UUID instead of an auto-increment integer for ID with Active Record

I have a dream ... I am happy to join with you today in what will go down in history as the greatest demonstration of bad design of Active Record.

I have an API. It's built with a RESTful extension over Active Record, and some endpoints provide PUT methods to upload files. By a REST design we create an entity with POST /video first, and then upload a video file with PUT /video/{id}/data.

How do we get the {id}? The essential solutuion is UUID generated by a client. It allows API application to be stateless and scale it, use master-master replication for databases and feel yourself a modern guy. If you have Postgres — lucky you, feel free to use the built-in UUID data type and close this article. With MySQL the essential solution is insert into users values(unhex(replace(uuid(),'-',''))... MySQL team recommends updating our INSERT queries. With Active Record it is not really possible. For fetching UUIDs it recommends adding a virtual column — this can be used.

If you design the application from ground up, you can use defferent fields for a binary and text representation of UUID, and reference them in different parts of an application, but I am bound to the legacy code.

Adding getId()/setId() won't help - data comes from a client in JSON and fills the model object with a setAttributes() call avoiding generic magic methods.

Here's the hack:

Step 1. Add a private $idText property

use yii\db\ActiveRecord;
class Video extends ActiveRecord
{
    private $idText;

Step 2. Add two validators and a filter

//check if value is a valid UUID
['id','match', 'pattern'=>'/^[0-9a-f]{8}-[0-9a-f]{4}-[1-5][0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$/i'],
// convert UUID from text value to binary and store the text value in a private variable,
// this is a workaround for lack of mapping in active record
['id','filter','skipOnError' => true, 'filter' => function($uuid) {
    $this->idText = $uuid;
    return pack("H*", str_replace('-', '', $uuid));
}],
//now let's check if ID is taken
['id','unique','filter' => function(\yii\db\Query $q) {
    $q->where(['id' => $this->getAttribute('id')]);
}],

First rule is a validator for an input. Second rule is a filter preparing UUID to be written in a binary format and keeping the text form for output. Third one is a validator running a query over the binary value generated by a filter.

Note: I wrote $this->getAttribute('id'), $this->id returns a text form.

We can write a query to validate data, not to save it.

Step 3. Add getters

public function __get($name)
{
    return ($name === 'id') ? $this->getId() : parent::__get($name);
}

/**
 * Return UUID in a textual representation
 */
public function getId(): string
{
    if ($this->idText === NULL && $this->getIsNewRecord()){
        //the filter did not convert ID to binary yet, return the data from input
        return strtoupper($this->getAttribute('id'));
    }
    //ID is converted
    return strtoupper($this->idText ?? $this->getAttribute('id_text'));
}

When we call the $model->id property we need the getId() executed. But Active Record base class overrides Yii compoent default behavior and does not call a getter method of an object if a property is a field in a table. So I override the magic getter. From the other hand, a regexp valiator I wrote calls $model->id, triggering the getter before the UUID is saved to the private property. I check if the object is newly created to serve the text value for validator.

Note the strtoupper() call: client may send UUID in both upper and low cases, but after unpacking from binary we will have a value in upper case. I received different string values before storing data to DB and after fetching it. Convert the textual UUID value to an upper or lower case everywhere to avoid problems.

It looks weird to mutate data in a validator, but I found this is the best way. I belive I shouldn't use beforeSave() callback to set the binary value for generating SQL, and return the text value back in afterSave() - supporting this code would be a classic hell like #define true false;.

Step 4. Define the mapping for output

public function fields()
{
    $fields = parent::fields();
    $fields['id'] =function(){return $this->getId();};
    return $fields;
}

This method is used by RESTful serializers to format data when you access your API with GET /video requests.

So, now you can go the generic MySQL way

Step 5. add a virtual column

ALTER TABLE t1 ADD id_text varchar(36) generated always as
 (insert(
    insert(
      insert(
        insert(hex(id_bin),9,0,'-'),
        14,0,'-'),
      19,0,'-'),
    24,0,'-')
 ) virtual;

Step 5. Use Object Relation Mapping in Yii 3 when it's available and write mapping instead of these hacks.

P.S. A couple of helper functions.

declare(strict_types=1);

namespace common\helpers;


class UUIDHelper
{
    const UUID_REGEXP = '/^[0-9a-f]{8}-[0-9a-f]{4}-[1-5][0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$/i';

    public static function string2bin(string $uuid): string
    {
        return pack("H*", str_replace('-', '', $uuid));
    }

    public static function bin2string(string $binary): string
    {
        return strtolower(join("-", unpack("H8time_low/H4time_mid/H4time_hi/H4clock_seq_hi/H12clock_seq_low", $binary)));
    }

    public static function isUUID(string $uuid): bool
    {
        return (bool)preg_match(self::UUID_REGEXP,$uuid);
    }
}
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Viewed: 22 225 times
Version: 2.0
Category: How-tos
Written by: grigori
Last updated by: samdark
Created on: Nov 25, 2019
Last updated: 7 months ago
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