选择功能不起作用只获得我想要的数组

Question

i have a document like this

{
"_id": {
    "$oid": "570bc73da8ebd9005dd54de3"
},
"title": "dota",
"imgurl": "asd.com",
"description": "",
"hints": [
    {
        "date": "2016-04-26 22:50:12.6069011 +0430 IRDT",
        "description": "narinin"
    },
    {
        "date": "2016-04-26 22:50:12.6069011 +0430 IRDT",
        "description": "doros shod"
    }
]
}

the script i execute is

hints := hints{}
err := db.C("games").Find(bson.M{"title": game}).Select(bson.M{"hints": 0}).One(&hints)

my 2 structs are

type Game struct {
Id          bson.ObjectId `bson:"_id,omitempty"`
Title       string        `json:"title"`
Imgurl      string        `json:"imgurl"`
Description string        `json:"desc"`
Hints       []*hint       `bson:"hints", json:"hints"`
}

type hint struct {
    Description string    `json:"desc"`
    Date        time.Time `json:"date"`
}

when i use the script all i get is a none sense date string witch is not even in document how can i get just the slice of hints from a game

Answer 1

You have too keep using Game struct to receive the result, even for only hints column. Also your select query should be .Select(bson.M{"hints": 1}).

I fixed your code, and tried in my local, this one is working.

game := Game{}
err = db.C("games").Find(bson.M{"title": "dota"})
        .Select(bson.M{"hints": 1}).One(&game)
if err != nil {
    panic(err)
}

for _, hint := range game.Hints {
    fmt.Printf("%#v
", *hint)
}

All properties of game is empty, except Hints.

EDITED 1

To get the first 10 rows on hints, the easiest way would be by playing the slice, but this is bad because it need to fetch all the rows first.

for _, hint := range game.Hints[:10] { // 10 rows
    fmt.Printf("%#v
", *hint)
}

The other solution (which is better), is by using $slice on the .Select() query.

selector := bson.M{"hints": bson.M{"$slice": 10}} // 10 rows

err = db.C("so").Find(bson.M{"title": "dota"})
        .Select(selector).One(&game)

EDITED 2

Use []int{skip, limit} on the $slice, to support skip and limit.

selector := bson.M{"hints": bson.M{"$slice": []int{0, 10}}}