Add ability to customize resolvergen behavior using additional plugins

api/generate.go

@@ -83,7 +83,11 @@ func Generate(cfg *config.Config, option ...Option) error {
 		}
 	}
 	// Merge again now that the generated models have been injected into the typemap
-	data, err := codegen.BuildData(cfg)
+	data_plugins := make([]interface{}, len(plugins))
+	for index := range plugins {
+		data_plugins[index] = plugins[index]
+	}
+	data, err := codegen.BuildData(cfg, data_plugins...)
 	if err != nil {
 		return fmt.Errorf("merging type systems failed: %w", err)
 	}

codegen/data.go

@@ -34,6 +34,7 @@ type Data struct {
 	MutationRoot     *Object
 	SubscriptionRoot *Object
 	AugmentedSources []AugmentedSource
+	Plugins          []interface{}
 }
 
 func (d *Data) HasEmbeddableSources() bool {
@@ -76,7 +77,7 @@ func (d *Data) Directives() DirectiveList {
 	return res
 }
 
-func BuildData(cfg *config.Config) (*Data, error) {
+func BuildData(cfg *config.Config, plugins ...interface{}) (*Data, error) {
 	// We reload all packages to allow packages to be compared correctly.
 	cfg.ReloadAllPackages()
 
@@ -105,6 +106,7 @@ func BuildData(cfg *config.Config) (*Data, error) {
 		AllDirectives: dataDirectives,
 		Schema:        b.Schema,
 		Interfaces:    map[string]*Interface{},
+		Plugins:       plugins,
 	}
 
 	for _, schemaType := range b.Schema.Types {

codegen/field.go

@@ -503,6 +503,14 @@ func (f *Field) ResolverType() string {
 	return fmt.Sprintf("%s().%s(%s)", f.Object.Definition.Name, f.GoFieldName, f.CallArgs())
 }
 
+func (f *Field) IsInputObject() bool {
+	return f.Object.Kind == ast.InputObject
+}
+
+func (f *Field) IsRoot() bool {
+	return f.Object.Root
+}
+
 func (f *Field) ShortResolverDeclaration() string {
 	return f.ShortResolverSignature(nil)
 }
@@ -544,6 +552,13 @@ func (f *Field) ShortResolverSignature(ft *goast.FuncType) string {
 	return res
 }
 
+func (f *Field) GoResultName() (string, bool) {
+	name := fmt.Sprintf("%v", f.TypeReference.GO)
+	splits := strings.Split(name, "/")
+
+	return splits[len(splits)-1], strings.HasPrefix(name, "[]")
+}
+
 func (f *Field) ComplexitySignature() string {
 	res := "func(childComplexity int"
 	for _, arg := range f.Args {

codegen/object.go

@@ -153,6 +153,16 @@ func (o *Object) Description() string {
 	return o.Definition.Description
 }
 
+func (o *Object) HasField(name string) bool {
+	for _, f := range o.Fields {
+		if f.Name == name {
+			return true
+		}
+	}
+
+	return false
+}
+
 func (os Objects) ByName(name string) *Object {
 	for i, o := range os {
 		if strings.EqualFold(o.Definition.Name, name) {

plugin/plugin.go

@@ -29,3 +29,8 @@ type EarlySourceInjector interface {
 type LateSourceInjector interface {
 	InjectSourceLate(schema *ast.Schema) *ast.Source
 }
+
+// Implementer is used to generate code inside resolvers
+type ResolverImplementer interface {
+	Implement(field *codegen.Field) string
+}

plugin/resolvergen/resolver.go

@@ -121,12 +121,29 @@ func (m *Plugin) generatePerSchema(data *codegen.Data) error {
 
 			structName := templates.LcFirst(o.Name) + templates.UcFirst(data.Config.Resolver.Type)
 			comment := strings.TrimSpace(strings.TrimLeft(rewriter.GetMethodComment(structName, f.GoFieldName), `\`))
+
 			if comment == "" {
 				comment = fmt.Sprintf("%v is the resolver for the %v field.", f.GoFieldName, f.Name)
 			}
 			implementation := strings.TrimSpace(rewriter.GetMethodBody(structName, f.GoFieldName))
 			if implementation == "" {
-				implementation = fmt.Sprintf("panic(fmt.Errorf(\"not implemented: %v - %v\"))", f.GoFieldName, f.Name)
+				// Check for Implementer Plugin
+				var resolver_implementer plugin.ResolverImplementer
+				var exists bool
+				for _, p := range data.Plugins {
+					if p_cast, ok := p.(plugin.ResolverImplementer); ok {
+						resolver_implementer = p_cast
+						exists = true
+						break
+					}
+				}
+
+				if exists {
+					implementation = resolver_implementer.Implement(f)
+				} else {
+					implementation = fmt.Sprintf("panic(fmt.Errorf(\"not implemented: %v - %v\"))", f.GoFieldName, f.Name)
+				}
+
 			}
 
 			resolver := Resolver{o, f, rewriter.GetPrevDecl(structName, f.GoFieldName), comment, implementation}