MongoDB：如何为单个文档投影所有字段类型？

我需要检查给定集合中每个文档中的每个字段类型

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虽然我可以为每个字段编写单独的

$type

命令，并分别为每个文档进行匹配，但我想知道是否有一种更优雅、更高效的方法可以直接投影所有字段类型。

您需要枚举所有字段并单独处理每个字段。为了枚举的目的，您可以结合使用

$objectToArray

和

$unwind

，然后使用

$push

和

$arrayToObject

将所有内容重新分组在一起：

db.collection.aggregate([
    // Convert the root document into an array.
    {$project: {
        fields: {
            $objectToArray: "$$ROOT"
        }
    }},

    // Turn each array element into a separate document representing a field-value pair of the root document.
    {$unwind: "$fields"},

    // Apply the $type projection to the value portion of the field-value pair.
    {$project: {
        fields: {
            k: "$fields.k",
            v: {$type: "$fields.v"}
        }
    }},

    // Grab the first instance of each unique field name.
    {$group: {
        _id: "$fields.k",
        fields: {$first: "$fields"}
    }},

    // Take the unique field instances and recollect them all into an array.
    {$group: {
        _id: null,
        fields: {$push: "$fields"}
    }},

    // Convert our array back into an object.
    {$project: {
        fields: {$arrayToObject: "$fields"}
    }},

    // Replace the root document with our nested "fields" sub-document.
    {$replaceRoot: {
        newRoot: "$fields"
    }}
])

一个小警告：如果字段可能包含多种类型，例如“string”和“null”，则此解决方案不会考虑这种情况。要解决此问题，您需要修改

$group

阶段，以使用

$addToSet

操作符收集每个键的唯一

$type

实例，然后再

$push

将其放入

字段数组中。
尝试以下操作：

db.collection.aggregate([{
    $addFields: {
        types: {
            $arrayToObject: {
            $map:
            {
                input: { $objectToArray: "$$ROOT" },
                as: "each",
                in: { k: '$$each.k', v: { $type: '$$each.v' } }
            }
        }}
    }
}])

收集数据：

/* 1 */
{
    "_id" : ObjectId("5e065992400289966eefb9a8"),
    "username" : "myName",
    "blog" : "myBlog",
    "details" : "myBlogDetails",
    "Object" : {
        "inOneObject" : true
    }
}

/* 2 */
{
    "_id" : ObjectId("5e0659ae400289966eefbc3a"),
    "username" : "othersName",
    "blog" : "not a blog",
    "details" : "useless"
}

/* 1 */
{
    "_id" : ObjectId("5e065992400289966eefb9a8"),
    "username" : "myName",
    "blog" : "myBlog",
    "details" : "myBlogDetails",
    "Object" : {
        "inObject" : true
    },
    "types" : {
        "_id" : "objectId",
        "username" : "string",
        "blog" : "string",
        "details" : "string",
        "Object" : "object"
    }
}

/* 2 */
{
    "_id" : ObjectId("5e0659ae400289966eefbc3a"),
    "username" : "othersName",
    "blog" : "not a blog",
    "details" : "useless",
    "types" : {
        "_id" : "objectId",
        "username" : "string",
        "blog" : "string",
        "details" : "string"
    }
}

结果：

/* 1 */
{
    "_id" : ObjectId("5e065992400289966eefb9a8"),
    "username" : "myName",
    "blog" : "myBlog",
    "details" : "myBlogDetails",
    "Object" : {
        "inOneObject" : true
    }
}

/* 2 */
{
    "_id" : ObjectId("5e0659ae400289966eefbc3a"),
    "username" : "othersName",
    "blog" : "not a blog",
    "details" : "useless"
}

/* 1 */
{
    "_id" : ObjectId("5e065992400289966eefb9a8"),
    "username" : "myName",
    "blog" : "myBlog",
    "details" : "myBlogDetails",
    "Object" : {
        "inObject" : true
    },
    "types" : {
        "_id" : "objectId",
        "username" : "string",
        "blog" : "string",
        "details" : "string",
        "Object" : "object"
    }
}

/* 2 */
{
    "_id" : ObjectId("5e0659ae400289966eefbc3a"),
    "username" : "othersName",
    "blog" : "not a blog",
    "details" : "useless",
    "types" : {
        "_id" : "objectId",
        "username" : "string",
        "blog" : "string",
        "details" : "string"
    }
}

注意：此给定查询仅适用于文档中的顶级字段，它不会从以下字段中获取对象的类型：

：

"Object" : {
            "inOneObject" : true
        }

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您是否尝试过使用mongo Compass产品

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我相信对于这个要求来说这很容易……

这可能正适合我的需要。谢谢你们两位。@Ben:嘿，你们能接受这个吗？这样你们的问题就会被标记为完整的，并有一个有效的答案。。