Unmarshaling nested JSON objects in Golang

Question

There are a few questions on the topic but none of them seem to cover my case, thus I'm creating a new one.

I have JSON like the following:

{"foo":{ "bar": "1", "baz": "2" }, "more": "text"}

Is there a way to unmarshal the nested bar property and assign it directly to a struct property without creating a nested struct?

The solution I'm adopting right now is the following:

type Foo struct {
    More String `json:"more"`
    Foo  struct {
        Bar string `json:"bar"`
        Baz string `json:"baz"`
    } `json:"foo"`
    //  FooBar  string `json:"foo.bar"`
}

This is a simplified version, please ignore the verbosity. As you can see, I'd like to be able to parse and assign the value to

//  FooBar  string `json:"foo.bar"`

I've seen people using a map, but that's not my case. I basically don't care about the content of foo (which is a large object), except for a few specific elements.

What is the correct approach in this case? I'm not looking for weird hacks, thus if this is the way to go, I'm fine with that.

Answer 1

Is there a way to unmarshal the nested bar property and assign it directly to a struct property without creating a nested struct?

No, encoding/json cannot do the trick with ">some>deep>childnode" like encoding/xml can do. Nested structs is the way to go.

Answer 2

I was working on something like this. But is working only with structures generated from proto. https://github.com/flowup-labs/grpc-utils

in your proto

message Msg {
  Firstname string = 1 [(gogoproto.jsontag) = "name.firstname"];
  PseudoFirstname string = 2 [(gogoproto.jsontag) = "lastname"];
  EmbedMsg = 3  [(gogoproto.nullable) = false, (gogoproto.embed) = true];
  Lastname string = 4 [(gogoproto.jsontag) = "name.lastname"];
  Inside string  = 5 [(gogoproto.jsontag) = "name.inside.a.b.c"];
}

message EmbedMsg{
   Opt1 string = 1 [(gogoproto.jsontag) = "opt1"];
}

Then your output will be

{
"lastname": "Three",
"name": {
    "firstname": "One",
    "inside": {
        "a": {
            "b": {
                "c": "goo"
            }
        }
    },
    "lastname": "Two"
},
"opt1": "var"
}