graphql-client

To use graphql_client, you need a GraphQL schema (in .graphql or .json format) and a .graphql file containing your query. The library uses a procedural macro to generate typed Rust structures at compile-time.

1. Save your query in a .graphql file.
2. Download your schema (you can use the provided graphql_client_cli).
3. Use the #[derive(GraphQLQuery)] macro on a struct to generate the necessary types.

The macro generates a module named after your struct (in snake case). This module contains:

• ResponseData: The root type for the response.
• Variables: A struct representing the expected query variables.

To send a request, use the GraphQLQuery::build_query(variables) method to create the request payload.

use graphql_client::{GraphQLQuery, Response};
use std::error::Error;
use reqwest;

#[derive(GraphQLQuery)]
#[graphql(
    schema_path = "tests/unions/union_schema.graphql",
    query_path = "tests/unions/union_query.graphql",
    response_derives = "Debug",
)]
pub struct UnionQuery;

async fn perform_my_query(variables: union_query::Variables) -> Result<(), Box<dyn Error>> {
    // this is the important line
    let request_body = UnionQuery::build_query(variables);

    let client = reqwest::Client::new();
    let mut res = client.post("/graphql").json(&request_body).send().await?;
    let response_body: Response<union_query::ResponseData> = res.json().await?;
    println!("{:#?}", response_body);
    Ok(())
}

When graphql-client generates Rust code from a GraphQL schema, it creates Rust enum types for GraphQL enums.

Key behaviors include:

1. Keyword Escaping: Since GraphQL enum variants might use Rust reserved keywords (e.g., self, where), the generator automatically escapes variant names and constructors (e.g., self becomes self_). However, the string representation used for serialization remains the original GraphQL name.
2. The Other(String) Variant: Every generated enum includes an Other(String) variant. This acts as a fallback to ensure the client doesn't crash if the server returns a new enum value that was not present in the schema used during code generation.
3. Serialization/Deserialization: Enums implement serde::Serialize and serde::Deserialize.
   • Serialization: Converts the enum variant to its original GraphQL string name.
   • Deserialization: Attempts to match the incoming string to a known variant. If no match is found, it captures the value in the Other(String) variant instead of returning a deserialization error.