Separate resolvers for each operation

README.md

@@ -97,6 +97,50 @@ func (r *helloWorldResolver) Hello(ctx context.Context) (string, error) {
 }
 ```
 
+### Separate resolvers for different operations
+
+The GraphQL specification allows for fields with the same name defined in different query types. For example, the schema below is a valid schema definition:
+```graphql
+schema {
+  query: Query
+  mutation: Mutation
+}
+
+type Query {
+  hello: String!
+}
+
+type Mutation {
+  hello: String!
+}
+```
+The above schema would result in name collision if we use a single resolver struct because fields from both operations correspond to methods in the root resolver (the same Go struct). In order to resolve this issue, the library allows resolvers for query, mutation and subscription operations to be separated using the `Query`, `Mutation` and `Subscription` methods of the root resolver. These special methods are optional and if defined return the resolver for each opeartion. For example, the following is a resolver corresponding to the schema definition above. Note that there is a field named `hello` in both the query and the mutation definitions:
+
+```go
+type RootResolver struct{}
+type QueryResolver struct{}
+type MutationResolver struct{}
+
+func(r *RootResolver) Query() *QueryResolver {
+  return &QueryResolver{}
+}
+
+func(r *RootResolver) Mutation() *MutationResolver {
+  return &MutationResolver{}
+}
+
+func (*QueryResolver) Hello() string {
+	return "Hello query!"
+}
+
+func (*MutationResolver) Hello() string {
+	return "Hello mutation!"
+}
+
+schema := graphql.MustParseSchema(sdl, &RootResolver{}, nil)
+...
+```
+
 ### Schema Options
 
 - `UseStringDescriptions()` enables the usage of double quoted and triple quoted. When this is not enabled, comments are parsed as descriptions instead.

example/starwars/starwars.go

@@ -286,22 +286,28 @@ var reviews = make(map[string][]*review)
 
 type Resolver struct{}
 
-func (r *Resolver) Hero(args struct{ Episode string }) *characterResolver {
+func (*Resolver) Query() *QueryResolver {
+	return &QueryResolver{}
+}
+
+type QueryResolver struct{}
+
+func (r *QueryResolver) Hero(args struct{ Episode string }) *characterResolver {
 	if args.Episode == "EMPIRE" {
 		return &characterResolver{&humanResolver{humanData["1000"]}}
 	}
 	return &characterResolver{&droidResolver{droidData["2001"]}}
 }
 
-func (r *Resolver) Reviews(args struct{ Episode string }) []*reviewResolver {
+func (r *QueryResolver) Reviews(args struct{ Episode string }) []*reviewResolver {
 	var l []*reviewResolver
 	for _, review := range reviews[args.Episode] {
 		l = append(l, &reviewResolver{review})
 	}
 	return l
 }
 
-func (r *Resolver) Search(args struct{ Text string }) []*searchResultResolver {
+func (r *QueryResolver) Search(args struct{ Text string }) []*searchResultResolver {
 	var l []*searchResultResolver
 	for _, h := range humans {
 		if strings.Contains(h.Name, args.Text) {
@@ -321,7 +327,7 @@ func (r *Resolver) Search(args struct{ Text string }) []*searchResultResolver {
 	return l
 }
 
-func (r *Resolver) Character(args struct{ ID graphql.ID }) *characterResolver {
+func (r *QueryResolver) Character(args struct{ ID graphql.ID }) *characterResolver {
 	if h := humanData[args.ID]; h != nil {
 		return &characterResolver{&humanResolver{h}}
 	}
@@ -331,28 +337,34 @@ func (r *Resolver) Character(args struct{ ID graphql.ID }) *characterResolver {
 	return nil
 }
 
-func (r *Resolver) Human(args struct{ ID graphql.ID }) *humanResolver {
+func (r *QueryResolver) Human(args struct{ ID graphql.ID }) *humanResolver {
 	if h := humanData[args.ID]; h != nil {
 		return &humanResolver{h}
 	}
 	return nil
 }
 
-func (r *Resolver) Droid(args struct{ ID graphql.ID }) *droidResolver {
+func (r *QueryResolver) Droid(args struct{ ID graphql.ID }) *droidResolver {
 	if d := droidData[args.ID]; d != nil {
 		return &droidResolver{d}
 	}
 	return nil
 }
 
-func (r *Resolver) Starship(args struct{ ID graphql.ID }) *starshipResolver {
+func (r *QueryResolver) Starship(args struct{ ID graphql.ID }) *starshipResolver {
 	if s := starshipData[args.ID]; s != nil {
 		return &starshipResolver{s}
 	}
 	return nil
 }
 
-func (r *Resolver) CreateReview(args *struct {
+func (*Resolver) Mutation() *MutationResolver {
+	return &MutationResolver{}
+}
+
+type MutationResolver struct{}
+
+func (r *MutationResolver) CreateReview(args *struct {
 	Episode string
 	Review  *reviewInput
 }) *reviewResolver {

graphql.go

@@ -247,7 +247,7 @@ func (s *Schema) ValidateWithVariables(queryString string, variables map[string]
 // without a resolver. If the context get cancelled, no further resolvers will be called and a
 // the context error will be returned as soon as possible (not immediately).
 func (s *Schema) Exec(ctx context.Context, queryString string, operationName string, variables map[string]interface{}) *Response {
-	if !s.res.Resolver.IsValid() {
+	if !s.res.QueryResolver.IsValid() {
 		panic("schema created without resolver, can not exec")
 	}
 	execF := s.exec