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< h1 id = "non-struct-objects" > < a class = "header" href = "#non-struct-objects" > Non-struct objects< / a > < / h1 >
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< p > Up until now, we've only looked at mapping structs to GraphQL objects. However,
any Rust type can be mapped into a GraphQL object. In this chapter, we'll look
at enums, but traits will work too - they don't < em > have< / em > to be mapped into GraphQL
interfaces.< / p >
< p > Using < code > Result< / code > -like enums can be a useful way of reporting e.g. validation
errors from a mutation:< / p >
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< pre > < pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > extern crate juniper;
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< / span > < span class = "boring" > use juniper::{graphql_object, GraphQLObject};
< / span > < span class = "boring" > #[derive(juniper::GraphQLObject)] struct User { name: String }
< / span > < span class = "boring" >
< / span > #[derive(GraphQLObject)]
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struct ValidationError {
field: String,
message: String,
}
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< span class = "boring" > #[allow(dead_code)]
< / span > enum SignUpResult {
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Ok(User),
Error(Vec< ValidationError> ),
}
#[graphql_object]
impl SignUpResult {
fn user(& self) -> Option< & User> {
match *self {
SignUpResult::Ok(ref user) => Some(user),
SignUpResult::Error(_) => None,
}
}
fn error(& self) -> Option< & Vec< ValidationError> > {
match *self {
SignUpResult::Ok(_) => None,
SignUpResult::Error(ref errors) => Some(errors)
}
}
}
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< / span > < span class = "boring" > fn main() {}
< / span > < / code > < / pre > < / pre >
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< p > Here, we use an enum to decide whether a user's input data was valid or not, and
it could be used as the result of e.g. a sign up mutation.< / p >
< p > While this is an example of how you could use something other than a struct to
represent a GraphQL object, it's also an example on how you could implement
error handling for " expected" errors - errors like validation errors. There are
no hard rules on how to represent errors in GraphQL, but there are
< a href = "https://github.com/facebook/graphql/issues/117#issuecomment-170180628" > some< / a >
< a href = "https://github.com/graphql/graphql-js/issues/560#issuecomment-259508214" > comments< / a >
from one of the authors of GraphQL on how they intended " hard" field errors to
be used, and how to model expected errors.< / p >
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