is that nested methods right? why I get empty query? - php

Question

I wonder why I get errors with that code? Can Someone help?
My class is to get some information from database using nested methods,suppose I get an empty query
<?php
class db {
public function __construct(){
if(mysql_connect("localhost","root","0000")){
mysql_select_db("myblog");
}else{
echo mysql_error();
}
}
public function select($row){
$sql="SELECT".$row;
return $this;
}
public function from($table){
$sql.="FROM".$table;
return $this;
}
public function where($condition){
$sql.="WHERE".$condition;
return $this;
}
}
$ddb=new db;
$qq=$ddb->select("*")->from("news")->where("id='1'");
$query= mysql_query($qq);
while($row=mysql_fetch_object($query)){
echo $row->title;
}
?>

Answer 1

You have to define __toString() special method to use your object as a string:
class db {
private $sql = '';
public function __construct() {
if (mysql_connect("localhost", "root", "0000")) {
mysql_select_db("myblog");
} else {
echo mysql_error();
}
}
public function select($row) {
$this->sql = "SELECT ".$row;
return $this;
}
public function from($table) {
$this->sql .= " FROM ".$table;
return $this;
}
public function where($condition) {
$this->sql .= " WHERE ".$condition;
return $this;
}
public function __toString() {
return $this->sql;
}
}
$ddb = new db();
$qq = $ddb->select("*")->from("news")->where("id='1'");
$query = mysql_query($qq);
while ($row = mysql_fetch_object($query)) {
echo $row->title;
}

Answer 2

You need to be using $this in each of the methods to append to $sql
// Declare the class property
public $sql = "";
// And use $this->sql in the methods
// Also note whitespace added around SELECT, FROM, WHERE
public function select($row){
$this->sql="SELECT ".$row;
return $this;
}
public function from($table){
$this->sql.=" FROM ".$table;
return $this;
}
public function where($condition){
$this->sql.=" WHERE ".$condition;
return $this;
}
Then when you query it, use $ddb->sql, since you are not returning the SQL string.
$ddb->select("*")->from("news")->where("id='1'");
$query = mysql_query($ddb->sql);
And it goes without saying that hopefully you intend to be calling mysql_real_escape_string() on any variables you construct into your where() method. As it is, you have no particular escaping on it.

Answer 3

run a var_dump on $qq
That will show you the problem instantly.
To me it looks as if you are missing a couple of spaces in your query and that you aren't returning the query string $sql but instead $this in your db class

Answer 4

use $this->sql instead of $sql in the methods select, from, where
output the query like this: $ddb->select("*")->from("news")->where("id='1'")->sql or create a getSQL() method which just returns the $sql field and query it like $ddb->select("*")->from("news")->where("id='1'")->getSQL()
You should also consider creating a method which creates a mysql_query (not just the string) or some methods for retrieving methods, so it's easier to use.