Go map[int]struct JSON Marshal

Question

Trying to parse a map[int] to user defined struct in go:

Here are the data schemas.

type Recommendation struct {
    Book  int     `json:"book"`
    Score float64 `json:"score"`
}

Here is the json marshaling:

ureco := make(map[int]data.Recommendation)
ureco, _ = reco.UserRunner()

json, _ := json.Marshal(ureco)
fmt.Println(json)

Where reco.UserRunner() returns the appropriate struct type.

This prints an empty json object:

[]

UPDATE:

error message:

json: unsupported type: map[int]data.Recommendation

So how do I json a map of structs? or is there an alternative approach?

Answer 1

If you just need to marshal it, you could just iterate over your map and turn it into a slice.

slc := make([]data.Recommendation)
for _, val := range ureco {     
    slc = append(out, val)
}
json, _ := json.Marshal(slc)

You can see a simple example with a map[int]string here: http://play.golang.org/