How to define an optional field in protobuf 3

by

Since protobuf release 3.15, proto3 supports using the optional keyword (just as in proto2) to give a scalar field presence information.

syntax = "proto3";

message Foo {
    int32 bar = 1;
    optional int32 baz = 2;
}

A has_baz()/hasBaz() method is generated for the optional field above, just as it was in proto2.

Under the hood, protoc effectively treats an optional field as if it were declared using a oneof wrapper, as CyberSnoopy’s answer suggested:

message Foo {
    int32 bar = 1;
    oneof optional_baz {
        int32 baz = 2;
    }
}

If you’ve already used that approach, you can now simplify your message declarations (switch from oneof to optional) and code, since the wire format is the same.

The nitty-gritty details about field presence and optional in proto3 can be found in the Application note: Field presence doc.

Historical note: Experimental support for optional in proto3 was first announced on Apr 23, 2020 in this comment. Using it required passing protoc the --experimental_allow_proto3_optional flag in releases 3.12-3.14.

More Related Contents:

  1. Why required and optional is removed in Protocol Buffers 3
  2. raw decoder for protobufs format
  3. Getting Segmentation fault for implementing ByteSize() in C++ for protobuffer
  4. Are there C++ equivalents for the Protocol Buffers delimited I/O functions in Java?
  5. InfogainLoss layer
  6. What does the protobuf text format look like?
  7. Google Protocol Buffers: JavaScript Example
  8. How to build Google’s protobuf in Windows using MinGW?
  9. TensorFlow saving into/loading a graph from a file
  10. Errors when linking to protobuf 3 on MS Visual C
  11. Retrieve large blob from Android sqlite database
  12. protoc-gen-go-grpc: program not found or is not executable
  13. Biggest differences of Thrift vs Protocol Buffers? [closed]
  14. Undefined reference to google::protobuf::internal::empty_string_[abi:cxx11]
  15. How to create GRPC client directly from protobuf without compiling it into java code
  16. How to solve “AttributeError: module ‘google.protobuf.descriptor’ has no attribute ‘_internal_create_key”?
  17. C++ Serialization Performance
  18. What’s the best way to represent System.Decimal in Protocol Buffers?

Leave a Comment