Expand description
§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.
§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:
mod schema {
cynic::use_schema!("../schemas/starwars.schema.graphql");
}
This macro generates a few things:
- Some structs to represent the Input types the underlying schema. You may need to use these to build mutations or as parameters to queries.
- Definitions of all the Enums in the provided schema. You’ll need these if you want to use any enum types.
- 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
:
#[derive(cynic::QueryFragment)]
#[cynic(schema_path = "../schemas/starwars.schema.graphql")]
struct Film {
title: Option<String>,
director: Option<String>,
}
// 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<Film>,
}
// 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
let response = reqwest::blocking::Client::new()
.post("a_url")
.json(&operation)
.send()?;
let result = response.json::<GraphQlResponse<FilmDirectorQuery>>()?;
After this code has run, result will be an instance of
GraphQlResponse<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:
// Deriving `QueryVariables` allows this struct to be used as variables in a
// `QueryFragment`, whether it represents part of a query or a whole query.
#[derive(cynic::QueryVariables)]
struct FilmArguments {
id: Option<cynic::Id>,
}
// 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 `variables` parameter to our `QueryFragment` we've made a variable
// named `args` available for use in the `arguments` attribute.
variables = "FilmArguments"
)]
struct FilmDirectorQueryWithArgs {
// Here we use `args`, which we've declared above to be an instance of `FilmArguments`
#[arguments(id: $id)]
film: Option<Film>,
}
// 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.
http-surf
adds integration with thesurf
http client.http-reqwest
adds async integration with thereqwest
http client.http-reqwest-blocking
adds blocking integration with thereqwest
http client.rkyv
can be used to speed up compiles when working with large schemas.
It’s worth noting that each of these features pulls in extra
dependencies, which may impact your build size. Particularly
if you’re targeting WASM. In particular the url
crate has
known issues when
targeting web assembly.
Re-exports§
pub use variables::QueryVariableLiterals;
pub use variables::QueryVariables;
pub use variables::QueryVariablesFields;
pub use serde;
Modules§
- Tools for enforcing the GraphQL coercion rules
- HTTP client support for cynic.
- Tools for building GraphQL queries in cynic
- Traits for describing a GraphQL schema in Rust.
- Types & traits for working with GraphQL Variables
Macros§
- Asserts that the type implements all of the given traits.
- Asserts that all types in a list are equal to each other.
- Implements the default GraphQL list & option coercion rules for a type.
- Implements a set of scalar traits for the given type & type lock.
- Imports a schema for use by cynic.
Structs§
- A model describing an error which has taken place during execution.
- A line and column offset describing the location of an error within a GraphQL document.
- The response to a GraphQl operation
- A GraphQL
ID
- An Operation that can be sent to a remote GraphQL server.
- Low level builder for Operation.
- A StreamingOperation is an Operation that expects a stream of results.
Enums§
- A segment of a GraphQL error path.
- Errors that can occur when building the operation
Traits§
- A GraphQL Enum.
- A QueryFragment that contains a set of inline fragments
- A GraphQL input object.
- Provides a
build
function onQueryFragment
s that represent a mutation - Provides a
build
function onQueryFragment
s that represent a query - A trait that marks a type as part of a GraphQL query.
- Provides a
build
function onQueryFragment
s that represent a subscription
Attribute Macros§
- Imports a registered schema into a schema module.
- An attribute macro to automatically add schema attributes to cynic derives.
Derive Macros§
- Derives
cynic::Enum
- Derives
cynic::InlineFragments
- Derives
InputObject
- Derives
cynic::QueryFragment
- Derives
cynic::QueryVariableLiterals
- Derives
cynic::QueryVariables
- Derives
cynic::Scalar