Update extra fields type definition and plus docs about the feature (#…

…2655)

* Update extra fields type definition and plus docs about the feature

* Update docs

codegen/config/config.go

@@ -323,8 +323,10 @@ func (c *Config) injectTypesFromSchema() error {
 }
 
 type TypeMapEntry struct {
-	Model       StringList                 `yaml:"model"`
-	Fields      map[string]TypeMapField    `yaml:"fields,omitempty"`
+	Model  StringList              `yaml:"model"`
+	Fields map[string]TypeMapField `yaml:"fields,omitempty"`
+
+	// Key is the Go name of the field.
 	ExtraFields map[string]ModelExtraField `yaml:"extraFields,omitempty"`
 }
 
@@ -335,9 +337,29 @@ type TypeMapField struct {
 }
 
 type ModelExtraField struct {
-	Type         string `yaml:"type"`
-	IsPointer    bool   `yaml:"isPointer"`
+	// Type is the Go type of the field.
+	//
+	// It supports the builtin basic types (like string or int64), named types
+	// (qualified by the full package path), pointers to those types (prefixed
+	// with `*`), and slices of those types (prefixed with `[]`).
+	//
+	// For example, the following are valid types:
+	//  string
+	//  *github.com/author/package.Type
+	//  []string
+	//  []*github.com/author/package.Type
+	//
+	// Note that the type will be referenced from the generated/graphql, which
+	// means the package it lives in must not reference the generated/graphql
+	// package to avoid circular imports.
+	// restrictions.
+	Type string `yaml:"type"`
+
+	// OverrideTags is an optional override of the Go field tag.
 	OverrideTags string `yaml:"overrideTags"`
+
+	// Description is an optional the Go field doc-comment.
+	Description string `yaml:"description"`
 }
 
 type StringList []string

docs/content/recipes/extra_fields.md

@@ -0,0 +1,47 @@
+---
+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' } }
+---
+
+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!
+}
+```
+
+Extra fields can be defined in gqlgen.yaml configuration:
+
+```yaml
+models:
+  User:
+    extraFields:
+      Session:
+        description: "A Session used by this user"
+        type: "github.com/author/mypkg.Session"
+```
+
+The generated code would look like:
+
+```go
+// Code generated by github.com/99designs/gqlgen, DO NOT EDIT.
+
+type User struct {
+	ID   string
+	Name string
+	// A Session used by this user.
+	Session mypkg.Session
+}
+```
+
+After these steps you have an extra field for your server implementation and the field is not being exposed to a caller.

plugin/modelgen/models.go

@@ -10,7 +10,6 @@ import (
 
 	"github.com/99designs/gqlgen/codegen/config"
 	"github.com/99designs/gqlgen/codegen/templates"
-	"github.com/99designs/gqlgen/internal/code"
 	"github.com/99designs/gqlgen/plugin"
 	"github.com/vektah/gqlparser/v2/ast"
 )
@@ -415,26 +414,7 @@ func (m *Plugin) generateFields(cfg *config.Config, schemaType *ast.Definition)
 	if len(modelcfg.ExtraFields) > 0 {
 		ff := make([]*Field, 0, len(modelcfg.ExtraFields))
 		for fname, fspec := range modelcfg.ExtraFields {
-			var ftype types.Type
-			pkg, typeName := code.PkgAndType(fspec.Type)
-			if pkg != "" {
-				var err error
-				ftype, err = binder.FindType(pkg, typeName)
-				if err != nil {
-					return nil, fmt.Errorf("extra fields: find type %s.%s: %w", pkg, typeName, err)
-				}
-			} else {
-				// switching to builtin types
-				ftype = types.NewNamed(
-					types.NewTypeName(0, cfg.Model.Pkg(), typeName, nil),
-					nil,
-					nil,
-				)
-			}
-
-			if fspec.IsPointer {
-				ftype = types.NewPointer(ftype)
-			}
+			ftype := buildType(fspec.Type)
 
 			tag := `json:"-"`
 			if fspec.OverrideTags != "" {
@@ -446,7 +426,7 @@ func (m *Plugin) generateFields(cfg *config.Config, schemaType *ast.Definition)
 					Name:        fname,
 					GoName:      fname,
 					Type:        ftype,
-					Description: "User defined extra field",
+					Description: fspec.Description,
 					Tag:         tag,
 				})
 		}

plugin/modelgen/models_test.go

@@ -293,6 +293,7 @@ func TestModelGeneration(t *testing.T) {
 		require.IsType(t, m.FieldInt, int64(0))
 		require.IsType(t, m.FieldInternalType, extrafields.Type{})
 		require.IsType(t, m.FieldStringPtr, new(string))
+		require.IsType(t, m.FieldIntSlice, []int64{})
 	})
 }
 

plugin/modelgen/testdata/gqlgen.yml

@@ -26,10 +26,12 @@ models:
   ExtraFieldsTest:
     extraFields:
       FieldInternalType:
+        description: "Internal field"
         type: github.com/99designs/gqlgen/plugin/modelgen/internal/extrafields.Type
       FieldStringPtr:
-        type: "string"
-        isPointer: true
+        type: "*string"
       FieldInt:
         type: "int64"
         overrideTags: 'json:"field_int_tag"'
+      FieldIntSlice:
+        type: "[]int64"

plugin/modelgen/types.go

@@ -0,0 +1,47 @@
+package modelgen
+
+import (
+	"go/types"
+	"strings"
+)
+
+// buildType constructs a types.Type for the given string (using the syntax
+// from the extra field config Type field).
+func buildType(typeString string) types.Type {
+	switch {
+	case typeString[0] == '*':
+		return types.NewPointer(buildType(typeString[1:]))
+	case strings.HasPrefix(typeString, "[]"):
+		return types.NewSlice(buildType(typeString[2:]))
+	default:
+		return buildNamedType(typeString)
+	}
+}
+
+// buildNamedType returns the specified named or builtin type.
+//
+// Note that we don't look up the full types.Type object from the appropriate
+// package -- gqlgen doesn't give us the package-map we'd need to do so.
+// Instead we construct a placeholder type that has all the fields gqlgen
+// wants. This is roughly what gqlgen itself does, anyway:
+// https://github.com/99designs/gqlgen/blob/master/plugin/modelgen/models.go#L119
+func buildNamedType(fullName string) types.Type {
+	dotIndex := strings.LastIndex(fullName, ".")
+	if dotIndex == -1 { // builtinType
+		return types.Universe.Lookup(fullName).Type()
+	}
+
+	// type is pkg.Name
+	pkgPath := fullName[:dotIndex]
+	typeName := fullName[dotIndex+1:]
+
+	pkgName := pkgPath
+	slashIndex := strings.LastIndex(pkgPath, "/")
+	if slashIndex != -1 {
+		pkgName = pkgPath[slashIndex+1:]
+	}
+
+	pkg := types.NewPackage(pkgPath, pkgName)
+	// gqlgen doesn't use some of the fields, so we leave them 0/nil
+	return types.NewNamed(types.NewTypeName(0, pkg, typeName, nil), nil, nil)
+}