Dynamically create PHP object based on string

Question

I would like to create an object in PHP based on a type defined by a string in a MySQL database. The database table has columns and sample data of:

 id | type | propertyVal ----+------+-------------   1 | foo  | lorum   2 | bar  | ipsum 

...with PHP data types

class ParentClass {...} class Foo extends ParentClass {private $id, $propertyVal; ...} class Bar extends ParentClass {private $id, $propertyVal; ...}  //...(more classes)... 

Using only one query, I would like to SELECT a row by id and create an object of the type define the table's type column with other columns in the SELECTed row being assigned to the newly created object.

I was thinking that using:

1. mysql_fetch_object()
2. Reading the type attribute
3. Creating an object with type defined by type attribute

But know of no way to dynamically create a type based on a string. How does one do this?

Answer 1

But know of no way to dynamically create a type based on a string. How does one do this?

You can do it quite easily and naturally:

$type = 'myclass';  $instance = new $type; 

If your query is returning an associative array, you can assign properties using similar syntax:

// build object $type = $row['type']; $instance = new $type;  // remove 'type' so we don't set $instance->type = 'foo' or 'bar' unset($row['type']);    // assign properties foreach ($row as $property => $value) {    $instance->$property = $value; } 

Answer 2

There's a very neat syntax you can use that I learned about a couple of months ago that does not rely on a temporary variable. Here's an example where I use a POST variable to load a specific class:

$eb = new ${!${''} = $_POST['entity'] . 'Binding'}(); 

In your specific case though, you would be able to solve it by using PDO. It has a fetch mode that allows the first column's value to be the class the row instantiates into.

$sth->fetch(PDO::FETCH_CLASS | PDO::FETCH_CLASSTYPE);