76 lines
3 KiB
Markdown
76 lines
3 KiB
Markdown
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---
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title: Refactoring to value objects
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pubDate: 2022-10-03
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permalink: archive/2022/10/03/refactoring-value-objects
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tags: [php]
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---
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Here's a snippet of some Drupal code that I wrote last week. It's responsible for converting an array of nodes into a Collection of one of it's field values.
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```php
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return Collection::make($stationNodes)
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->map(fn (NodeInterface $station): string => $station->get('field_station_code')->getString())
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->values();
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```
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There are two issues with this code.
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First, whilst I'm implicitly saying that it accepts a certain type of node, because of the `NodeInterface` typehint this could accept any type of node. If that node doesn't have the required field, the code will error - but I'd like to know sooner if an incorrect type of node is passed and make it explicit that only a certain type of node can be used.
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Second, the code for getting the field values is quite verbose and is potentially repeated in other places within the codebase. I'd like to have a simple way to access these field values that I can reuse anywhere else. If the logic for getting these particular field values changes, then I'd only need to change it in one place.
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## Introducing a value object
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This is the value object that I created.
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It accepts the original node but checks to ensure that the node is the correct type. If not, an Exception is thrown.
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I've added a helper method to get the field value, encapsulating that logic in a reusable function whilst making the code easier to read and its intent clearer.
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```php
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namespace Drupal\mymodule\ValueObject;
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use Drupal\node\NodeInterface;
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final class Station implements StationInterface {
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private NodeInterface $node;
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private function __construct(NodeInterface $node) {
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if ($node->bundle() != 'station') {
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throw new \InvalidArgumentException();
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}
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$this->node = $node;
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}
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public function getStationCode(): string {
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return $this->node->get('field_station_code')->getString();
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}
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public static function fromNode(NodeInterface $node): self {
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return new self($node);
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}
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}
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```
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## Refactoring to use the value object
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This is what my code now looks like:
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```php
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return Collection::make($stationNodes)
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->map(fn (NodeInterface $node): StationInterface => Station::fromNode($node))
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->map(fn (StationInterface $station): string => $station->getStationCode())
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->values();
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```
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<<<<<<< HEAD:website/source/_daily_emails/2022-10-03.md
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=======
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>>>>>>> b9cea6d (chore: replace Sculpin with Astro):website/src/pages/daily-emails/2022-10-03.md
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I've added an additional `map` to convert the nodes to the value object, but the second map can now use the new typehint - ensuring better type safety and also giving us auto-completion in IDEs and text editors. If an incorrect node type is passed in, then the Exception will be thrown and a much clearer error message will be shown.
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Finally, I can use the helper method to get the field value, encapsulating the logic within the value object and making it intention clearer and easier to read.
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