select function does't work to only get the array i want

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

With a problem like the issue can very well lie in your surrounding code. In the snippet you've given us, `game` is undefined -- are we to assume it's `"dota"` -- and the type `hints` is also undefined. More of your actual code will probably help. Are you certain there isn't more than one document with the name you're looking for? Can you please share the results of `games := make([]Game); err := db.C("games").Find(bson.M{"title": "dota"}).All(games); fmt.Printf("%#v; %s", games, err);` with us? (Snippet untested -- please correct as appropriate.) — icio, Apr 26 '16 at 21:06
I recommend decomposing your query for the sake of debugging. At a glance it looks good to me but most likely one of the earlier operations is not returning what you expect. Unfortunately there is a lot of overhead required to prepare an answer for this so I don't really have the time to help you further. But, if you build your query up one piece at a time checking the results along the way I bet you'll figure it out. — evanmcdonnal, Apr 26 '16 at 22:16

novalagung · Accepted Answer · 2016-04-27T14:10:38.253

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\n", *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\n", *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}}}

tnx, it worked. what should i do to get first 10 hint from the slice ? — CallMeLoki, Apr 27 '16 at 07:58
tnx again but i cant use bson.M{"$slice": [from, limit]} instead of 10, is there a syntax error or what ? — CallMeLoki, Apr 27 '16 at 11:30

select function does't work to only get the array i want

1 Answers1

EDITED 1

EDITED 2