Chaining methods in PHP - php

Question

$db->select("users")->where(array("username", "=", "username"));
$db->update("users", array("username" => "username", "password" => "12345"))->where(array("id", "=", "14"));
Ok, I want to write the statements like above, by chain the where() method onto select, update and delete.
My problem is; how to determine if I used the select, update or delete before the where, so I can bind the right values onto the right statement.
I want something like this:
public function where() {
if($this->select()) {
// so if $db->select("users")->where(array("username", "=", "username"));
// save the where data in the select variable.
}
elseif($this->update()) {
// so if $db->update("users", array("username" => "username", "password" => "12345"))->where(array("id", "=", "14"));
// save the where data in the update variable.
}
elseif($this->delete()) {
// so if $db->delete("users")->where(array("username", "=", "username"));
// save the where data in the delete variable.
}
}
But the code above is of course not valid, and I dont use any frameworks.
public function select($table, $what = null) {
$what == null ? $what = "*" : $what;
$this->_select = "SELECT {$what} FROM {$table}";
return $this;
}

Answer 1

You would have to maintain that state. It's not about telling whether the previous call was a select() or an update(), that's the wrong way to think about the problem. You just need each of select/update/delete to modify $this, so that $this, always knows what kind of query it's building.
A dead simple example:
public function select() {
$this->kind == 'select';
return $this;
}
public function where() {
if ($this->kind == 'select') {
...
return $this;
}
The only thing that your chained methods share is that they each return $this, so that a subsequent method can be chained onto the end. It's all about storing up state in $this until some final method call actually evalates the built-up query.

Answer 2

Something like:
public function select($table, $fields = '*')
{
$this->query = "SELECT {$fields} FROM `{$table}`";
return $this;
}
public function where($conditions = [])
{
if ($this->query)
{
if ($conditions)
{
foreach ($conditions as $key => &$val)
$val = "`{$key}` = '{$val}'";
$this->query .= ' WHERE ' . implode(' AND ', $conditions);
}
$db->query($this->query);
$this->query = '';
return $this;
}
}
This would work, however, you have to notice that this structure would allow you to do things like:
$db->where();
This is perfectly valid even though doesn't make sence to call where() in the database directly.
Also, queries that don't require a WHERE clause would not run, because only where() actually makes the call.
How to solve this?
We can actually use a very interesting mechanic of OOP: The destructor method. PHP destroys objects immediately after they are no longer in use, and we can explore this feature here as a trigger to run the query. We only have to separate the query to a new object.
class dbQuery
{
private $db;
private $conditions = [];
function where($conditions = [])
{
$this->conditions = array_merge($this->conditions, $conditions);
return $this;
}
function __construct($db, $query)
{
$this->db = $db;
$this->query = $query;
}
function __destruct()
{
if ($this->conditions)
{
foreach ($this->conditions as $key => &$val)
$val = "`{$key}` = '{$val}'";
$this->query .= ' WHERE ' . implode(' AND ', $this->conditions);
}
$this->db->result = $db->query($this->query);
}
}
class Database
{
public $result = null;
protected static $instance;
function __construct()
{
if (!self::$instance)
self::$instance = new mysqli('localhost', 'user', 'password', 'dbname');
}
public function query($query)
{
return self::$instance->query($query);
}
public function select($table, $fields = '*')
{
return new dbQuery($this, "SELECT {$fields} FROM `{$table}`");
}
}
This way $db->where() won't work as it doesnt exist, and using $db->select('table') or $db->select('table')->where([...]) will both give results, and even allows extending the syntax to use where() multiple times like:
$db->select('table')->where(['id' => 100])->where(['price' => 1.99]);