Question

我有一个像这样的集合

 {
    "_id" : ObjectId("53a7fb486201281a1f698fe4"),
    "userId" : ObjectId("53a7fade6201281a1f698fd9"),
    "magic" : [
    {
        "power" : 0,
        "mana" : 10,
        "foo" : null,
        "bar" : 150
    },
    {
        "power" : 2,
        "mana" : 2,
        "foo" : 200,
        "bar" : 1
    },
]
}

{
    "_id" : ObjectId("53a7fb486201281a1f698fe4"),
    "userId" : ObjectId("53a7fade6201281a1f698fd9"),
    "magic" : [
    {
        "power" : 20,
        "mana" : 210,
        "foo" : null,
        "bar" : 2150
    },
    {
        "power" : 23,
        "mana" : 23,
        "foo" : 2004,
        "bar" : 14
    },
]
}

{
    "_id" : ObjectId("53a7fb486201281a1f698fe4"),
    "userId" : ObjectId("anotherID"),
    "magic" : [
    {
        "power" : 20,
        "mana" : 210,
        "foo" : null,
        "bar" : 2150
    },
    {
        "power" : 23,
        "mana" : 23,
        "foo" : 2004,
        "bar" : 14
    },
]
}

我想创建一个独特的数组“magic of userId ObjectId("53a7fade6201281a1f698fd9")

我确实试过这个

db.myColl.aggregate([
{       

    '$group': {
            _id: {
                magic: "$magic",
            },
            "allmagic": {
                $push: "$magic"
            },
        },
}
]);

结果是我的集合中所有魔法数组的数组myColl 然后我尝试使用$match

db.myColl.aggregate([
{       

    '$group': {
            _id: {
                magic: "$magic",
            },

            "allmagic": {
                $push: "$magic"
            },
        },
        $match : { "userId" : ObjectId("53a7fade6201281a1f698fd9") }
}
]);

但我有这个错误 exception: A pipeline stage specification object must contain exactly one field.。然后我想在node.js中使用它（我也使用mongoose）

Answer 1

在聚合框架中使用数组，尤其是要使用$unwind运算符的文档：

db.myColl.aggregate([

    // Match documents for user id first
    { "$match": { "userId": ObjectId("53a7fade6201281a1f698fd9") }},

    // Unwind the array
    { "$unwind": "$magic" },

    // Group back to a single user document
    { "$group": {
        "_id": "$userId",
        "magic": { "$addToSet": "$magic" }
    }}
])

$addToSet运算符保留数组的元素＆＃34;唯一＆＃34;，如果您只想在不删除重复项的情况下进行组合，则使用$push代替。

从两个或多个文档创建唯一的数组

1 个答案: