3b7ed74d11
- examples to fix still
- error_extensions.md ResultExt example does not compile!
- trait ErrorExtensions is not implemented for ParseIntError
- dataloader
- requires sqlx to work. So we either "stub" it OR we rewrite them simpler to use a simple "faux" db library
39 lines
1.4 KiB
Markdown
39 lines
1.4 KiB
Markdown
# Error handling
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Resolve can return a `Result`, which has the following definition:
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```rust,ignore
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type Result<T> = std::result::Result<T, Error>;
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```
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Any `Error` that implements `std::fmt::Display` can be converted to `Error` and you can extend the error message.
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The following example shows how to parse an input string to an integer. When parsing fails, it will return an error and attach an error message.
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See the [Error Extensions](error_extensions.md) section of this book for more details.
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```rust
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# extern crate async_graphql;
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# use std::num::ParseIntError;
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use async_graphql::*;
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struct Query;
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#[Object]
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impl Query {
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async fn parse_with_extensions(&self, input: String) -> Result<i32> {
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Ok("234a"
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.parse()
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.map_err(|err: ParseIntError| err.extend_with(|_, e| e.set("code", 400)))?)
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}
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}
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```
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#### Errors in subscriptions
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Errors can be returned from subscription resolvers as well, using a return type of the form:
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```rust,ignore
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async fn my_subscription_resolver(&self) -> impl Stream<Item = Result<MyItem, MyError>> { ... }
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```
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Note however that the `MyError` struct must have `Clone` implemented, due to the restrictions placed by the `Subscription` macro. One way to accomplish this is by creating a custom error type, with `#[derive(Clone)]`, as [seen here](https://github.com/async-graphql/async-graphql/issues/845#issuecomment-1090933464).
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