Sputnik: Vec<NestedStruct> serializes snake_case but Option<NestedStruct> is camelCase

While working on a Sputnik satellite I ran into an inconsistency in how nested structs get serialized in typed query results, depending on the container.

An Option<Struct> field comes out camelCase on the JSON side, while a Vec<Struct> of the same record comes out snake_case. So you end up keeping two schemas for the same type, and switching an endpoint between opt and vec can fail at runtime with something like:

Error converting from js 'JsonData' into type 'Candid': missing field 'inviteCode'

From what I could tell it comes from functions-tools/src/converters/zod-to-rust.ts, where the vec case sets needsJsonData: false while opt passes through inner.needsJsonData, so array element structs don't get the #[json_data(nested)] attribute.

Flipping just that isn't enough though, the JsonData derive macro in junobuild/juno (derive.rs) doesn't seem to handle a nested Vec yet (nested_json_data_ident only recurses into Option).

Making vec camelCase would be breaking, so it might need to be opt-in or a major.

fix(leagues): fix join-by-invite trap, return camelCase Option<League> (

Can you provide a code snippet to reproduce the issue?

@peterpeterparker

@peterpeterparker this is the practical case of my repo (simplified):

const ItemSchema = j.strictObject({inviteCode: j.string()});

export const getItem = defineQuery({
  result: j.strictObject({item: ItemSchema.optional()}),
  handler: () => ({item: {inviteCode: 'ABC123'}})
});

export const listItems = defineQuery({
  result: j.strictObject({items: j.array(ItemSchema)}),
  handler: () => ({items: [{inviteCode: 'ABC123'}]})
});

and it generates:

pub struct GetItemResult {
    #[json_data(nested)]
    pub item: Option<GetItemResultItem>,
}

pub struct ListItemsResult {
    pub items: Vec<ListItemsResultItems>,  <-----here no json_data(nested)
}

Or maybe the real handlers affect this outcome? I made them hardcoded to simplify reproduction, but being sincere i did not test it with this specific case. I suppose, the results should be the same

Thanks for the issue and snippet, I can reproduce!

I merged the PR and released the JS lib and integrated it in CLI. However it requires a bit more work as the macros should also be extended #2814. Means, it will require a full release (Juno, Sputnik, Juno Docker, Juno Action).

I'll follow-up and let know when it's released, takes few hours.

The release is out and, using it, I wasn't able to reproduce the issue anymore - i.e. the problem seems to be resolved.

Juno main repo, JS, CLI, Docker, Action and Sputnik have been released.

On your local environment, you can update your CLI and then run juno emulator pull to download the latest version of the emulator - i.e. you'll need both CLI and emulator latest version.

PS: Updating the emulator require to clear the state afterwards

Thanks for the issue and help! Ping me if it ain't resolved on your side, happy to reopen and iterate further.

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Sputnik: `Vec<NestedStruct>` serializes snake_case but `Option<NestedStruct>` is camelCase #2815

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Sputnik: Vec<NestedStruct> serializes snake_case but Option<NestedStruct> is camelCase #2815

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peterpeterparker commented on Jun 5, 2026

AntonioVentilii commented on Jun 5, 2026

peterpeterparker commented on Jun 6, 2026

peterpeterparker commented on Jun 6, 2026

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Sputnik: `Vec<NestedStruct>` serializes snake_case but `Option<NestedStruct>` is camelCase #2815