selective/transformer

A strictly typed array transformer with dot access and fluent interface. The mapped result can be used for JSON responses and many other things.

Table of Contents

• Requirements
• Installation
• Introduction
• Dot access
  • Object access
• Transforming
  • Transforming list of arrays
• Mapping rules
  • Simple mapping rules
  • Complex mapping rules
• Filter
  • Custom Filter
• Examples
  • JSON conversion
  • PDO resultset conversion
• License

Requirements

• PHP 7.2+ or 8.0+

Installation

composer require selective/transformer

Introduction

This Transformer component provides functionality to map, cast and loop array values from an array or object to another array.

Converting complex data with simple PHP works by using a lot of type casting, if conditions and looping through the data with foreach(). This leads to very high cyclomatic complexity and nesting depth, and thus poor "code rating".

Before: Conditions: 9, Paths: 256, CRAP Score: 9

Click to expand!

After: Conditions: 1, Paths: 1, CRAP Score: 1

Click to expand!

Use Cases

When building an API it is common for people to just grab stuff from the database and pass it to json_encode(). This might be passable for “trivial” APIs but if they are in use by the public, or used by mobile applications then this will quickly lead to inconsistent output. The Transformer is able to create a “barrier” between source data and output, so schema changes do not affect users.

The Transformer works also very well to put any kind of database resultset (e.g. from PDO) into a new data structure.

The uses cases are not limited.

Dot access

You can copy any data from the source array to any sub-element of the destination array using the dot-syntax.

<?php
use Selective\Transformer\ArrayTransformer;

$transformer = new ArrayTransformer();

$transformer->map('firstName', 'address.first_name')
    ->map('lastName', 'address.last_name')
    ->map('invoice.items', 'root.sub1.sub2.items');

// ...

Object access

It's possible to access the properties of an object using the dot notation.

use Selective\Transformer\ArrayTransformer;

$transformer = new ArrayTransformer();

$transformer->map('bar1', 'foo.bar', 'string')
    ->map('bar2', 'foo.bar2.0', 'string')
    ->map('sub.sub2.sub3', 'foo.bar2.1', 'string');

$user = new stdClass();
$user->foo = new stdClass();
$user->foo->bar = 'Hello Bar';
$user->foo->bar2 = [
    0 => 'Test 0',
    1 => 'Test 1',
];

$result = $transformer->toArray((array)$user);

The result:

[
    'bar1' => 'Hello Bar',
    'bar2' => 'Test 0',
    'sub' => [
        'sub2' => [
            'sub3' => 'Test 1',
        ],
    ],
];

Transforming

Transforming arrays

For the sake of simplicity, this example has been put together as though it was one file. In reality, you would spread the manager initiation, data collection and JSON conversion into separate parts of your application.

Sample data:

$data = [
    'first_name' => 'Sally',
    'last_name' => '',
    'email' => '[email protected]',
];

<?php

use Selective\Transformer\ArrayTransformer;

$transformer = new ArrayTransformer();

$transformer->map('firstName', 'first_name')
    ->map('lastName', 'last_name')
    ->map('email', 'email');
    
$result = $transformer->toArray($data);

The result:

[
    'firstName' => 'Sally',
    'email' => '[email protected]',
];

Transforming list of arrays

The method toArrays is able to transform a list of arrays.

This can be useful if you want to transform a resultset from a database query, or a response payload from an API.

Example:

$transformer = new ArrayTransformer();

$transformer->map('id', 'id', $transformer->rule()->integer())
    ->map('first_name', 'first_name', $transformer->rule()->string())
    ->map('last_name', 'last_name', $transformer->rule()->string())
    ->map('phone', 'phone', $transformer->rule()->string())
    ->map('enabled', 'enabled', $transformer->rule()->boolean());

$rows = [];
$rows[] = [
    'id' => '100',
    'first_name' => 'Sally',
    'last_name' => '',
    'phone' => null,
    'enabled' => '1',
];

$rows[] = [
    'id' => '101',
    'first_name' => 'Max',
    'last_name' => 'Doe',
    'phone' => '+123456789',
    'enabled' => '0',
];

$result = $transformer->toArrays($rows);

The result:

[
    [
        'id' => 100,
        'first_name' => 'Sally',
        'enabled' => true,
    ],
    [
        'id' => 101,
        'first_name' => 'Max',
        'last_name' => 'Doe',
        'phone' => '+123456789',
        'enabled' => false,
    ],
]

Mapping Rules

Simple mapping rules

Using strings, separated by |, to define a filter chain:

<?php

use Selective\Transformer\ArrayTransformer;

$transformer = new ArrayTransformer();

$transformer->map('firstName', 'first_name', 'string|required')
    ->map('lastName', 'last_name', 'string|required')
    ->map('email', 'email', 'string|required');

$data = [
    'first_name' => 'Sally',
    'last_name' => '',
    'email' => '[email protected]',
];
    
$result = $transformer->toArray($data);

Because lastName is blank but required the result looks like this:

[
    'firstName' => 'Sally',
    'lastName' => '',
    'email' => '[email protected]',
];

Complex mapping rules

For complexer mapping rules there is a fluent interface available. To create a new rule use the rule method and pass it as 3rd. parameter to the map method.

<?php

use Selective\Transformer\ArrayTransformer;

$transformer = new ArrayTransformer();

$transformer->map('firstName', 'first_name', $transformer->rule()->string()->required())
    ->map('lastName', 'last_name', $transformer->rule()->string()->required())
    ->map('email', 'email', $transformer->rule()->string()->required());

$data = [
    'first_name' => 'Sally',
    'last_name' => '',
    'email' => '[email protected]',
];

$result = $transformer->toArray($data);

Because lastName is blank but required the result looks like this:

[
    'firstName' => 'Sally',
    'lastName' => '',
    'email' => '[email protected]',
];

Filter

Most filters are directly available as method.

// Cast value to string, convert blank to null
$transformer->rule()->string();

// Cast value to string, allow blank string ''
$transformer->rule()->string(true);

// Cast value to int
$transformer->rule()->integer();

// Cast value to float
$transformer->rule()->float();

// Cast value to bool
$transformer->rule()->boolean();

// Cast value to datetime string, default: Y-m-d H:i:s
$transformer->rule()->date();

// Cast value to date string
$transformer->rule()->date('Y-m-d');

// Format value to number using the number_format function
$transformer->rule()->number();

// Format value to number with a custom number format
$transformer->rule()->number(2, '.', ',');

// Cast value to array
$transformer->rule()->array();

// Cast value using a custom callback function
$transformer->rule()->callback(
    function ($value) {
        return 'My custom value: ' . $value;
    }
);

// Set fixed value
$transformer->set('bar.0.item', 'default-value');

// Apply transformation to array item
$transformer->rule()->transform(
    function (ArrayTransformer $transformer) {
        $transformer
            ->map('id', 'id', 'integer')
            ->map('first_name', 'first_name', 'string');
    }
);

// Apply transformation to a list of arrays
$transformer->rule()->transformList(
    function (ArrayTransformer $transformer) {
        $transformer
            ->map('id', 'id', 'integer')
            ->map('first_name', 'first_name', 'string');
       }
);

Custom Filter

You can also add your own custom filter:

$transformer = new ArrayTransformer();

// Add a trim filter using the native trim function
$transformer->registerFilter('trim', 'trim');

// Usage
$transformer->map('destination', 'source', 'trim');

// or

$transformer->map('destination', 'source', $transformer->rule()->filter('trim'));

Add a custom filter using a callback:

$transformer = new ArrayTransformer();

$transformer->registerFilter(
    'custom1',
    function ($value) {
        return 'Custom value: ' . $value;
    }
);

// Usage
$transformer->map('destination', 'source', 'custom1');

// or

$transformer->map('destination', 'source', $transformer->rule()->filter('custom1'));

// It is possible to chain multiple filters
$transformer->map(
    'destination',
    'source',
    $transformer->rule()->filter('custom1')->filter('trim')->required()->default('example')
);

Define a custom filter using a mapping specific callback:

$transformer = new ArrayTransformer();

$transformer->map(
    'destination',
    'source',
    $transformer->rule()->callback(
        function ($value) {
            return 'Callback value: ' . $value;
        }
    )
);

There are even more filter classes available that can be registered manually:

use Selective\Transformer\Filter;

$transformer = new ArrayTransformer();

// Convert the value using the sprintf function
$transformer->registerFilter('sprintf', SprintfFilter::class);

// Usage
$transformer->map('destination', 'source', $transformer->rule()->filter('sprintf', 'Count: %d'));

You can also implement and register your own filter classes as well.

Examples

JSON conversion

You can use your own json component or just the native json_encode function.

// Turn all of that into a JSON string
$json = (string)json_encode($transformer->toArray($data));

Writing JSON to a PSR-7 response object:

// Set correct header
$response = $response->withHeader('Content-Type', 'application/json');

// Write json string to the response body
$response->getBody()->write($json);

return $response;

PDO resultset conversion

use Selective\Transformer\ArrayTransformer;

$pdo = new PDO($dsn, $username, $password, $options);

$statement = $pdo->query('SELECT id, username, first_name FROM users');
$rows = $statement->fetchAll();

$transformer = new ArrayTransformer();

$transformer->map('id', 'id', 'integer')
    ->map('username', 'username', 'string|required')
    ->map('first_name', 'first_name', 'string|required');
    
$result = $transformer->toArrays($rows);

The result:

[
    [
        'id' => 1,
        'username' => 'sally',
        'first_name' => 'Sally',
    ]  
    // ... 
];

License

The MIT License (MIT). Please see License File for more information.