Query Document with different struct for results - go

Question

I have a collection of documents that were inserted into Mongo looking something like this:
type Stats struct {
UserStatus string `json:"userStatus" bson:"userStatus"`
... a bunch more fields
}
type User struct {
ID bson.ObjectId `json:"-" bson:"_id"`
LastName string `json:"lastName" bson:"lastName"`
FirstName string `json:"firstName" bson:"firstName"`
Role string `json:"role" bson:"role"`
Tags []string `json:"tags" bson:"tags"`
... (a bunch more fields)
Stats UserStats `json:"stats" bson:"stats"`
}
I want to query it to get a specific report, so I tried this:
func UserNameReport() {
... get mongo session, etc.
// create struct of just the data I want returned
type UserNames struct {
LastName string `json:"lastName" bson:"lastName"`
FirstName string `json:"firstName" bson:"firstName"`
... etc
UserStats Stats `json:"stats" bson:"stats"`
}
projection := bson.M{"lastName":1, "firstName":1, etc}
result := []UserNames{}
err := x.Find({query user collection}).Select(projection).All(&result)
...
}
This works - my question is, how can I include just ONE field from the 'Stats' struct? In other words,
I essentially want the "projection" to be this:
projection := bson.M{"lastName":1, ..., "stats.userStatus":1} <-- stats.userStatus doesn't work
...
err := x.Find({query user collection}).Select(projection).All(&result)
I get the entire "Stats" embedded struct in the results - how can I filter out just one field from the sub-document in and put it into the result set?
Thanks!

Answer 1

It works perfectly for me, with MongoDB 2.6.5
The following code:
package main
import (
"fmt"
"gopkg.in/mgo.v2"
"gopkg.in/mgo.v2/bson"
"log"
)
type Statistics struct {
Url string
Hits int
}
type Person struct {
Num int
Uuid string
Name string
Stats []Statistics
}
func main() {
// Connect to the database
session, err := mgo.Dial("localhost")
if err != nil {
panic(err)
}
defer session.Close()
// Remove people collection if any
c := session.DB("test").C("people")
c.DropCollection()
// Add some data
err = c.Insert(
&Person{1, "UUID1", "Joe", []Statistics{Statistics{"a", 1}, Statistics{"b", 2}}},
&Person{2, "UUID2", "Jane", []Statistics{Statistics{"c", 3}, Statistics{"d", 4}}},
&Person{3, "UUID3", "Didier", []Statistics{Statistics{"e", 5}, Statistics{"f", 6}}})
if err != nil {
log.Fatal(err)
}
result := []Person{}
err = c.Find(bson.M{"$or": []bson.M{bson.M{"uuid": "UUID3"}, bson.M{"name": "Joe"}}}).Select(bson.M{"num": 1, "name": 1, "stats.hits": 1}).All(&result)
if err != nil {
log.Fatal(err)
}
fmt.Println(result)
}
results in:
[{1 Joe [{ 1} { 2}]} {3 Didier [{ 5} { 6}]}]
... which is precisely what I would expect.

Answer 2

Maybe this will help others - essentially I was trying to take a document with an embedded document and return a result set like I would do in SQL with a select a.LastName + ', ' + a.FirstName as Name, b.OtherData and in essence have a different 'table' / 'document'.
So here is my current solution - love to get better ones (more performant?) though!
I created a new struct and I'm using the 'mapstructure' library
import "github.com/goinggo/mapstructure"
type Stats struct {
UserStatus string `json:"userStatus" bson:"userStatus"`
... a bunch more fields
}
type User struct {
ID bson.ObjectId `json:"-" bson:"_id"`
LastName string `json:"lastName" bson:"lastName"`
FirstName string `json:"firstName" bson:"firstName"`
Role string `json:"role" bson:"role"`
Tags []string `json:"tags" bson:"tags"`
... (a bunch more fields)
Stats UserStats `json:"stats" bson:"stats"`
}
type MyReportItem struct {
FirstName string `json:"firstName" jpath:"firstName"`
LastName string `json:"lastName" jpath:"lastName"`
Status string `json:"status" jpath:"stats.userStatus"`
}
type MyReport struct {
Results []MyReportItem `json:"results"`
}
func xxxx(w http.ResponseWriter, r *http.Request) {
var users MyReportItem
// the results will come back as a slice of map[string]interface{}
mgoResult := []map[string]interface{}{}
// execute the query
err := c.Find(finder).Select(projection).All(&mgoResult)
if err != nil {
http.Error(w, err.Error(), http.StatusInternalServerError)
return
}
user := MyReportItem{}
// iterate through the results and decode them into the MyReport struct
for _, x := range mgoResult {
docScript, _ := json.Marshal(x)
docMap := map[string]interface{}{}
json.Unmarshal(docScript, &docMap)
err := mapstructure.DecodePath(docMap, &user)
if err == nil {
users.Results = append(users.Results, user)
}
}
... send back the results ...
_ := json.NewEncoder(w).Encode(&users)
}
Now I get a slice of objects in the form:
results: [
{
firstName: "John",
lastName: "Doe",
status: "active"
}
...
]
Instead of:
{
firstName: "John",
lastName: "Doe",
stats: {
status: "active"
}
}