# Cynic
Cynic is a GraphQL query builder & data mapper for Rust.
This documentation is primarily intended to be a reference for specific functions,
for a guide to using `Cynic` see the website: [cynic-rs.dev](https://cynic-rs.dev).
## Overview
To get started with Cynic you'll need a GraphQL schema for the API you wish to
query. The examples will be using the star wars API.
### Generating a Query DSL
Once you've got your schema installed locally, you'll need to use the
`use_schema` macro to generate a schema module:
```rust
mod schema {
cynic::use_schema!("../schemas/starwars.schema.graphql");
}
```
This macro generates a few things:
1. Some structs to represent the Input types the underlying schema.
You may need to use these to build mutations or as parameters to queries.
2. Definitons of all the Enums in the provided schema. You'll need these if
you want to use any enum types.
3. Type safe selection set functions. These can be used to build up a query
manually, though it's usually easier to use the `QueryFragment` derive
functionality explained below. Hopefully you'll not need to use these
directly too often.
Though using macros to generate these is convenient, it does leave a lot of code
to the imagination. You can get a glimpse of the things this defines by running
`cargo doc --document-private-items` and having a look in the `schema` module.
It's not ideal, but at least provides some visibility into the various enum types.
### Creating QueryFragments
Now that you have a schema defined, you can start building some queries.
Cynic lets you do this by deriving `QueryFragment` for a struct. For example,
if we wanted to know what director title & director a Star Wars film had, we
could define this `QueryFragment`:
```rust
# mod schema {
# cynic::use_schema!("../schemas/starwars.schema.graphql");
# }
#[derive(cynic::QueryFragment)]
#[cynic(schema_path = "../schemas/starwars.schema.graphql")]
struct Film {
title: Option,
director: Option
}
// This `Film` struct can now be used as the type of a field on any other
// `QueryFragment` struct and cynic will know how to turn that into a GraphQL
// query, and populate the `Film` struct from the response.
// For example, if we wanted to know the Director for a particular film:
#[derive(cynic::QueryFragment)]
#[cynic(
schema_path = "../schemas/starwars.schema.graphql",
graphql_type = "Root"
)]
struct FilmDirectorQuery {
// Here we use the `#[arguments()]` attribute on the `film` field to provide a
// hard coded film ID to look up. Though useful for demonstration, hard coded
// arguments like this aren't much use in reality. For more details on providing
// runtime arguments please see below.
#[arguments(id = cynic::Id::new("ZmlsbXM6MQ=="))]
film: Option,
}
// You can then build a `cynic::Operation` from this fragment
use cynic::{QueryBuilder};
let operation = FilmDirectorQuery::build(());
```
`operation` above implements `serde::Serialize` so can be used with any HTTP
client. A selection of HTTP client integrations are provided in
`cynic::http` - see the docs there for examples of using a `cynic::Operation`
```rust,ignore
let response = reqwest::blocking::Client::new()
.post("a_url")
.json(&operation)
.send()?;
let result = query.decode_response(response.json()?)?;
```
After this code has run, result will be an instance of `FilmDirectorQuery`
with the film populated appropriately.
### Dynamic Query Arguments
The query above was useful for demonstration, but you'll usually want to be able to
provide parameters to your query. To do this, you should define a struct that contains
all of the parameters you want to provide:
```rust
# mod schema {
# cynic::use_schema!("../schemas/starwars.schema.graphql");
# }
# #[derive(cynic::QueryFragment)]
# #[cynic(
# schema_path = "../schemas/starwars.schema.graphql",
# )]
# struct Film {
# title: Option,
# director: Option
# }
// Deriving `FragmentArguments` allows this struct to be used as arguments to a
// `QueryFragment` fragment, whether it represents part of a query or a whole query.
#[derive(cynic::FragmentArguments)]
struct FilmArguments {
id: Option
}
// You can now define a query to use these arguments on. For example, to make
// `FilmDirectorQuery` a bit more dynamic:
#[derive(cynic::QueryFragment)]
#[cynic(
schema_path = "../schemas/starwars.schema.graphql",
graphql_type = "Root",
// By adding the `argument_struct` parameter to our `QueryFragment` we've made a variable
// named `args` avaiable for use in the `arguments` attribute.
argument_struct = "FilmArguments"
)]
struct FilmDirectorQueryWithArgs {
// Here we use `args`, which we've declared above to be an instance of `FilmArguments`
#[arguments(id = &args.id)]
film: Option,
}
// Then we can build a query using this new struct;
use cynic::QueryBuilder;
let operation = FilmDirectorQueryWithArgs::build(
FilmArguments{ id: Some("ZmlsbXM6MQ==".into()) }
);
```
## Feature Flags
Cynic has a few features that are controlled by feature flags.
- `surf` adds integration with the [`surf`](https://github.com/http-rs/surf)
http client.
- `rewest` adds async integration with the
[`reqwest`](https://github.com/seanmonstar/reqwest) http client.
- `rewest-blocking` adds blocking integration with the
[`reqwest`](https://github.com/seanmonstar/reqwest) http client.
It's worth noting that each of these features pulls in extra
dependencies, which may impact your build size. Particularly
if you're targetting WASM. In particular the `url` crate has
[known issues](https://github.com/servo/rust-url/issues/557) when
targetting web assembly.