Add an option to wrap primitives to Option[]

[onsails]

In some cases zeros does not make sence. For example, I have a model Event, stored in relational database:

message Event {
  bytes data = 1;
  int64 deleted_at = 5 [(scalapb.field).type = "org.joda.time.DateTime"];
}

In the past Event did not have a deleted_at, but it had a boolean is_deleted. When deleted_at appeared, it had been set to the epoch start for every deleted event and to NULL for the rest. So, if deleted_at is not an Option, there is no way to determine if event was deleted.

[thesamet]

Two options:

Option A:

int64 deleted_at = 5 [(scalapb.field).type = "Option[org.joda.time.DateTime]"];

and define a TypeMapper[Int, Option[org.joda.time.DateTime]] that maps 0 to None.

Option B:

you can define:

message NullableTime {
  int64 timestamp = 1
}

message Event {
  bytes data = 1;
  NullableTime deleted_at = 5 [(scalapb.field).type = "org.joda.time.DateTime"];
}

Message fields are always in options, and you can then use a custom type for it.

[onsails]

I like NullableTime idea, thanks. It totally covers my case.

[zackangelo]

@thesamet What's the reasoning behind not using Option for optional types in messages? Is it something related to how protobuf messages are encoded (e.g., they can't convey absent values)?

[thesamet]

Exactly. The receiving end has no way of telling if an int32 field was assigned to zero or whether it has not been assigned. See note here: https://developers.google.com/protocol-buffers/docs/proto3?hl=en#default

[zackangelo]

@thesamet this seems like a pretty big regression compared to proto2, am I missing something? :)

[zackangelo]

@thesamet it looks like proto3 betas will include built-in nullable primitives: protocolbuffers/protobuf#159 (comment).

Could we map these to Option types in the generated code?

That being said, I can't find any trace of them in the repo yet.

[zackangelo]

Found them: https://github.com/google/protobuf/blob/master/src/google/protobuf/wrappers.proto

[zackangelo]

Trying to use these built-in wrapped types results in compile-time errors:

[error] /Users/zack.angelo/git/galaxy/interfaces/target/scala-2.11/src_managed/main/compiled_protobuf/com/bigcommerce/services/catalog/Product.scala:37: value serializedSize is not a member of com.google.protobuf.Int32Value

[error]       if (id.isDefined) { __size += 1 + com.google.protobuf.CodedOutputStream.computeRawVarint32Size(id.get.serializedSize) + id.get.serializedSize }

Any idea how to fix?