How to deal with Structs?

[mirkolenz]

I just discovered this library and am very pleased overall! I am struggling a bit with properly handling protobuf structs. In the default Python bindings, I am able to use any dict containing JSON-serializable values directly to my struct. I am not able to achieve this with this library however. Let me give a short example. Consider the following protobuf definition:

import "google/protobuf/struct.proto";

message Request {
  google.protobuf.Struct metadata = 1;
}

In Typescript, I now try to create such a message with the following code

import { Request } from "...";

const req: Request = {
  metadata = { id: 1 }
}

I get the following error:

Type '{ id: number; }' is not assignable to type 'Struct'.
  Object literal may only specify known properties, and 'id' does not exist in type 'Struct'.

The problem seems to be that such structs are also strongly typed according to the actual serialization format. Thus, a struct is defined as follows:

fields: {
  [key: string]: Value;
};

I also tried to assign my metadata as follows:

import { Request } from "...";

const req: Request = {
  metadata = { fields: { id: 1 } }
}

In this case, I get the error

Type 'number' is not assignable to type 'Value'.

Value is defined as follows:

export interface Value {
    /**
     * @generated from protobuf oneof: kind
     */
    kind: {
        oneofKind: "nullValue";
        /**
         * Represents a null value.
         *
         * @generated from protobuf field: google.protobuf.NullValue null_value = 1;
         */
        nullValue: NullValue;
    } | {
        oneofKind: "numberValue";
        /**
         * Represents a double value.
         *
         * @generated from protobuf field: double number_value = 2;
         */
        numberValue: number;
    } | {
        oneofKind: "stringValue";
        /**
         * Represents a string value.
         *
         * @generated from protobuf field: string string_value = 3;
         */
        stringValue: string;
    } | {
        oneofKind: "boolValue";
        /**
         * Represents a boolean value.
         *
         * @generated from protobuf field: bool bool_value = 4;
         */
        boolValue: boolean;
    } | {
        oneofKind: "structValue";
        /**
         * Represents a structured value.
         *
         * @generated from protobuf field: google.protobuf.Struct struct_value = 5;
         */
        structValue: Struct;
    } | {
        oneofKind: "listValue";
        /**
         * Represents a repeated `Value`.
         *
         * @generated from protobuf field: google.protobuf.ListValue list_value = 6;
         */
        listValue: ListValue;
    } | {
        oneofKind: undefined;
    };
}

Here I stopped my investigation, because as you can see, it is essentially a 1-to-1 mapping of the underlying format of a protobuf struct.

Thus my question is: Are structs currently not supported (they are at least not listed in the well-known types in the manual) or did I just not find the correct way of using them?

[timostamm]

Hi Mirko, you are correct, we're representing Struct exactly like it's defined in it's proto source.

I agree it is terrible to use 😆

However, Struct maps perfectly to a JSON object (and our JsonObject type), so you can do:

Struct.fromJson({
  "foo": "you can put any JSON here",
  "bar": 123,
});

Does that help?

[mirkolenz]

Thank you so much for the suggestion, that works beautifully. Maybe you could add this to your excellent manual the next time you make modifications to it?