Deserialize a map with one field and extract only the field's value

help
1

I'm writing a (non-general-purpose) GraphQL client, so I often end up having to deserialize JSON maps like {"repository": DATA} that contain only one field where I want to end up with only that field's value. So far, I've just been doing this by defining a bunch of types like:

#[derive(Deserialize)]
struct Response {
    repository: InterestingData,
}

and then just returning the repository field of the deserialized Response, but this is repetitive. I tried to at least get rid of all the singleton struct definitions by instead deserializing to (InterestingData,) and returning the .0 field (thinking that, if a JSON list can be deserialized to a struct, surely deserializing the other way would work), but serde-json didn't like that. serde_with didn't seem to have anything helpful for this either.

At the moment, it looks like my best option is to define a struct Singleton<T>(pub T) type and give it a custom Deserialize impl that expects a one-field map & extracts the field's value, but I'm wondering if there's another way I've overlooked.

2

Someone else just asked the same question Deserialize and serialize struct to map with a single field

3

Despite the similar titles, that question appears to be quite different. Among other things, it looks like that asker wants to be able to retrieve the field name.

4

Try this: Rust Playground

5

That's the sort of thing I was referring to with my Singleton<T> idea in my original post. My question is not how to implement that type specifically; it is whether there are any other approaches (using either serde's built-in features or a third-party library) that would solve my problem without me having to define a custom type or custom Deserialize impl.

6

No, I don't think so. Unless you want to implement you own Deserialize proc-macro.

7

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