Support resource identity as a pair of type and id (array)

[neomerx]

An idea from @lindyhopchris to support relationships not only as classes with empty attributes but as a pair of type and identity as well

public function getRelationships($comment, $includedRelationships = [])
{
    return [
        'author' => [
            static::DATA => isset($includedRelationships['author']) ? 
                $comment->getAuthor() :
                [AuthorSchema::class, $comment->author_id],
        ],
    ];
}

[neomerx]

@lindyhopchris btw $includedRelationships will have relationships not only as values but as keys as well. I guess isset/has_key should work faster.

[neomerx]

I've made a small patch not related to this issue in this branch. It improves scrutinizer's ranking (9.42▲+0.06) and synthetic speed test for about 5-7% (I got 12% once).

[neomerx]

@lindyhopchris An array is probably not gonna work. It can be confused with an array of ordinary resources. Probably something like ResourceIdentifierInterface is a better candidate. Which btw might have an embedded schema.

[neomerx]

I've played a little with code for this enhancement and came up to the following idea.
Add createIdentity method to Schema so it could be used in relationships as

public function getRelationships($comment, $includedRelationships = [])
{
    return [
        'author' => [
            static::DATA => isset($includedRelationships['author']) ? 
                $comment->getAuthor() : $this->createIdentity(Author::class, $comment->author_id)
        ],
    ];
}

The implementation solution will include

• a new DataIdentity class for storing model's class and id.
• changes to SchemaProvider so it can separate handling of DataIdentity from other classes. It will take model's class from DataIdentity, find a Schema for that model class and create a special schema wrapper DataIdentitySchema
• DataIdentitySchema will be built-in Schema that passes all requests to underlying Schema apart those that has $resource as input parameter (e.g. getAttributes, getRelationsips, getId). It will return id from DataIdentity in getId and rise exception for others as it has no real resource data.

[neomerx]

Also there is a simpler alternative. For cases when a model could not be created with just id and any other attributes (I'm still in doubts why such model could not be created) a simple classes could be created for such models with theirs Schemas. For example

class AuthorIdentity
{
    public id;
}

and its Schema

class AuthorIdentitySchema extends DataIdentitySchemaProvider
{
    protected $resourceType = AuthorSchema::TYPE;
    protected $selfSubUrl   = AuthorSchema::SUB_URL;

    public function getId($authorIdentity)
    {
        return $authorIdentity->id;
    }
}

DataIdentitySchemaProvider will just add empty implementation for getAttributes

As I see this issue a rare case and it has a simple solution I tend to think we should not make the implementation more complex and process with this issue. I propose close the issue.