How to insert math/big.Int in mongo via mgo in golang - mongodb

Question

I have a struct that contains math/big.Int fields. I would like to save the struct in mongodb using mgo. Saving the numbers as a strings is good enough in my situation.
I have looked at the available field's tags and nothing seams to allow custom serializer. I was expecting to implement an interface similar to encoding/json.Marshaler but I have found None of such interface in the documentation.
Here is a trivial example of what I want I need.
package main
import (
"labix.org/v2/mgo"
"math/big"
)
type Point struct {
X, Y *big.Int
}
func main() {
session, err := mgo.Dial("localhost")
if err != nil {
panic(err)
}
defer session.Close()
c := session.DB("test").C("test")
err = c.Insert(&Point{big.NewInt(1), big.NewInt(1)})
if err != nil { // should not panic
panic(err)
}
// The code run as expected but the fields X and Y are empty in mongo
}
Thnaks!

Answer 1

The similar interface is named bson.Getter:
http://labix.org/v2/mgo/bson#Getter
It can look similar to this:
func (point *Point) GetBSON() (interface{}, error) {
return bson.D{{"x", point.X.String()}, {"y", point.Y.String()}}, nil
}
And there's also the counterpart interface in the setter side, if you're interested:
http://labix.org/v2/mgo/bson#Setter
For using it, note that the bson.Raw type provided as a parameter has an Unmarshal method, so you could have a type similar to:
type dbPoint struct {
X string
Y string
}
and unmarshal it conveniently:
var dbp dbPoint
err := raw.Unmarshal(&dbp)
and then use the dbp.X and dbp.Y strings to put the big ints back into the real (point *Point) being unmarshalled.