func (mdb MongoDBConnection) SaveUser(u *structs.User) error {
	mdb.session = mdb.GetSession()
	defer mdb.session.Close()
	if _, err := mdb.LoadUser(u.Email); err == nil {
		return fmt.Errorf("user already exists")
	}
	c := mdb.session.DB("webadventure").C("users")
	err := c.Insert(u)
	return err
}
SaveUser register a user so we know that we saw that user already.
package database
import (
	"fmt"
	"github.com/Skarlso/google-oauth-go-sample/structs"
	"gopkg.in/mgo.v2"
	"gopkg.in/mgo.v2/bson"
)
type MongoDBConnection struct {
	session *mgo.Session
}