Is there a way to implement map<string, map<string, list<string>>> in protobuf 3?

Question

I tried this but have scope issues.

message DataCollectionMessage {

    message subData
    {
        message SubDataList {
            repeated string data = 1;
        }
        map<string, subData> parameters = 1;
    }
    map<string,SubDataList> parameters =1;
}

Here SubDataList and subData have unresolved references.

Answer 1

There is just one minor issue with the protobuf in the question: the innermost map uses subData and the outer map uses SubDataList , but it should be the other way round:

message DataCollectionMessage {
    message SubData {
        message SubDataList {
            repeated string data = 1;
        }
        map<string, SubDataList> parameters = 1;
    }
    map<string, SubData> parameters = 1;
}

(I've also capitalized SubData for consistency.)

The generated Java code will have the following classes (snipped and reordered for clarity):

public static final class DataCollectionMessage {

  public Map<String, DataCollectionMessage.SubData> getParametersMap() { ... }

  public static final class SubData {

    public Map<String, DataCollectionMessage.SubData.SubDataList> getParametersMap() { ... }

    public static final class SubDataList {
      public ProtocolStringList getDataList() { ... }
    }
  }
}

Note that SubDataList has a ProtocolStringList , which is like List<String> .

If you get different results, post the protobuf file that you are using and the relevant parts of the generated Java code.