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# graphql-go [](https://sourcegraph.com/github.com/graph-gophers/graphql-go?badge) [](https://graph-gophers.semaphoreci.com/projects/graphql-go) [](https://godoc.org/github.com/graph-gophers/graphql-go)
<p align="center"><img src="docs/img/logo.png" width="300"></p>
The goal of this project is to provide full support of the [GraphQL draft specification](https://facebook.github.io/graphql/draft) with a set of idiomatic, easy to use Go packages.
While still under heavy development (`internal` APIs are almost certainly subject to change), this library is
safe for production use.
## Features
- minimal API
- support for `context.Context`
- support for the `OpenTracing` standard
- schema type-checking against resolvers
- resolvers are matched to the schema based on method sets (can resolve a GraphQL schema with a Go interface or Go struct).
- handles panics in resolvers
- parallel execution of resolvers
- subscriptions
- [sample WS transport](https://github.com/graph-gophers/graphql-transport-ws)
## Roadmap
We're trying out the GitHub Project feature to manage `graphql-go`'s [development roadmap](https://github.com/graph-gophers/graphql-go/projects/1).
Feedback is welcome and appreciated.
## (Some) Documentation
### Basic Sample
```go
package main
import (
"log"
"net/http"
graphql "github.com/graph-gophers/graphql-go"
"github.com/graph-gophers/graphql-go/relay"
)
type query struct{}
func (_ *query) Hello() string { return "Hello, world!" }
func main() {
s := `
type Query {
hello: String!
}
`
schema := graphql.MustParseSchema(s, &query{})
http.Handle("/query", &relay.Handler{Schema: schema})
log.Fatal(http.ListenAndServe(":8080", nil))
}
```
To test:
```sh
curl -XPOST -d '{"query": "{ hello }"}' localhost:8080/query
```
### Resolvers
A resolver must have one method or field for each field of the GraphQL type it resolves. The method or field name has to be [exported](https://golang.org/ref/spec#Exported_identifiers) and match the schema's field's name in a non-case-sensitive way.
You can use struct fields as resolvers by using `SchemaOpt: UseFieldResolvers()`. For example,
```
opts := []graphql.SchemaOpt{graphql.UseFieldResolvers()}
schema := graphql.MustParseSchema(s, &query{}, opts...)
```
When using `UseFieldResolvers` schema option, a struct field will be used *only* when:
- there is no method for a struct field
- a struct field does not implement an interface method
- a struct field does not have arguments
The method has up to two arguments:
- Optional `context.Context` argument.
- Mandatory `*struct { ... }` argument if the corresponding GraphQL field has arguments. The names of the struct fields have to be [exported](https://golang.org/ref/spec#Exported_identifiers) and have to match the names of the GraphQL arguments in a non-case-sensitive way.
The method has up to two results:
- The GraphQL field's value as determined by the resolver.
- Optional `error` result.
Example for a simple resolver method:
```go
func (r *helloWorldResolver) Hello() string {
return "Hello world!"
}
```
The following signature is also allowed:
```go
func (r *helloWorldResolver) Hello(ctx context.Context) (string, error) {
return "Hello world!", nil
}
```
### Schema Options
- `UseStringDescriptions()` enables the usage of double quoted and triple quoted. When this is not enabled, comments are parsed as descriptions instead.
- `UseFieldResolvers()` specifies whether to use struct field resolvers.
- `MaxDepth(n int)` specifies the maximum field nesting depth in a query. The default is 0 which disables max depth checking.
- `MaxParallelism(n int)` specifies the maximum number of resolvers per request allowed to run in parallel. The default is 10.
- `Tracer(tracer trace.Tracer)` is used to trace queries and fields. It defaults to `trace.OpenTracingTracer`.
- `ValidationTracer(tracer trace.ValidationTracer)` is used to trace validation errors. It defaults to `trace.NoopValidationTracer`.
- `Logger(logger log.Logger)` is used to log panics during query execution. It defaults to `exec.DefaultLogger`.
- `PanicHandler(panicHandler errors.PanicHandler)` is used to transform panics into errors during query execution. It defaults to `errors.DefaultPanicHandler`.
- `DisableIntrospection()` disables introspection queries.
### Custom Errors
Errors returned by resolvers can include custom extensions by implementing the `ResolverError` interface:
```go
type ResolverError interface {
error
Extensions() map[string]interface{}
}
```
Example of a simple custom error:
```go
type droidNotFoundError struct {
Code string `json:"code"`
Message string `json:"message"`
}
func (e droidNotFoundError) Error() string {
return fmt.Sprintf("error [%s]: %s", e.Code, e.Message)
}
func (e droidNotFoundError) Extensions() map[string]interface{} {
return map[string]interface{}{
"code": e.Code,
"message": e.Message,
}
}
```
Which could produce a GraphQL error such as:
```go
{
"errors": [
{
"message": "error [NotFound]: This is not the droid you are looking for",
"path": [
"droid"
],
"extensions": {
"code": "NotFound",
"message": "This is not the droid you are looking for"
}
}
],
"data": null
}
```
### [Examples](https://github.com/graph-gophers/graphql-go/wiki/Examples)
### [Companies that use this library](https://github.com/graph-gophers/graphql-go/wiki/Users)
|
