kratos-mapper

---

name: kratos-mapper description: Generates bidirectional mapper functions (transformers/converters/adapters) between protobuf DTOs and business domain models for go-kratos services. Creates type-safe conversions with proper field mapping, handles timestamps, enums, optional fields, and pagination metadata transformations. Use when converting DTOs to domain models, transforming proto to biz models, mapping requests/responses, implementing type conversions, creating entity transformers, or handling DTO transformations between layers. tags: [kratos, mapper, dto, converter, transformer, proto, domain-model, type-conversion] keywords: [mapper, convert, transform, DTO, proto to domain, domain to proto, type conversion, request mapping, response mapping, transformer, converter, adapter] version: 2.0.0 last_updated: 2026-01-12

<quick_start> For an entity, create mappers in internal/service/mapper.go:

Copy// Request → Business Model
func {Entity}FromCreateRequest(req *pb.Create{Entity}Request) *domain.{Entity} {
	return &domain.{Entity}{
		Name: req.Name,
		// Map fields...
	}
}

// Business Model → Proto Response
func toProto{Entity}(e *domain.{Entity}) *pb.{Entity} {
	return &pb.{Entity}{
		Id:   e.ID,
		Name: e.Name,
		// Map fields...
	}
}

**Import**: `import "{service}/internal/biz/domain"`

</quick_start>

<mapper_patterns>

Common Mapper Patterns

Request to Business Model:

Copyfunc {Entity}FromCreateRequest(req *pb.Create{Entity}Request) *domain.{Entity}
func {Entity}FromUpdateRequest(req *pb.Update{Entity}Request, id uint64) *domain.{Entity}

Business Model to Proto:

Copyfunc toProto{Entity}(e *domain.{Entity}) *pb.{Entity}
func toProto{Entities}(list []*domain.{Entity}) []*pb.{Entity}

List Options:

Copyfunc NewList{Entities}Options(req *pb.List{Entities}Request) *domain.List{Entities}Options {
	return &domain.List{Entities}Options{
		Pagination: pagination.OffsetPaginationParams{
			Offset: req.Offset,
			Limit:  req.Limit,
		},
	}
}

Pagination Meta:

Copyfunc toProtoPaginationMeta(meta *pagination.PaginationMeta) *pb.PaginationMeta {
	return &pb.PaginationMeta{
		Total:  meta.Total,
		Offset: meta.Offset,
		Limit:  meta.Limit,
	}
}

</mapper_patterns>

<naming_conventions>

Naming Rules

Proto → Business: {Entity}From{Operation}Request

• Example: SymbolFromCreateRequest, ProductFromUpdateRequest

Business → Proto: toProto{Entity} or toProto{Entities}

• Example: toProtoSymbol, toProtoSymbols

Options: NewList{Entities}Options

Helpers: toProto{Type} for common types

• Example: toProtoPaginationMeta, toProtoTimestamp </naming_conventions>

<type_conversions>

Common Type Conversions

IDs: uint64 ↔ uint64 (direct) Strings: string ↔ string (direct) Timestamps: time.Time ↔ *timestamppb.Timestamp

CopyCreatedAt: timestamppb.New(e.CreatedAt)

Optional Fields: Use pointers

Copy// Business has *string, proto has string
Email: func() string {
	if e.Email != nil {
		return *e.Email
	}
	return ""
}()

Enums: Map string to proto enum

CopyStatus: pb.Status(pb.Status_value[e.Status])

</type_conversions>

<file_organization>

Where to Put Mappers

Single entity: internal/service/mapper.go (all mappers) Multiple entities: internal/service/{entity}_mapper.go (per entity)

Keep mapper functions close to service handlers for easy reference. </file_organization>

<success_criteria> Mapper functions are correct when:

• Naming follows conventions ({Entity}From* vs toProto*)
• All proto fields mapped to business model fields
• Type conversions handled (timestamps, optionals, enums)
• Nil checks for optional/pointer fields
• List mappers use range loops
• Pagination helpers created if needed
• Functions are pure (no side effects) </success_criteria>