beatswitch/distil

0.2.0 2019-11-05 14:42 UTC

This package is auto-updated.

Last update: 2022-04-19 14:07:47 UTC


README

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Distil provides a simple API to describe a variable number of conditions that should be met by a result set in PHP. This, for example, makes dynamically constructing queries through small value objects a breeze.

Getting Started

Simple Example

Let's consider the following scenario: you have a query object GetPosts that returns all posts of your blog by default. However, you only need to retrieve posts from a specific author on some places. The query itself is identical, you only need to strip out the ones that were created by anyone other than the given author. To do so, the query object can accept criteria that may or may not hold the "author" criterion:

$authorId = 369;

// Author is an implementation of Distil\Criterion which acts as a Criteria factory.
$criteria = Author::criteria($authorId);

$posts = $getPostsQuery->get($criteria);

The query object internals can then append statements to the query depending of the given criteria. Distil only describes the criteria, you can interpret them however you want. You're fully in control:

use Distil\Criteria;

final class GetPosts
{
    public function get(Criteria $criteria)
    {
        ...
        
        if ($criteria->has('author')) {
            $query->where('creator_id', '=', $criteria->get('author')->value());
        }
    }
}

This approach comes in handy when you need to pass along a variable number of criteria to a single query. Imagine we'd use that GetPosts query object to expose those posts through an API and allow users to filter them by author, publish_date, ... and eventually sort them differently:

$criteria = new Distil\Criteria();

if (isset($requestData['author'])) {
    $criteria->add(Author::fromString($requestData['author']));
}

if (isset($requestData['sort'])) {
    $criteria->add(new Sort($requestData['sort']));
}

...

$posts = $getPostsQuery->get($criteria);

Requirements

  • PHP >= 7.1

Installation

You can install this package through Composer:

$ composer require remipelhate/distil

Concepts

Criteria

Criteria is a collection of conditionals that describe which records should be included within a result set (filtering, limiting, ...) or how it should be presented (e.g. sorting). Distil represents these single conditionals within the Distil\Criteria collection as Distil\Criterion instances (see next chapter).

Adding Criteria

Let's reconsider the example at the top of the docs. Imagine we'd want to retrieve all posts from author with ID 1 and sort them in ascending order of the publish_date. You can pass along Criterion instances on construction:

$criteria = new Distil\Criteria(new Author($authorId), new Sort('publish_date'));

… or fluently through the add() method:

$criteria = new Distil\Criteria();

$criteria->add(new Author($authorId))
    ->add(new Sort('publish_date'));

Each Criterion instance within the collection is unique by name. add() does not allow to overwrite an instance in the collection with another one carrying the same name. If you event need to overwrite one, you can use the set() method:

$criteria = new Distil\Criteria(new Author(1));

$criteria->add(new Author(2)); // This will throw an Exception.
$criteria->set(new Author(2)); // This will overwrite new Author(1) with new Author(2)

Getting Criteria

You can check if it contains a Criterion instance by name:

$criteria = new Distil\Criteria(new Author(1));

$criteria->has('published'); // returns false
$criteria->has('author'); // returns true

... and get it:

$criteria = new Distil\Criteria(new Author(1));

$criteria->get('published'); // returns null
$criteria->get('author'); // returns the Author instance

Array Access

Distil\Criteria implements PHP's ArrayAccess interface, meaning you can interact with it as an array:

$criteria[] = new Author(1); // Acts as set()
$author = $criteria['author']; // Acts as get(), but throws an error if the name doesn't exist

Criterion

A Criterion is a single condition to which a result set should adhere. Think of a filter, a limit, sorting, ... Distil represents these as small value objects (identified by a unique name) that wrap around a single value. Those objects must implement the Distil\Criterion interface.

Example

Once more, let's go back to our example at the top of the docs and create that author filter for the query object. This filter holds the ID of an author:

use Distil\Criterion;

final class Author implements Criterion
{
    const NAME = 'author';

    public function __construct(int $id)
    {
        $this->id = $id;    
    }
    
    public function name(): string
    {
        return self::NAME;
    }
    
    public function value(): int
    {
        return $this->id;
    }
}

Typed Criteria

Distil ships with a set of strictly typed abstract classes that you can use to add some default behaviour to your Criterion implementations:

  • Distil\Types\BooleanCriterion - Wraps around a boolean value.
  • Distil\Types\DateTimeCriterion - Wraps around an instance of PHP's DateTimeInterface and optionally accepts a datetime format.
  • Distil\Types\IntegerCriterion - Wraps around a integer value.
  • Distil\Types\ListCriterion - Wraps around an array value.
  • Distil\Types\StringCriterion - Wraps around a string value.

Each of these can:

  • be constructed from a string value through the fromString named constructor (remember, the default constructor of these are all strictly typed). This is particularly useful when instantiating Criterion instances from a URI query string value.
  • be constructed from string keywords (see Keywords).
  • be casted to a string.
  • act as a Distil\Criteria factory (see Criteria Factories).

So, we can simplify our Author filter from above as such:

use Distil\Types\IntegerCriterion;

final class Author extends IntegerCriterion
{
    const NAME = 'author';
    
    public function name(): string
    {
        return self::NAME;
    }
}

Keywords

When creating a Distil\Criterion from a string, you can't always cast that string value to the appropriate value type. Therefor, Distil allows you to define keywords for some specific values.

Working with keyword values

Let's illustrate this with an example and create a Limit filter. The value contained by this filter should either be an integer or null (aka, there is no limit):

use Distil\Criterion;

final class Limit implements Criterion
{
    public function __construct(?int $value)
    {
        $this->value = $value;
    }
    
    public static function fromString(string $value): self
    {
        return new self((int) $value);
    }

    public function name(): string
    {
        return 'limit';
    }
    
    public function value(): ?int
    {
        return $this->value;
    }
}

If we were to offer this as a filter on, for example, a public API, we'd want to be able to resolve limit=unlimited to new Limit(null). 'unlimited' can't be naturally casted to a null value, so we need to register it as a keyword. To do so, our limit Criterion needs to implement the Distil\Keywords\HasKeywords interface, which requires you to define a keywords() method:

use Distil\Criterion;
use Distil\Keywords\HasKeywords;
use Distil\Keywords\Keyword;

final class Limit implements Criterion, HasKeywords
{
    ...
    
    public static function fromString(string $value): self
    {
        $value = (new Keyword(self::class, $value))->value();
        
        return new self($value ? (int) $value : $value);
    }
    
    public static function keywords(): array
    {
        return ['unlimited' => null];
    }
}

Note the usage of the Distil\Keywords\Keyword class in our fromString() constructor. It's a small value object that accepts the Criterion class name and the given string value on construction. Using the keywords() method, it can check whether or not the given string value is a keyword for another value. If it is, the actual value will be returned:

new Limit(null) == Limit::fromString('unlimited'); // true

Now, imagine you'd want to be able to cast the Criterion value back to a string. Using the Distil\Keywords\Value class, you can easily derive the keyword for a value:

use Distil\Criterion;
use Distil\Keywords\HasKeywords;
use Distil\Keywords\Keyword;

final class Limit implements Criterion, HasKeywords
{
    ...
    
    public static function keywords(): array
    {
        return ['unlimited' => null];
    }
    
    public function __toString(): string
    {
        return (new Value($this, $this->value))->keyword() ?: (string) $this->value;
    }
}

If the value is associated with a keyword, the keyword will be returned. If it isn't, we'll get null:

(string) Limit::fromString('unlimited') === 'unlimited'; // true

Note: Limit was simply used here as an example. It's actually available out of the box. Make sure to check out the Common Criteria section.

Keywords on Typed Criteria

As mentioned in the Typed Criteria section, any Criterion instance that extends either one of the Distil\Types automatically handles keywords when created from or casted to a string. This means you only need to implement the Distil\Keywords\HasKeywords interface without having to overwrite the fromString() or __toString() methods.

In addition, any instances of Distil\Types\BooleanCriterion will automatically handle 'true' and 'false' string values.

Common Criteria

Distil provides a couple of common criteria out of the box:

Limit

Distil\Common\Limit is Criterion implementation that wraps around an integer or null value. It does not extend a Criterion Type, but has the same capabilities as any of them:

  • It can be constructed from a string value through the fromString named constructor.
  • When constructed from a string value, it accepts the "unlimited" keyword (which is mapped to null).
  • It can be casted to a string.
  • It can be used as a Criteria factory.

In addition, Limit has a default value (being 10). So you can instantiate it without any arguments:

$limit = new Distil\Common\Limit();

$limit->value(); // Returns 10, its default value

Sort

Distil\Common\Sort is an extension of Distil\Types\ListCriterion. It accepts a list of field or properties by which a result set should be sorted:

$sort = new Distil\Common\Sort('-name', 'created_at');

Note the usage of the "-" sign in front of the "name" property to indicate the result set should be sorted in descending order on that property.

Its value() method simply returns an array containing those sort fields, but you can also retrieve them as small Distil\Common\SortField value objects:

use Distil\Common\SortField;

$sort = new Distil\Common\Sort('-name');

$sort->sortFields() == [new SortField('name', SortField::DESC)];

Factories

Criteria Factories

Any Criterion instance that extends either one of the Distil\Types can also be used as Distil\Criteria factories:

new Distil\Criteria(new Author($authorId));

// can be rewritten as...

Author::criteria($authorId);

Under the hood, this named constructor will delegate its arguments to the Criterion's default constructor, and pass itself along a new Distil\Criteria instance.

If you want to enable using a Criterion as Criteria factory without extending any of the available Criterion Types, you can use the Distil\ActsAsCriteriaFactory trait.

CriterionFactory

In some cases, you may want to instantiate a Criterion by name. Take the following snippet from the example at the top of the docs:

$criteria = new Distil\Criteria();

if (isset($requestData['sort'])) {
    $criteria->add(new Sort($requestData['sort']));
}

if (isset($requestData['limit'])) {
    $criteria->add(Limit::fromString($requestData['limit']));
}

...

Rather than doing this in every controller that may use the Sort and Limit criteria, you can register a resolvers for them in the Distil\CriterionFactory. A resolver is either a class name or a callable (e.g. named constructor, anonumous function, ...) that actually instantiates the Criterion:

// Note that these resolvers could be injected into the factory through your IoC container.
$factory = new Distil\CriterionFactory([
    'sort' => Distil\Common\Sort::class,
    'limit' => Distil\Common\Limit::class.'::fromString',
    'foo' => function () {
        // Some logic to resolve the foo criterion...
    },
]);
$criteria = new Distil\Criteria();

foreach ($requestData as $name => $value) {
    $criteria->add($factory->createByName($name, $value)),
}

Contributing

Please see the contributing file for details.

Changelog

You can see a list of changes for each release in our changelog file.

License

The MIT License. Please see the license file for more information.