graph-gophers · pavelnikolov · Feb 4, 2019 · Oct 30, 2018 · Jan 17, 2019 · Feb 4, 2019
diff --git a/README.md b/README.md
@@ -65,7 +65,17 @@ $ curl -XPOST -d '{"query": "{ hello }"}' localhost:8080/query
 
 ### Resolvers
 
-A resolver must have one method for each field of the GraphQL type it resolves. The method name has to be [exported](https://golang.org/ref/spec#Exported_identifiers) and match the field's name in a non-case-sensitive way.
+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`, a field will be used *only* when:
+- there is no method
+- it does not implement an interface
+- it does not have arguments 
 
 The method has up to two arguments:
 

diff --git a/example/social/README.md b/example/social/README.md
@@ -0,0 +1,9 @@
+### Social App
+
+A simple example of how to use struct fields as resolvers instead of methods.
+
+To run this server
+
+`go run ./example/field-resolvers/server/server.go`
+
+and go to localhost:9011 to interact
diff --git a/example/social/server/server.go b/example/social/server/server.go
@@ -0,0 +1,63 @@
+package main
+
+import (
+	"log"
+	"net/http"
+
+	"github.com/graph-gophers/graphql-go"
+	"github.com/graph-gophers/graphql-go/example/social"
+	"github.com/graph-gophers/graphql-go/relay"
+)
+
+func main() {
+
+	opts := []graphql.SchemaOpt{graphql.UseFieldResolvers(), graphql.MaxParallelism(20)}
+	schema := graphql.MustParseSchema(social.Schema, &social.Resolver{}, opts...)
+
+	http.Handle("/", http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Write(page)
+	}))
+
+	http.Handle("/query", &relay.Handler{Schema: schema})
+
+	log.Fatal(http.ListenAndServe(":9011", nil))
+}
+
+var page = []byte(`
+<!DOCTYPE html>
+<html>
+	<head>
+		<link href="https://cdnjs.cloudflare.com/ajax/libs/graphiql/0.11.11/graphiql.min.css" rel="stylesheet" />
+		<script src="https://cdnjs.cloudflare.com/ajax/libs/es6-promise/4.1.1/es6-promise.auto.min.js"></script>
+		<script src="https://cdnjs.cloudflare.com/ajax/libs/fetch/2.0.3/fetch.min.js"></script>
+		<script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.2.0/umd/react.production.min.js"></script>
+		<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.2.0/umd/react-dom.production.min.js"></script>
+		<script src="https://cdnjs.cloudflare.com/ajax/libs/graphiql/0.11.11/graphiql.min.js"></script>
+	</head>
+	<body style="width: 100%; height: 100%; margin: 0; overflow: hidden;">
+		<div id="graphiql" style="height: 100vh;">Loading...</div>
+		<script>
+			function graphQLFetcher(graphQLParams) {
+				return fetch("/query", {
+					method: "post",
+					body: JSON.stringify(graphQLParams),
+					credentials: "include",
+				}).then(function (response) {
+					return response.text();
+				}).then(function (responseBody) {
+					try {
+						return JSON.parse(responseBody);
+					} catch (error) {
+						return responseBody;
+					}
+				});
+			}
+
+			ReactDOM.render(
+				React.createElement(GraphiQL, {fetcher: graphQLFetcher}),
+				document.getElementById("graphiql")
+			);
+		</script>
+	</body>
+</html>
+`)
diff --git a/example/social/social.go b/example/social/social.go
@@ -0,0 +1,206 @@
+package social
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"strings"
+	"time"
+
+	"github.com/graph-gophers/graphql-go"
+)
+
+const Schema = `
+	schema {
+		query: Query
+	}
+
+	type Query {
+		admin(id: ID!, role: Role = ADMIN): Admin!
+		user(id: ID!): User!
+		search(text: String!): [SearchResult]!
+	}
+
+	interface Admin {
+		id: ID!
+		name: String!
+		role: Role!
+	}
+
+	scalar Time	
+
+	type User implements Admin {
+		id: ID!
+		name: String!
+		email: String!
+		role: Role!
+		phone: String!
+		address: [String!]
+		friends(page: Pagination): [User]
+		createdAt: Time!
+	}
+
+	input Pagination {
+	  	first: Int
+	  	last: Int
+	}
+
+	enum Role {
+		ADMIN
+		USER
+	}
+
+	union SearchResult = User
+`
+
+type page struct {
+	First *float64
+	Last  *float64
+}
+
+type admin interface {
+	ID() graphql.ID
+	Name() string
+	Role() string
+}
+
+type searchResult struct {
+	result interface{}
+}
+
+func (r *searchResult) ToUser() (*user, bool) {
+	res, ok := r.result.(*user)
+	return res, ok
+}
+
+type user struct {
+	IDField   string
+	NameField string
+	RoleField string
+	Email     string
+	Phone     string
+	Address   *[]string
+	Friends   *[]*user
+	CreatedAt graphql.Time
+}
+
+func (u user) ID() graphql.ID {
+	return graphql.ID(u.IDField)
+}
+
+func (u user) Name() string {
+	return u.NameField
+}
+
+func (u user) Role() string {
+	return u.RoleField
+}
+
+func (u user) FriendsResolver(args struct{ Page *page }) (*[]*user, error) {
+	var from int
+	numFriends := len(*u.Friends)
+	to := numFriends
+
+	if args.Page != nil {
+		if args.Page.First != nil {
+			from = int(*args.Page.First)
+			if from > numFriends {
+				return nil, errors.New("not enough users")
+			}
+		}
+		if args.Page.Last != nil {
+			to = int(*args.Page.Last)
+			if to == 0 || to > numFriends {
+				to = numFriends
+			}
+		}
+	}
+
+	friends := (*u.Friends)[from:to]
+
+	return &friends, nil
+}
+
+var users = []*user{
+	{
+		IDField:   "0x01",
+		NameField: "Albus Dumbledore",
+		RoleField: "ADMIN",
+		Email:     "Albus@hogwarts.com",
+		Phone:     "000-000-0000",
+		Address:   &[]string{"Office @ Hogwarts", "where Horcruxes are"},
+		CreatedAt: graphql.Time{Time: time.Now()},
+	},
+	{
+		IDField:   "0x02",
+		NameField: "Harry Potter",
+		RoleField: "USER",
+		Email:     "harry@hogwarts.com",
+		Phone:     "000-000-0001",
+		Address:   &[]string{"123 dorm room @ Hogwarts", "456 random place"},
+		CreatedAt: graphql.Time{Time: time.Now()},
+	},
+	{
+		IDField:   "0x03",
+		NameField: "Hermione Granger",
+		RoleField: "USER",
+		Email:     "hermione@hogwarts.com",
+		Phone:     "000-000-0011",
+		Address:   &[]string{"233 dorm room @ Hogwarts", "786 @ random place"},
+		CreatedAt: graphql.Time{Time: time.Now()},
+	},
+	{
+		IDField:   "0x04",
+		NameField: "Ronald Weasley",
+		RoleField: "USER",
+		Email:     "ronald@hogwarts.com",
+		Phone:     "000-000-0111",
+		Address:   &[]string{"411 dorm room @ Hogwarts", "981 @ random place"},
+		CreatedAt: graphql.Time{Time: time.Now()},
+	},
+}
+
+var usersMap = make(map[string]*user)
+
+func init() {
+	users[0].Friends = &[]*user{users[1]}
+	users[1].Friends = &[]*user{users[0], users[2], users[3]}
+	users[2].Friends = &[]*user{users[1], users[3]}
+	users[3].Friends = &[]*user{users[1], users[2]}
+	for _, usr := range users {
+		usersMap[usr.IDField] = usr
+	}
+}
+
+type Resolver struct{}
+
+func (r *Resolver) Admin(ctx context.Context, args struct {
+	Id   string
+	Role string
+}) (admin, error) {
+	if usr, ok := usersMap[args.Id]; ok {
+		if usr.RoleField == args.Role {
+			return *usr, nil
+		}
+	}
+	err := fmt.Errorf("user with id=%s and role=%s does not exist", args.Id, args.Role)
+	return user{}, err
+}
+
+func (r *Resolver) User(ctx context.Context, args struct{ Id string }) (user, error) {
+	if usr, ok := usersMap[args.Id]; ok {
+		return *usr, nil
+	}
+	err := fmt.Errorf("user with id=%s does not exist", args.Id)
+	return user{}, err
+}
+
+func (r *Resolver) Search(ctx context.Context, args struct{ Text string }) ([]*searchResult, error) {
+	var result []*searchResult
+	for _, usr := range users {
+		if strings.Contains(usr.NameField, args.Text) {
+			result = append(result, &searchResult{usr})
+		}
+	}
+	return result, nil
+}
diff --git a/graphql.go b/graphql.go
@@ -2,9 +2,8 @@ package graphql
 
 import (
 	"context"
-	"fmt"
-
 	"encoding/json"
+	"fmt"
 
 	"github.com/graph-gophers/graphql-go/errors"
 	"github.com/graph-gophers/graphql-go/internal/common"
@@ -84,6 +83,13 @@ func UseStringDescriptions() SchemaOpt {
 	}
 }
 
+// Specifies whether to use struct field resolvers
+func UseFieldResolvers() SchemaOpt {
+	return func(s *Schema) {
+		s.schema.UseFieldResolvers = true
+	}
+}
+
 // MaxDepth specifies the maximum field nesting depth in a query. The default is 0 which disables max depth checking.
 func MaxDepth(n int) SchemaOpt {
 	return func(s *Schema) {

diff --git a/internal/exec/exec.go b/internal/exec/exec.go
@@ -178,24 +178,33 @@ func execFieldSelection(ctx context.Context, r *Request, f *fieldToExec, path *p
 			return errors.Errorf("%s", err) // don't execute any more resolvers if context got cancelled
 		}
 
-		var in []reflect.Value
-		if f.field.HasContext {
-			in = append(in, reflect.ValueOf(traceCtx))
-		}
-		if f.field.ArgsPacker != nil {
-			in = append(in, f.field.PackedArgs)
-		}
-		callOut := f.resolver.Method(f.field.MethodIndex).Call(in)
-		result = callOut[0]
-		if f.field.HasError && !callOut[1].IsNil() {
-			resolverErr := callOut[1].Interface().(error)
-			err := errors.Errorf("%s", resolverErr)
-			err.Path = path.toSlice()
-			err.ResolverError = resolverErr
-			if ex, ok := callOut[1].Interface().(extensionser); ok {
-				err.Extensions = ex.Extensions()
+		res := f.resolver
+		if f.field.UseMethodResolver() {
+			var in []reflect.Value
+			if f.field.HasContext {
+				in = append(in, reflect.ValueOf(traceCtx))
+			}
+			if f.field.ArgsPacker != nil {
+				in = append(in, f.field.PackedArgs)
+			}
+			callOut := res.Method(f.field.MethodIndex).Call(in)
+			result = callOut[0]
+			if f.field.HasError && !callOut[1].IsNil() {
+				resolverErr := callOut[1].Interface().(error)
+				err := errors.Errorf("%s", resolverErr)
+				err.Path = path.toSlice()
+				err.ResolverError = resolverErr
+				if ex, ok := callOut[1].Interface().(extensionser); ok {
+					err.Extensions = ex.Extensions()
+				}
+				return err
+			}
+		} else {
+			// TODO extract out unwrapping ptr logic to a common place
+			if res.Kind() == reflect.Ptr {
+				res = res.Elem()
 			}
-			return err
+			result = res.Field(f.field.FieldIndex)
 		}
 		return nil
 	}()