LazyCollection does not work with json streaming responses

[Sparclex]

Laravel Version

12.34.0

PHP Version

8.4.13

Description

When streaming a LazyCollection as JSON, the response is not actually streamed — instead, the entire dataset is loaded into memory.

I found that this happens because LazyCollection implements JsonSerializable via Enumerable, causing it to be serialized in-memory rather than using StreamedJsonResponse.

Proposed Solution

LazyCollection should override the jsonSerialize method from Enumerable to use a more memory-efficient approach, same as StreamedJsonResponse::streamData.

Steps To Reproduce

https://github.com/Sparclex/lazy-collection-json-memory-issue

Run the migrations an go to the start page. You'll find two links one with a lazy collection implementation and one with a generator function wrapped around the lazy collection (for which streaming works).

[macropay-solutions]

We found out that a json can't be streamed that easily see this: symfony/symfony#60257

This is not an issue from Laravel.

You can stream json lines if you want: https://marius-ciclistu.medium.com/streamed-json-lines-using-laravel-crud-wizard-free-cd650e272caa

[shaedrich]

would be different if this was jsonl

[Sparclex]

As far as I know json can be streamed yet partially incomplete. But this package should be able to read the stream: https://github.com/laravel/stream
My implementation with the generator shows, that it generally works just not with the lazy collection.

[macropay-solutions]

The symfony implementation of StreamedJsonResponse is not streaming. We tested it. If you take the time to read the related issue we opened in their github you will see. If you can stream a json without using json_encode, then maybe it might work with that related laravel stream package. But for that you would want to echo hard coded parts of the json.

[Sparclex]

But for that you would want to echo hard coded parts of the json.

Isn't that exactly what the StreamedJsonResponse is doing? https://github.com/symfony/http-foundation/blob/c061c7c18918b1b64268771aad04b40be41dd2e6/StreamedJsonResponse.php#L130
The only thing it seems missing is flush to faster write to the output buffer. It still uses json_encode, but as long it only json_encodes one Model at a time it would not run out of memory.

[macropay-solutions]

There is no point in duplicating here all the things clarified in that symfony issue. Flush does not work. Read all that thread. They confirmed it.
Just use JSONL if you don't want to waste time on this.

What you asked is just the outher shell of a json. The inner json contains all the data and that is not streamed. json_encode needs all the data to work.