How do you marshal a sql.NullString such that the output is flattened to give just the value in go?

Question

Given a go struct

type Company struct {
    ID   int             `json:\"id\"`              
    Abn  sql.NullString  `json:\"abn,string\"`
}

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Answer 1

You cannot, at least not using just sql.NullString and encoding/json.

What you can do is to declare a custom type that embeds sql.NullString and have that custom type implement the json.Marshaler interface.

type MyNullString struct {
    sql.NullString
}

func (s MyNullString) MarshalJSON() ([]byte, error) {
    if s.Valid {
        return json.Marshal(s.String)
    }
    return []byte(`null`), nil
}

type Company struct {
    ID   int          `json:"id"`              
    Abn  MyNullString `json:"abn,string"`
}

https://play.golang.org/p/Ak_D6QgIzLb