通过将属性从一个合并到另一个来加入 MongoDB 中的两个集合

Question

我需要帮助加入 MongoDB 中的两个集合。

我有两个系列：卡片和套牌。我需要加入它们，以便在卡片组文档中拥有卡片文档的属性。下面是每个集合的两个 JSON 格式的示例：

1. 甲板

例子：

{
    "_id": {
        "$oid": "608edd53a8220000b2000882"
    },
    "name": "Izzet Phoenix",
    "cards": {
        "mainboard": [
            {
                "qty": "4",
                "name": "Arclight Phoenix",
                "id": "787de9ce-02c5-4a17-a88b-d38e83dbeb0b"
            },
            ... a bunch of other cards in the same format (qty, name, id)
        ],
        "sideboard": [
            {
                "qty": "2",
                "name": "Abrade",
                "id": "84319dfb-eaf7-4b98-8c4f-30f5e779591b"
            },
            ... a bunch of other cards in the same format (qty, name, id)
        ]
    },
    ... a bunch of other properties of the deck
}

1. 卡片

例子：

{
    "_id": {
        "$oid": "608b60d6a40a0000c9017853"
    },
    "name": "Abrade",
    "id": "84319dfb-eaf7-4b98-8c4f-30f5e779591b",
    ... a bunch of other properties of the card
}

请注意，decks 集合使用卡片的“id”字段作为参考，而不是“_id”字段。

这是我正在寻找的期望输出：

{
    "_id": {
        "$oid": "608edd53a8220000b2000882"
    },
    "name": "Izzet Phoenix",
    "cards": {
        "mainboard": [
            {
                "qty": "4",
                "name": "Arclight Phoenix",
                "id": "787de9ce-02c5-4a17-a88b-d38e83dbeb0b",
                ... add properties of the card Arclight Phoenix, with id = 787de9ce-02c5-4a17-a88b-d38e83dbeb0b
            },
            ... a bunch of other cards
        ],
        "sideboard": [
            {
                "qty": "2",
                "name": "Abrade",
                "id": "84319dfb-eaf7-4b98-8c4f-30f5e779591b",
                ... add properties of the card Abrade, with id 84319dfb-eaf7-4b98-8c4f-30f5e779591b
            },
            ... a bunch of other cards
        ]
    },
    ... a bunch of other properties of the deck
}

我尝试研究如何解决这个问题，我发现 MongoDB 有一个 $lookup 阶段，但我不熟悉管道和阶段的概念，这最终让我望而却步。

感谢所有帮助。

感谢您的宝贵时间！

Answer 1

我能够通过混合使用 $unwind、$lookup、$addFields、$group 和 $project 来解决这个问题。

最终管道：

db.getCollection("decks").aggregate(
    // Pipeline
    [
        // Stage 1
        {
            $match: {
                "_id": ObjectId("608edd53a8220000b2000882")
            }
        },
        // Stage 2
        {
            $unwind: {
                path: "$cards.mainboard"
            }
        },
        // Stage 3
        {
            $lookup: {
                from: "cards",
                localField: "cards.mainboard.id",
                foreignField: "id",
                as: "cards.mainboard.card"
            }
        },
        // Stage 4
        {
            $unwind: {
                path: "$cards.mainboard.card"
            }
        },
        // Stage 5
        {
            $addFields: {
                "cards.mainboard": {
                    "$mergeObjects": ["$cards.mainboard.card", "$cards.mainboard"]
                }
            }
        },
        // Stage 6
        {
            $group: {
                _id: "$_id",
                "name": { "$first": "$name" },
                "cards": { "$first": "$cards" },
                "mainboardCards": { "$push": "$cards.mainboard" },
            }
        },
        // Stage 7
        {
            $project: {
                "mainboardCards.card": 0
            }
        },
        // Stage 8
        {
            $unwind: {
                path: "$cards.sideboard"
            }
        },
        // Stage 9
        {
            $lookup: {
                from: "cards",
                localField: "cards.sideboard.id",
                foreignField: "id",
                as: "cards.sideboard.card"
            }
        },
        // Stage 10
        {
            $unwind: {
                path: "$cards.sideboard.card"
            }
        },
        // Stage 11
        {
            $addFields: {
                "cards.sideboard": {
                    "$mergeObjects": ["$cards.sideboard.card", "$cards.sideboard"]
                }
            }
        },
        // Stage 12
        {
            $group: {
                _id: "$_id",
                "name": { "$first": "$name" },
                "mainboardCards": { "$first": "$mainboardCards" },
                "sideboardCards": { "$push": "$cards.sideboard" },
            }
        },
        // Stage 13
        {
            $project: {
                "sideboardCards.card": 0
            }
        },
    ],
);