74 lines
2.1 KiB
Markdown
74 lines
2.1 KiB
Markdown
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# Introspection
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GraphQL defines a special built-in top-level field called `__schema`. Querying
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for this field allows one to [introspect the schema](https://graphql.org/learn/introspection/)
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at runtime to see what queries and mutations the GraphQL server supports.
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Because introspection queries are just regular GraphQL queries, Juniper supports
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them natively. For example, to get all the names of the types supported one
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could execute the following query against Juniper:
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```graphql
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{
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__schema {
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types {
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name
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}
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}
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}
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```
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## Schema introspection output as JSON
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Many client libraries and tools in the GraphQL ecosystem require a complete
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representation of the server schema. Often this representation is in JSON and
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referred to as `schema.json`. A complete representation of the schema can be
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produced by issuing a specially crafted introspection query.
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Juniper provides a convenience function to introspect the entire schema. The
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result can then be converted to JSON for use with tools and libraries such as
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[graphql-client](https://github.com/graphql-rust/graphql-client):
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```rust
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# // Only needed due to 2018 edition because the macro is not accessible.
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# extern crate juniper;
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# extern crate serde_json;
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use juniper::{EmptyMutation, FieldResult, IntrospectionFormat};
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// Define our schema.
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#[derive(juniper::GraphQLObject)]
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struct Example {
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id: String,
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}
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struct Context;
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impl juniper::Context for Context {}
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struct Query;
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juniper::graphql_object!(Query: Context |&self| {
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field example(&executor, id: String) -> FieldResult<Example> {
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unimplemented!()
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}
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});
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type Schema = juniper::RootNode<'static, Query, EmptyMutation<Context>>;
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fn main() {
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// Create a context object.
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let ctx = Context{};
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// Run the built-in introspection query.
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let (res, _errors) = juniper::introspect(
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&Schema::new(Query, EmptyMutation::new()),
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&ctx,
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IntrospectionFormat::default(),
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).unwrap();
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// Convert introspection result to json.
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let json_result = serde_json::to_string_pretty(&res);
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assert!(json_result.is_ok());
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}
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```
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