Problem when trying to query with PHP and MYSQL

Question

I’m trying to make a query directly in the PHP file where it creates the connection to the database. This query will create my table. The problem is that I am trying to reference the connection variable in mysqli_query() and it’s not being referenced (I believe this is the problem). I did it in this structure because I’m doing Object-Oriented!

The mistake you’re making is: Warning: mysqli_query() expects Parameter 1 to be mysqli, Boolean Given in...

Follows the code:

<?php

class db{

    private $dbServer = "localhost";
    private $dbUser = "root";
    private $dbPassword = "";
    private $dbName = "sql_queries";
    private $conn;

    public function __construct(){
        $this->conn = mysqli_connect($this->dbServer, $this->dbUser, $this->dbPassword) or die("Não foi possível estabelecer a conexão com a base de dados! ".mysqli_error($this->conn));
        $this->conn = mysqli_select_db($this->conn, $this->dbName) or die("Não foi possível se conectar com o banco de dados! ".mysqli_error($this->conn));

        $this->setQuery();
    }

    public function getConn(){
        return $this->conn;
    }

    public function setQuery(){

        $sql = "CREATE TABLE IF NOT EXISTS sql_queries.aluno(
            aluno_id INT NOT NULL AUTO_INCREMENT,
            nome_aluno varchar(255),
            dataNascimento_aluno date,
            nome_pai varchar(255),
            nome_mae varchar(255),
            RG_aluno char(10),
            cpf_aluno char(11),
            telefone_aluno char(10),
            celular_aluno char(13),
            CONSTRAINT PK_aluno PRIMARY KEY (aluno_id)
            );";

            $result = mysqli_query($this->conn, $sql);
    }
}

Answer 1

The problem is you set twice the $this->conn:

$this->conn = mysqli_connect($this->dbServer, $this->dbUser, $this->dbPassword) or die("Não foi possível estabelecer a conexão com a base de dados! ".mysqli_error($this->conn));
$this->conn = mysqli_select_db($this->conn, $this->dbName) or die("Não foi possível se conectar com o banco de dados! ".mysqli_error($this->conn));

Should be:

$this->conn = mysqli_connect($this->dbServer, $this->dbUser, $this->dbPassword) or die("Não foi possível estabelecer a conexão com a base de dados! ".mysqli_error($this->conn));
mysqli_select_db($this->conn, $this->dbName) or die("Não foi possível se conectar com o banco de dados! ".mysqli_error($this->conn));

For the $this->conn must be the result of mysqli_connect, because it will contain the "link", the function mysqli_select_db It’s just to change banks, actually you don’t even need it, just if you want to change banks during the run, you can simplify to this:

public function __construct(){
    $this->conn = mysqli_connect($this->dbServer, $this->dbUser, $this->dbPassword, $this->dbName) or die("Não foi possível estabelecer a conexão com a base de dados! ".mysqli_error($this->conn));

    $this->setQuery();
}