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