mongodb - 从对象数组到数组

Question

我有疑问db.collection('image').find({ category: "concept art"}, { projection: _id: 0, imgUrl:1 }).toArray()并有一个输出:

[
    {
        "imgUrl": "images\\2020-01-23T14-41-48.158Z-abandoned.jpg"
    },
    {
        "imgUrl": "images\\2020-01-25T01-45-14.880Z-pIMG_6443.jpg"
    }
]

我想要这样的输出:

[
"images\\2020-01-23T14-41-48.158Z-abandoned.jpg",
  "images\\2020-01-25T01-45-14.880Z-pIMG_6443.jpg"
]

我在哪里可以找到有关此的信息或如何实现此目标？

Answer 1

您需要尝试 aggregation为了那个原因 :

db.collection.aggregate([
    /** match docs based on criteria same as find */
    { $match: { "category": "concept art" } },
    /** group all docs and push imageUrls to an array */
    { $group: { _id: '', imgUrl: { $push: '$imgUrl' } } },
    /** remove _id from final doc */
    { $project: { _id: 0 } }])

采集数据:

/* 1 */
{
    "_id" : ObjectId("5e2bc27cdc95d08ab83819e8"),
    "category" : "concept art",
    "isImage" : true,
    "imgUrl" : "images\\2020-01-23T14-41-48.158Z-abandoned.jpg"
}

/* 2 */
{
    "_id" : ObjectId("5e2bc27cdc95d08ab83819e9"),
    "category" : "concept art",
    "isImage" : true,
    "imgUrl" : "images\\2020-01-25T01-45-14.880Z-pIMG_6443.jpg"
}

输出:

/* 1 */
{
    "imgUrl" : [ 
        "images\\2020-01-23T14-41-48.158Z-abandoned.jpg", 
        "images\\2020-01-25T01-45-14.880Z-pIMG_6443.jpg"
    ]
}