我有一个包含嵌套球员的团队数据库,如下所示:
{
team_id: "eng1",
date_founded: new Date("Oct 04, 1896"),
league: "Premier League",
points: 62,
name: "Manchester United",
players: [ { p_id: "Rooney", goal: 85, caps: 125, age: 28 },
{ p_id: "Scholes", goal: 15, caps: 225, age: 28 },
{ p_id: "Giggs", goal: 45, caps: 359, age: 38 } ]
}
我正在尝试计算每个团队的平均年龄(所有球员年龄的平均值),但是我无法正确访问$player.age的值。
cursor = db.teams.aggregate({
$group : { _id: "$name", avgAge : {
$avg : "$players.age" }
}
});
这只会返回以下内容:
{
{ "_id": "AC Milan", avgAge: 0 },
{ "_id": "Barcelona", avgAge: 0 }
{ "_id": "Real Madrid", avgAge: 0 }
...
}
(所有玩家的年龄都有)需要帮忙吗?
"$players.age"
仍然会得到相同的结果。 - Rich131