mongodb - 如何计算 MongoDB 中嵌入文档中的字段数

Question

我有一个文件如下:

{
    "_id" : ObjectId("58f5f4e0e405972824b8ff03"),
    "type" : "Defect Status",
    "data" : {
        "1" : [ "121764", "Bug", "7/6/15", "Closed" ],
        "2" : [ "121830", "Bug", "7/7/15", "Closed" ],
        "3" : [ "122333", "Bug", "7/16/15","Closed"],
        "4" : [ "122339", "Bug", "7/16/15","Closed"],
        "5" : [ "122340", "Bug", "7/16/15", "Closed"]
     }
}

我想计算 data 字段中的字段数，该字段是另一个文档中的嵌入文档。因为它不是数组，所以我找不到办法。

Answer 1

您可以使用版本 3.4.4 中引入的新 $objectToArray 表达式:https://jira.mongodb.org/browse/SERVER-18794

db.test.aggregate([{$project: {data_size: {$size: {$objectToArray: "$data"}}}}])