40 lines
1.1 KiB
Markdown
40 lines
1.1 KiB
Markdown
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# Custom directive
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`Async-graphql` can easily customize directives, which can extend the behavior of GraphQL.
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To create a custom directive, you need to implement the `CustomDirective` trait, and then use the `Directive` macro to
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generate a factory function that receives the parameters of the directive and returns an instance of the directive.
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Currently `Async-graphql` only supports directive located at `FIELD`.
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```rust
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struct ConcatDirective {
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value: String,
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}
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#[async_trait::async_trait]
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impl CustomDirective for ConcatDirective {
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async fn resolve_field(&self, _ctx: &Context<'_>, resolve: ResolveFut<'_>) -> ServerResult<Option<Value>> {
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resolve.await.map(|value| {
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value.map(|value| match value {
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Value::String(str) => Value::String(str + &self.value),
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_ => value,
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})
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})
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}
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}
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#[Directive(location = "field")]
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fn concat(value: String) -> impl CustomDirective {
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ConcatDirective { value }
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}
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```
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Register the directive when building the schema:
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```rust
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let schema = Schema::build(Query, EmptyMutation, EmptySubscription)
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.directive(concat)
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.finish();
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```
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