stuartc
Generating JSON responses as a stream
I’m trying to generate a stream of JSON from an Ecto stream to be sent out via send_chunked/2 and chunk/2.
It appears that all the JSON libraries I can find are only for parsing.
With the exception of GitHub - TreyE/json_stream_encoder: Streaming encoder for JSON in elixir. · GitHub
I got stuck trying to use this library since it’s built around IO.binwrite which needs an IO device; I’m more comfortable with streams at the moment.
The gist of what I need is IO’ish device or a Stream of strings, but gives me the opportunity to format things as I go.
Individual items in the response aren’t big on their own, but there could be thousands of them.
Is there any library or approach anyone can share?
Marked As Solved
LostKobrakai
Ecto streams are not arbitrary, but essentially chunks. You always get a fixed(max) number of full rows, never partial rows. So your stream could essentially be:
rows = Stream.map(ecto_stream, &Jason.encode!/1)
Stream.concat([["["], Stream.intersperse(rows, ","), ["]"]])
Or switch to ndjson and just join the rows with newlines.
Also Liked
krasenyp
They might even query records as JSON, if the database supports it, and skip encoding in the application altogether.
Last Post!
LostKobrakai
Yeah. Stream vs Enum APIs is about the output, not the input. The inputs are usually similar / the same and accept any Enumerables.
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