Support for omitting fields from the schema

[untitaker]

I would like schemars to honor serde(skip) and schemars(skip) to be able to omit internal datastructures. Ex:

#[derive(JsonSchema)]
struct Foo {
    #[schemars(skip)]
    bar: String
}

would generate a schema against which the input {} validates.

[GREsau]

This is already implemented - when I run

use schemars::{schema_for, JsonSchema};

#[derive(JsonSchema)]
struct Foo {
    #[schemars(skip)]
    bar: String
}

fn main() {
    let schema = schema_for!(Foo);
    println!("{}", serde_json::to_string_pretty(&schema).unwrap());
}

It outputs:

{
  "$schema": "http://json-schema.org/draft-07/schema#",
  "title": "Foo",
  "type": "object"
}

Have you encountered a case where this doesn't happen?

[untitaker]

You're right it does, sorry for the noise. The actual issue I am running into is that all of the schemas generated by schemars do not have additionalProperties set to false, so this attempt failed:

#[derive(JsonSchema)]
struct Foo {
    #[schemars(skip)]
    #[serde(other)]
    extra_data: ...
}

Is there a way to generically set the default of additionalProperties?

[GREsau]

The #[serde(other)] attribute is not valid in your example. If you're trying to add a field that contains all additional properties when desrializing, then this would be done with the #[serde(flatten)] attribute as documented here: https://serde.rs/attr-flatten.html#capture-additional-fields

And in this case, additionalProperties will be set to true, e.g.

#[derive(JsonSchema)]
struct Foo {
    bar: String,
    #[serde(flatten)]
    extra: HashMap<String, Value>,
}

Outputs:

{
  "$schema": "http://json-schema.org/draft-07/schema#",
  "title": "Foo",
  "type": "object",
  "required": [
    "bar"
  ],
  "properties": {
    "bar": {
      "type": "string"
    }
  },
  "additionalProperties": true
}

Unless you added #[schemars(skip)] to the extra field, in which case additionalProperties would not be set.

[GREsau]

Schemars doesn't set additionalProperties to false in derived schemas, mainly because serde allows unknown properties by default.

If you have a struct with #[serde(deny_unknown_fields)], then it would make sense for the schema to set additionalProperties to false. I've planned on implementing that for a while (hence this comment!), it's just one of the things I haven't got around to and no-one's asked for

[untitaker]

Thanks, I did mean flatten. The real background is that we are using a custom deserialization library other than serde and I was trying to keep the examples short.

I am a bit confused why you are either setting additionalProperties=true vs omitting it, as omission is the same thing as setting it to true afaik.

In any case deny_unknown_fields across all structs is likely closest to what I would need as our deserialization framework's default behavior diverges from serde here.

[untitaker]

I'm going to close this since the underlying feature I am missing is already tracked in sourcecode and this thread is quite long-winded.