Make the resolver implementation configurable via a new template resolver.gotpl

codegen/config/resolver.go

@@ -17,6 +17,7 @@ type ResolverConfig struct {
 	Layout              ResolverLayout `yaml:"layout,omitempty"`
 	DirName             string         `yaml:"dir"`
 	OmitTemplateComment bool           `yaml:"omit_template_comment,omitempty"`
+	ResolverTemplate    string         `yaml:"resolver_template,omitempty"`
 }
 
 type ResolverLayout string

docs/content/config.md

@@ -39,6 +39,8 @@ resolver:
   filename_template: "{name}.resolvers.go"
   # Optional: turn on to not generate template comments above resolvers
   # omit_template_comment: false
+  # Optional: Pass in a path to a new gotpl template to use for generating resolvers
+  # resolver_template: [your/path/resolver.gotpl]
 
 # Optional: turn on use ` + "`" + `gqlgen:"fieldName"` + "`" + ` tags in your models
 # struct_tag: json

plugin/resolvergen/resolver.go

@@ -81,6 +81,10 @@ func (m *Plugin) generateSingleFile(data *codegen.Data) error {
 		OmitTemplateComment: data.Config.Resolver.OmitTemplateComment,
 	}
 
+	if data.Config.Resolver.ResolverTemplate != "" {
+		resolverTemplate = readResolverTemplate(data.Config.Resolver.ResolverTemplate)
+	}
+
 	return templates.Render(templates.Options{
 		PackageName: data.Config.Resolver.Package,
 		FileNotice:  `// THIS CODE IS A STARTING POINT ONLY. IT WILL NOT BE UPDATED WITH SCHEMA CHANGES.`,
@@ -159,6 +163,10 @@ func (m *Plugin) generatePerSchema(data *codegen.Data) error {
 		file.RemainingSource = rewriter.RemainingSource(filename)
 	}
 
+	if data.Config.Resolver.ResolverTemplate != "" {
+		resolverTemplate = readResolverTemplate(data.Config.Resolver.ResolverTemplate)
+	}
+
 	for filename, file := range files {
 		resolverBuild := &ResolverBuild{
 			File:                file,
@@ -257,3 +265,11 @@ func gqlToResolverName(base string, gqlname, filenameTmpl string) string {
 	filename := strings.ReplaceAll(filenameTmpl, "{name}", strings.TrimSuffix(gqlname, ext))
 	return filepath.Join(base, filename)
 }
+
+func readResolverTemplate(customResolverTemplate string) string {
+	contentBytes, err := os.ReadFile(customResolverTemplate)
+	if err != nil {
+		panic(err)
+	}
+	return string(contentBytes)
+}

plugin/resolvergen/resolver_test.go

@@ -83,6 +83,22 @@ func TestOmitTemplateComment(t *testing.T) {
 	assertNoErrors(t, "github.com/99designs/gqlgen/plugin/resolvergen/testdata/omit_template_comment/out")
 }
 
+func TestCustomResolverTemplate(t *testing.T) {
+	_ = syscall.Unlink("testdata/resolvertemplate/out/resolver.go")
+	cfg, err := config.LoadConfig("testdata/resolvertemplate/gqlgen.yml")
+	require.NoError(t, err)
+	p := Plugin{}
+
+	require.NoError(t, cfg.Init())
+
+	data, err := codegen.BuildData(cfg)
+	if err != nil {
+		panic(err)
+	}
+
+	require.NoError(t, p.GenerateCode(data))
+}
+
 func testFollowSchemaPersistence(t *testing.T, dir string) {
 	_ = syscall.Unlink(dir + "/out/resolver.go")
 

plugin/resolvergen/testdata/resolvertemplate/customResolverTemplate.gotpl

@@ -0,0 +1,54 @@
+{{ reserveImport "context"  }}
+{{ reserveImport "fmt"  }}
+{{ reserveImport "io"  }}
+{{ reserveImport "strconv"  }}
+{{ reserveImport "time"  }}
+{{ reserveImport "sync"  }}
+{{ reserveImport "errors"  }}
+{{ reserveImport "bytes"  }}
+{{ reserveImport "encoding/json"  }}
+
+{{ reserveImport "github.com/vektah/gqlparser/v2" }}
+{{ reserveImport "github.com/vektah/gqlparser/v2/ast" }}
+{{ reserveImport "github.com/99designs/gqlgen/graphql" }}
+{{ reserveImport "github.com/99designs/gqlgen/graphql/introspection" }}
+
+{{ .Imports }}
+
+{{ if .HasRoot }}
+	type {{.ResolverType}} struct {}
+{{ end }}
+
+{{ range $resolver := .Resolvers -}}
+	{{ if $resolver.Comment -}}
+		// {{ $resolver.Comment }}
+	{{- else if not $.OmitTemplateComment -}}
+		// {{ $resolver.Field.GoFieldName }} is the resolver for the {{ $resolver.Field.Name }} field.
+	{{- end }}
+	func (r *{{lcFirst $resolver.Object.Name}}{{ucFirst $.ResolverType}}) {{$resolver.Field.GoFieldName}}{{ with $resolver.PrevDecl }}{{ $resolver.Field.ShortResolverSignature .Type }}{{ else }}{{ $resolver.Field.ShortResolverDeclaration }}{{ end }}{
+		// Custom Resolver implementation
+		panic(fmt.Errorf("custom Resolver not implemented: {{ $resolver.Field.GoFieldName }} - {{lcFirst $resolver.Field.GoFieldName }}"))
+	}
+
+{{ end }}
+
+{{ range $object := .Objects -}}
+	{{ if not $.OmitTemplateComment -}}
+		// {{ucFirst $object.Name}} returns {{ $object.ResolverInterface | ref }} implementation.
+	{{- end }}
+	func (r *{{$.ResolverType}}) {{ucFirst $object.Name}}() {{ $object.ResolverInterface | ref }} { return &{{lcFirst $object.Name}}{{ucFirst $.ResolverType}}{r} }
+{{ end }}
+
+{{ range $object := .Objects -}}
+	type {{lcFirst $object.Name}}{{ucFirst $.ResolverType}} struct { *{{$.ResolverType}} }
+{{ end }}
+
+{{ if (ne .RemainingSource "") }}
+    // !!! WARNING !!!
+    // The code below was going to be deleted when updating resolvers. It has been copied here so you have
+    // one last chance to move it out of harms way if you want. There are two reasons this happens:
+	//  - When renaming or deleting a resolver the old code will be put in here. You can safely delete
+	//    it when you're done.
+	//  - You have helper methods in this file. Move them out to keep these resolver files clean.
+	{{ .RemainingSource }}
+{{ end }}

plugin/resolvergen/testdata/resolvertemplate/gqlgen.yml

@@ -0,0 +1,17 @@
+schema:
+  - "testdata/schema.graphql"
+
+exec:
+  filename: testdata/singlefile/out/ignored.go
+model:
+  filename: testdata/singlefile/out/generated.go
+resolver:
+  type: CustomResolverType
+  layout: follow-schema
+  dir: testdata/resolvertemplate/out
+  filename_template: "{name}.resolvers.go"
+  resolver_template: "testdata/resolvertemplate/customResolverTemplate.gotpl"
+
+models:
+  Resolver:
+    model: github.com/99designs/gqlgen/plugin/resolvergen/testdata/singlefile/out.Resolver

plugin/resolvergen/testdata/resolvertemplate/out/resolver.go

@@ -0,0 +1,7 @@
+package out
+
+// This file will not be regenerated automatically.
+//
+// It serves as dependency injection for your app, add any dependencies you require here.
+
+type CustomResolverType struct{}