Ability to inline extraFields configuration. New @goExtraField direct…

…ive. (#3076)

* @goExtraField directive added

* docs for @goExtraField added

---------

Co-authored-by: Roman A. Grigorovich <ragrigorov@mts.ru>

codegen/config/config.go

@@ -275,6 +275,10 @@ func (c *Config) injectTypesFromSchema() error {
 		SkipRuntime: true,
 	}
 
+	c.Directives["goExtraField"] = DirectiveConfig{
+		SkipRuntime: true,
+	}
+
 	c.Directives["goField"] = DirectiveConfig{
 		SkipRuntime: true,
 	}
@@ -346,6 +350,43 @@ func (c *Config) injectTypesFromSchema() error {
 					}
 				}
 			}
+
+			if efds := schemaType.Directives.ForNames("goExtraField"); len(efds) != 0 {
+				for _, efd := range efds {
+					if fn := efd.Arguments.ForName("name"); fn != nil {
+						extraFieldName := ""
+						extraField := ModelExtraField{}
+						if fnv, err := fn.Value.Value(nil); err == nil {
+							if !c.Models.Exists(schemaType.Name) {
+								c.Models[schemaType.Name] = TypeMapEntry{
+									ExtraFields: make(map[string]ModelExtraField),
+								}
+							}
+							extraFieldName = fnv.(string)
+						}
+
+						if t := efd.Arguments.ForName("type"); t != nil {
+							if tv, err := t.Value.Value(nil); err == nil {
+								extraField.Type = tv.(string)
+							}
+						}
+
+						if ot := efd.Arguments.ForName("overrideTags"); ot != nil {
+							if otv, err := ot.Value.Value(nil); err == nil {
+								extraField.OverrideTags = otv.(string)
+							}
+						}
+
+						if d := efd.Arguments.ForName("description"); d != nil {
+							if dv, err := d.Value.Value(nil); err == nil {
+								extraField.Description = dv.(string)
+							}
+						}
+
+						c.Models[schemaType.Name].ExtraFields[extraFieldName] = extraField
+					}
+				}
+			}
 		}
 
 		if schemaType.Kind == ast.Enum && !strings.HasPrefix(schemaType.Name, "__") {

docs/content/recipes/extra_fields.md

@@ -2,21 +2,22 @@
 title: "Generation of additional extra fields for internal use"
 description: Pass implementation specific fields to the children resolvers without being forced to define your own types for a GraphQL model.
 linkTitle: Generated Model Extra Fields
-menu: { main: { parent: 'recipes' } }
+menu: { main: { parent: "recipes" } }
 ---
 
 Extra fields allows you to generate additional fields for your models.
 These fields can be used at runtime when implementing field resolvers.
 
 ## Extending your models
+
 Imagine you have a model named User and you want to extend a generated struct with additional data used in your service.
 
 The schema is:
 
 ```graphql
 type User {
-  id: ID!
-  name: String!
+	id: ID!
+	name: String!
 }
 ```
 
@@ -29,6 +30,7 @@ models:
       Session:
         description: "A Session used by this user"
         type: "github.com/author/mypkg.Session"
+        overrideTags: 'xml:"session"'
 ```
 
 The generated code would look like:
@@ -40,8 +42,49 @@ type User struct {
 	ID   string
 	Name string
 	// A Session used by this user.
-	Session mypkg.Session
+	Session mypkg.Session `xml:"session"`
 }
 ```
 
 After these steps you have an extra field for your server implementation and the field is not being exposed to a caller.
+
+### Inline config with directive
+
+To start using it you first need to define it:
+
+```graphql
+directive @goExtraField(
+	name: String!
+	type: String!
+	overrideTags: String
+	description: String
+) on OBJECT | INPUT_OBJECT
+```
+
+Now you can use these directive when defining types in your schema:
+
+```graphql
+type User
+	@goExtraField(
+		name: "Session"
+		type: "github.com/author/mypkg.Session"
+		description: "A Session used by this user"
+		overrideTags: "xml:\"session\""
+	)
+	@goExtraField(name: "Activated", type: "bool") {
+	id: ID
+	name: String
+}
+```
+
+The generated code would look like:
+
+```go
+type User struct {
+  ID   string
+  Name string
+  // A Session used by this user.
+  Session   mypkg.Session `xml:"session"`
+  Activated bool
+}
+```