JSON Decoder cannot decode an object into an object - json

Question

type MiddleMan struct {
User CompletedByUser `json:"user"`
}
type CompletedByUser struct {
DisplayName string `json:"displayName"`
Id string `json:"id"`
}
Using the following types, I run the code
shorterJsonString := `{
"user":{
"displayName":null,
"id":"a03dfee5-a754-4eb9"
}
}`
if !json.Valid([]byte(shorterJsonString)) {
log.Println("Not valid")
}
var middleMan models.MiddleMan
newReader := strings.NewReader(shorterJsonString)
json.NewDecoder(newReader).Decode(&middleMan)
log.Println(middleMan)
Unfortunately, the decoder is seemingly broken for nested objects. Rather than spitting out actual objects, the print prints out
{{ a03dfee5-a754-4eb9 }}
It seems to flatten the whole thing into the id field. What is going on here?

Answer 1

What did you expect to happen / get printed?
The log package (which uses the fmt package) prints structs enclosed in braces, listing field values separated by spaces.
Your MiddleMan has a single field, so it'll look like this:
{field}
Where field is another struct of type CompletedByUser, which has 2 fields, so it'll look like this:
{{field1 field2}}
Where field is of string type, being the empty string, so you'll see the value of field2 prefixed with a space:
{{ a03dfee5-a754-4eb9}}
If you print it adding field names:
log.Printf("%+v", middleMan)
You'll see an output like:
{User:{DisplayName: Id:a03dfee5-a754-4eb9}}
Using another (Go-syntax) format:
log.Printf("%#v", middleMan)
Output:
main.MiddleMan{User:main.CompletedByUser{DisplayName:"", Id:"a03dfee5-a754-4eb9"}}
Try this on the Go Playground.