How can I represent a 2-dimensional array in Protocol Buffers?

Question

How can I represent a 2-dimensional array in Protocol Buffers?

I need to store int and double 2d arrays as a field on a PB message, for example:

int[][] multi = new int[5][10];

I'm using C++, Java and C#.

Thanks in advance.

Answer 1

There is no direct support in the protocol for this. Your best bet is to have a repeated set of objects that have an array each - i.e.

message Foo {
    repeated int items = 1;
}
...
repeated Foo foos = 1;

Answer 2

You could try structpb. like this:

.proto

import "google/protobuf/struct.proto";
message Foo {
    repeated google.protobuf.Value array = 1;
}

.go

import (
    "google.golang.org/protobuf/types/known/structpb"
    "google.golang.org/protobuf/encoding/protojson"
)

...
foo := &Foo{}

items := []interface{}{1,2,3,4,5}
l, err := structpb.NewList(items)
foo.array = append(foo.array, structpb.NewListValue(l))

protojson.Format(foo)  // [[1,2,3,4,5]]

Answer 3

It does not work.

I look up the grpc guide, which just supports the key-value structure. I advise you:

message ListResp { 
   repeated Array list = 1;

}

message Array{
     int64 id = 1; // 
    string name = 2; // 
}