mongodb`$lookup`或`join`在对象数组中具有属性

我有一个来自mongodb的东西

[
    {
        "_id": "5eaf2fc88fcee1a21ea0d94d",
        "migration_customer_union_id": 517,
        "__v": 0,
        "account": 1,
        "createdAt": "2020-05-03T20:55:36.335Z",
        "customerUnion": "5eaf2fc7698de8321ccd841d",
        "shaufel_customers": [
            {
                "percent": 50,
                "_id": "5eaf2fc8698de8321ccd881f",
                "customer": "5eaf2fb9698de8321ccd68c0"
            },
            {
                "percent": 50,
                "_id": "5eaf2fc9698de8321ccd8a9d",
                "customer": "5eaf2fb9698de8321ccd68c0"
            }
        ],
    }
]

您可以注意到，在shaufel_customers数组中有一个名为customer的属性，我想用它来连接customers文档，所以我就是这么做的（在stackoverflow的帮助下编写了这段代码：）

当执行此代码时，我得到以下响应

[
    {
        "shaufel_customers": [
            {
                "customer_id": "869",
                "percent": 50
            }
        ]
    }
]

您可以注意到我得到了一个对象，尽管上面的原始数组中有两个对象，这是因为上面的customer属性具有相同的ObjectId值

5eaf2fb9698de8321ccd68c0

，这就是我想要问的。即使ID相同，我也希望得到相同的两个对象，因此我在这里期望的结果是

[
    {
        "shaufel_customers": [
            {
                "customer_id": "869",
                "percent": 50
            },
            {
                "customer_id": "869",
                "percent": 50
            },
        ]
    }
]

---

我应该如何做：（

您需要还原

$map

并迭代

shaufel_customers

，而不是

customer

——这将返回两个结果：

{
    $project: {
        shaufel_customer_union_id: 1,
        customerUnion: '$customerUnions',
        shaufel_customers: {
            $map: {
                input: "$shaufel_customers",
                as: "sc",
                in: {
                    $mergeObjects: [
                        "$$c",
                        {
                            $arrayElemAt: [{
                                $filter: {
                                    input: "$customers",
                                    cond: {$eq: ["$$this._id", "$$sc.customer"]}
                                }
                            }, 0]
                        },

                    ]
                }
            },

        }
    }
},

---

成功了！谢谢。你又救了我，谢谢你的帮助。

{
    $project: {
        shaufel_customer_union_id: 1,
        customerUnion: '$customerUnions',
        shaufel_customers: {
            $map: {
                input: "$shaufel_customers",
                as: "sc",
                in: {
                    $mergeObjects: [
                        "$$c",
                        {
                            $arrayElemAt: [{
                                $filter: {
                                    input: "$customers",
                                    cond: {$eq: ["$$this._id", "$$sc.customer"]}
                                }
                            }, 0]
                        },

                    ]
                }
            },

        }
    }
},