Cynic
Cynic is a GraphQL query builder & data mapper for Rust.
See the README on GitHub for more details.
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
query_dsl
macro to generate a query_dsl for your schema:
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.
- Definitons 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 query_dsl
module.
It's not ideal, but at least provides some visibility into the various enum types.
Creating QueryFragments
Now that you have a query_dsl 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
:
#
// 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:
// You can then build a `cynic::Query` from this fragment
use QueryFragment;
let query = new;
query
above implements serde::Serialize
so can be used with any HTTP
client. For example, with reqwest
:
let response = new
.post
.json
.send?;
let result = query.decode_response?;
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:
#
#
#
#
// 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.
// You can now define a query to use these arguments on. For example, to make
// `FilmDirectorQuery` a bit more dynamic:
// Then we can build a query using this new struct;
use QueryFragment;
let query = new;