Deferred resolving doesn't seem to work

[Jalle19]

There's something wrong with it. In the test we end up calling loadBuffered() twice, which shouldn't happen. There's also both $directorIds and $authors, which seems wrong. Gotta look this through carefully.

[Jalle19]

Related to #320

[crisu83]

@Jalle19 I took a look at this and you're right. The issue is that the promise is resolved immediately. I need to do some research. It might be that we need to introduce our own Deferred concept, like they have done in Webonyx implementation. I don't like the idea, but if it that's what it takes then we'll do that.

[inanc-g]

Any news on this?

[Jalle19]

@crisu83 do you have time to look into this?

[Jalle19]

or @hungneox

[acelot]

Confirm this issue. loadBuffered() is called everytime.

[acelot]

Guys, this issue is critical for production use. Do you have any suggestions? If you do not have time, tell me which way to dig?

[asheliahut]

This is literally the only reason I haven't swapped to this over my Youshido Fork.

[crisu83]

@acelot I have my hands full right now with work, but the easiest way to look at it is to debug the deferred resolver test cases. I think that the main issue is related to how we're handling promises when executing them. CC @hungneox

[asheliahut]

Is there any thought to use https://github.com/overblog/dataloader-php
to solve the problem like almost everyone in node does?

[acelot]

I'm trying to adapt this library for my reactphp-project. I was able to perform a deferred request using lordthorzonus/php-dataloader. But for this I had to change the graphql-php code to support async calls. Because the existing executor have a race condition problem Execution::execute():

if ($data instanceof PromiseInterface) {
    $data->then(function ($resolvedData) use (&$data) {
        $data = $resolvedData;
    });
}

<...>

return new ExecutionResult($data, $context->getErrors());

In this section of the code, the $data variable will always be null and will throw an exception.
To add support for asynchronous calls, I suggest adding a new method promiseExecute which implements new PromisedExecutionInterface:

class Execution implements ExecutionInterface, PromisedExecutionInterface
{
    <...>

    public function promiseExecute(
        Schema $schema,
        DocumentNode $documentNode,
        $rootValue = null,
        $contextValue = null,
        array $variableValues = [],
        ?string $operationName = null,
        ?callable $fieldResolver = null,
        ?ErrorHandlerInterface $errorHandler = null
    ): PromiseInterface {
        <...>

        if ($data instanceof PromiseInterface) {
            return $data->then(function ($resolvedData) use ($context) {
                return new ExecutionResult($resolvedData, $context->getErrors());
            });
        }

        <...>

        return resolve(new ExecutionResult($data, $context->getErrors()));
    }

    <...>
}

I can provide PR, but I need help with tests.

[Jalle19]

@acelot PRs are more than welcome, I'll help you out with the tests!

[acelot]

@Jalle19 #345

[crisu83]

@acelot is this issue resolved?

[acelot]

Yes, completely.