doah','JDoah', 'example@email', 'password', 'user')");

        $DB = new DBConnection;
        $result = $DB->conn($sql,"members");

        if ($result ==TRUE){
            return "Record added sucessfully";
        }

This works fine. however, im looking to send other sql statments to DBConnection.

How do i do that and to have it pass back any results that it recives? errors, boolean, row data etc. The caller will worry about parsing it.

Hopefully that makes sense.

Answer 1

This is an old class I used to use way back in the days of mysql still works but will need to be updated for mysqli or newer

class DBManager{
    private $credentials = array(
        "host" => "localhost",
        "user" => "",
        "pass" => "",
        "db" => ""
    );

    function DBManager(){
        $this->ConnectToDBServer();
    }

    function ConnectToDBServer(){
        mysql_connect($this->credentials["host"],$this->credentials["user"],$this->credentials["pass"]) or die(mysql_error());
        $this->ConnectToDB();
        session_start();
    }

    function ConnectToDB(){
        mysql_select_db($this->credentials["db"]) or die(mysql_error());
    }

    function Insert($tableName,$data){
        $parameters = '';

        $len = count($data);
        $i = 0;
        foreach($data as $key => $value){
            if(++$i === $len){
                $parameters .= $key . "='$value'";
            }else{
                $parameters .= $key . "='$value'" . ", ";
            }
        }

        $query = "INSERT INTO $tableName SET $parameters";

        mysql_query($query) or die(mysql_error());
        return true;
    }

    function GetRow($tableName,$select,$where){
        $selection = '';

        $len = count($select);
        $i = 0;
        foreach($select as $key){
            if(++$i === $len){
                $selection .= $key;
            }else{
                $selection .= $key . ",";
            }
        }

        $whereAt = '';

        foreach($where as $key => $value){
            $whereAt .= $key . "='$value'";
        }

        $query = "SELECT $selection FROM $tableName WHERE $whereAt";
        $result = mysql_query($query);

        while($row = mysql_fetch_array($result)){
            return $row;
        }
    }
}

The key things here is you can create a persistent connection to your database without rewriting a bunch of code

Example

global $DB;
$DB = new DBManager();

Since the connection happens in the constructor you will now have a connection on the page you call this code and can begin getting and setting to the database through use of $DB->GetRow() and $DB->Insert() which makes things much easier and was modeled after the $wpdb instance which is a class that manages the database in wordpress sites

Examples

For these examples we will assume you have a table as such

Insert new student

//create an associative array
$data = array(
  "student_id" => 1,
  "birth_date" => "02/06/1992",
  "grade_level" => 4
);

//Send Call

$dm->Insert("student",$data);

Get data

//Create selection
$selection = array("grade_level");

//Create associative array for where we want to find the data at
$where = array(
"id" => 1
);

//Get Result
$result = $dm->GetRow("student",$selection,$where);

//do something with result
echo $result->grade_level;