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graphql-go

The goal of this project is to provide full support of the GraphQL draft specification 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

Roadmap

We're trying out the GitHub Project feature to manage graphql-go's development roadmap. Feedback is welcome and appreciated.

(Some) Documentation

Basic Sample

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:

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 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 arguments:
- context.Context
- types.FieldDefinition Meta for the GraphQL field that is being resolved.
- types.PathSegment An recursive structure holding all the resolvers i.e. for book.author.name when passed to the name field resolver it will contain the resolvers for author and book also.
- types.SelectedFields Meta for the GraphQL selected fields of a type.
Mandatory arguments if the corresponding GraphQL field has arguments:
- *struct { ... } The names of the struct fields have to be exported and have to match the names of the GraphQL arguments in a non-case-sensitive way. or
- map[string]interface{} Provides a non-type checked way of receiving all passed arguments to the GraphQL field.

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:

func (r *helloWorldResolver) Hello() string {
	return "Hello world!"
}

The following signature is also allowed:

func (r *helloWorldResolver) Hello(ctx context.Context) (string, error) {
	return "Hello world!", nil
}

And with all available arguments:

func (r *helloWorldResolver) Hello(ctx context.Context, fieldDefinition types.FieldDefinition, pathSegment types.PathSegment, args map[string]interface{}) (string, error) {
	return "Hello world!", nil
}

The type checked args struct can be used in place of the map.

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.
UseDefaultResolvers(defaultResolversProvider types.DefaultResolversProvider) allows for passing a struct for providing a field resolver dynamically. It requires the struct to have a GetResolver(fieldDefinition types.FieldDefinition) *types.ResolverInfo method which will be invoked for each field and return a types.ResolverInfo which will be used for resolving the field.
UseDynamicResolvers() specifies whether to allow the resolvers to return a generic struct for resolving the fields. Once enabled the resolvers can return a types.DynamicResolver struct. Usinng this struct for resolving skips the type checking of the return result.
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:

type ResolverError interface {
	error
	Extensions() map[string]interface{}
}

Example of a simple custom error:

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:

{
  "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
}

License

Kinvey/graphql-go

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