Generating custom links in middleware and request handlers

In most cases, you can rely on the ResourceGenerator to generate self relational links, and, in the case of paginated collections, pagination links.

What if you want to generate other links to include in your resources, though?

The ResourceGenerator provides access to the metadata map, hydrators, and link generator via getter methods:

  • getMetadataMap()
  • getHydrators()
  • getLinkGenerator()

We can thus use these in order to generate custom links as needed.

In our first scenario, we'll create a "search" link for a resource.

We'll assume that you have composed a ResourceGenerator instance in your middleware, and assigned it to the $resourceGenerator property.

The link we want to generate will look something like /api/books?query={searchParms}, and map to a route named books.

$searchLink = $this->resourceGenerator
    ->getLinkGenerator()
    ->templatedFromRoute(
        'search',
        $request,
        'books',
        [],
        ['query' => '{searchTerms}']
    );

You could then compose it in your resource:

$resource = $resource->withLink($searchLink);

In our second scenario, we'll consider a collection endpoint. It might include a per_page query string argument, to allow defining how many results to return per page, a sort argument, and a query argument indicating the search string. We know these at runtime, but not at the time we create our configuration, so we need to inject them after we have our metadata created, but before we generate our resource, so that the pagination links are correctly generated.

$queryParams = $request->getQueryParams();
$query       = $queryParams['query'] ?? '';
$perPage     = $queryParams['per_page'] ?? 25;
$sort        = $queryParams['sort'] ?? '';
$metadataMap = $this->resourceGenerator->getMetadataMap();
$metadata    = $metadataMap->get(BookCollection::class);

$metadataQuery = $origMetadataQuery = $metadata->getQueryStringArguments();

if ('' !== $query) {
    $metadataQuery = array_merge($metadataQuery, ['query' => $query]);
}

if ('' !== $perPage) {
    $metadataQuery = array_merge($metadataQuery, ['per_page' => $perPage]);
}

if ('' !== $sort) {
    $metadataQuery = array_merge($metadataQuery, ['sort' => $sort]);
}

$metadata->setQueryStringArguments($metadataQuery);

// ...

$resource = $this->resourceGenerator->fromObject($books, $request);

// Reset query string arguments
$metadata->setQueryStringArguments($origMetadataQuery);

This will lead to links with URIs such as /api/books?query=Adams&per_page=5&sort=DESC&page=4.

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