Nullable fields in json generated from protobuf file

• 06, 15, 2021
•  bullgare
•  golang
• No Comments.

Native support

With grpc v2 for go, protofile’s optional option is supported, so you don’t need to import proto extensions anymore and use things like google.protobuf.StringValue.

my.proto

message FeeView {
    optional string name = 1 [json_name = "name"];
}

go mapper

var name *string
if fee.Name != nil {
	name = &fee.Name
}

fee := &desc.FeeView{
	Name: name,
}

Legacy way with extensions

Null for nil value

my.proto

import "google/protobuf/wrappers.proto";

message FeeView {
    google.protobuf.StringValue name = 1 [json_name = "name"];
}

go mapper

import "github.com/gogo/protobuf/types"

var name *types.StringValue
if fee.Name != nil {
	name = &types.StringValue{
		Value: *fee.Name,
	}
}

fee := &desc.FeeView{
	Name: name,
}

Which will lead to this json response

{"translation_key":"a fee","name":null,"value":5,"style":"body","text_color":"grey","tag":null}

Omit a field with nil value

If you want to omit the field completely, you can use oneof approach

proto

message View {
    oneof subtitle {
        string oneof_string_subtitle = 1 [json_name = "subtitle"];
    }
}

go mapper

var subtitle *desc.View_OneofStringSubtitle
if in.Subtitle != nil {
	subtitle = &desc.View_OneofStringSubtitle{
		OneofStringSubtitle: *in.Subtitle,
	}
}

return &desc.View{
	Subtitle: subtitle,
}

More info on json options for grpc — https://blog.bullgare.com/2020/07/complete-list-of-swagger-options-to-protobuf-file/