From 8850a527a89f9b880531dc7fdcfec1016882b777 Mon Sep 17 00:00:00 2001
From: Adam <adam@vektah.net>
Date: Fri, 7 Feb 2020 08:33:36 +1100
Subject: [PATCH] Create a non generated federation _Entity type

---
 plugin/federation/federation.go         | 14 ++++++--------
 plugin/federation/federation.gotpl      | 12 ++++++------
 plugin/federation/fedruntime/runtime.go | 13 +++++++++++++
 plugin/modelgen/models.go               |  8 --------
 4 files changed, 25 insertions(+), 22 deletions(-)
 create mode 100644 plugin/federation/fedruntime/runtime.go

diff --git a/plugin/federation/federation.go b/plugin/federation/federation.go
index fe7bb2ebf3..cca7a358a6 100644
--- a/plugin/federation/federation.go
+++ b/plugin/federation/federation.go
@@ -50,7 +50,12 @@ func (f *federation) MutateConfig(cfg *config.Config) error {
 	builtins := config.TypeMap{
 		"_Service": {
 			Model: config.StringList{
-				"github.com/99designs/gqlgen/plugin/federation.Service",
+				"github.com/99designs/gqlgen/plugin/federation/fedruntime.Service",
+			},
+		},
+		"_Entity": {
+			Model: config.StringList{
+				"github.com/99designs/gqlgen/plugin/federation/fedruntime.Entity",
 			},
 		},
 		"_Any": {
@@ -361,10 +366,3 @@ func (f *federation) getSDL(c *config.Config) (string, error) {
 	formatter.NewFormatter(&buf).FormatSchema(schema)
 	return buf.String(), nil
 }
-
-// Service is the service object that the
-// generated.go file will return for the _service
-// query
-type Service struct {
-	SDL string `json:"sdl"`
-}
diff --git a/plugin/federation/federation.gotpl b/plugin/federation/federation.gotpl
index 3672b0b84c..9fab3f04f0 100644
--- a/plugin/federation/federation.gotpl
+++ b/plugin/federation/federation.gotpl
@@ -2,20 +2,20 @@
 {{ reserveImport "errors"  }}
 {{ reserveImport "fmt"  }}
 
-{{ reserveImport "github.com/99designs/gqlgen/plugin/federation" }}
+{{ reserveImport "github.com/99designs/gqlgen/plugin/federation/fedruntime" }}
 
-func (ec *executionContext) __resolve__service(ctx context.Context) (federation.Service, error) {
+func (ec *executionContext) __resolve__service(ctx context.Context) (fedruntime.Service, error) {
 	if ec.DisableIntrospection {
-		return federation.Service{}, errors.New("federated introspection disabled")
+		return fedruntime.Service{}, errors.New("federated introspection disabled")
 	}
-	return federation.Service{
+	return fedruntime.Service{
 		SDL: `{{.SDL}}`,
 	}, nil
 }
 
 {{if .Entities}}
-func (ec *executionContext) __resolve_entities(ctx context.Context, representations []map[string]interface{}) ([]_Entity, error) {
-	list := []_Entity{}
+func (ec *executionContext) __resolve_entities(ctx context.Context, representations []map[string]interface{}) ([]fedruntime.Entity, error) {
+	list := []fedruntime.Entity{}
 	for _, rep := range representations {
 		typeName, ok := rep["__typename"].(string)
 		if !ok {
diff --git a/plugin/federation/fedruntime/runtime.go b/plugin/federation/fedruntime/runtime.go
new file mode 100644
index 0000000000..43a924404a
--- /dev/null
+++ b/plugin/federation/fedruntime/runtime.go
@@ -0,0 +1,13 @@
+package fedruntime
+
+// Service is the service object that the
+// generated.go file will return for the _service
+// query
+type Service struct {
+	SDL string `json:"sdl"`
+}
+
+// Everything with a @key implements this
+type Entity interface {
+	Is_Entity()
+}
diff --git a/plugin/modelgen/models.go b/plugin/modelgen/models.go
index 4f86a52f91..afcf65d69a 100644
--- a/plugin/modelgen/models.go
+++ b/plugin/modelgen/models.go
@@ -83,11 +83,6 @@ func (m *Plugin) MutateConfig(cfg *config.Config) error {
 		if cfg.Models.UserDefined(schemaType.Name) {
 			continue
 		}
-		ent := false
-		if schemaType.Directives.ForName("key") != nil {
-			hasEntity = true
-			ent = true
-		}
 		switch schemaType.Kind {
 		case ast.Interface, ast.Union:
 			it := &Interface{
@@ -108,9 +103,6 @@ func (m *Plugin) MutateConfig(cfg *config.Config) error {
 				it.Implements = append(it.Implements, implementor.Name)
 			}
 
-			if ent { // only when Object. Directive validation should have occurred on InputObject otherwise.
-				it.Implements = append(it.Implements, "_Entity")
-			}
 			for _, field := range schemaType.Fields {
 				var typ types.Type
 				fieldDef := cfg.Schema.Types[field.Type.Name()]