How do I lowercase a nested struct name when using json.marshal?

November 9, 2021

I’m exposing a REST endpoint with some data. It’s a struct, say:

type status struct {
    Config struct {
        Allow   bool `json:"allow"`
        Expired bool `json:"expired"`
    }
    Database struct {
        Healthy          bool   `json:"healthy"`
        WaitCount        int64  `json:"wait_count"`
    }
}

I’m using the json tag to denote how a struct field should look when calling the endpoint. Using the above, I’m getting the following payload as response:

{
    "Config": {
        "allow": false,
        "expired": false,
    },
    "Database": {
        "healthy": true,
        "wait_count": 1,
    },
}

I’d like for Config and Database to be lowercase, meaning config and database. However, changing them to that in the Go code means the "encoding/json" package cannot "see" them as they aren’t exported outside of the package scope.

How do I lowercase the nested struct’s in the json response payload?

>Solution :

The nested struct is a field in the containing struct. Add a field tags as you did with the other fields:

type status struct {
    Config struct {
        Allow   bool `json:"allow"`
        Expired bool `json:"expired"`
    } `json:"config"` // <-- add tag here ...
    Database struct {
        Healthy          bool   `json:"healthy"`
        WaitCount        int64  `json:"wait_count"`
    } `json:"database"` // <-- ... and here
}