从嵌套的对象数组中删除对象mongodb [英] removing object from nested array of objects mongodb

问题描述

我有一个包含志愿者信息的集合，它将志愿者列为一组对象.我可以显示每个志愿者的所有班次，但事实证明，从数组中删除一个班次对我来说很困难:

I've got collection with volunteer information in it, and it lists the volunteers as an array of objects. I can display all the shifts for each volunteer, but removing one from the array is proving difficult for me:

示例数据:

"_id" : ObjectId("59180305c19dbaa4ecd9ee59"),
    "where" : "Merchandise tent",
    "description" : "Sell gear at the merchandise tent.",
    "shifts" : [
            {
                    "dateNeeded" : ISODate("2017-06-23T00:00:00Z"),
                    "timeslot" : "8:00 - NOON",
                    "needed" : 2,
                    "_id" : ObjectId("591807546a71c3a57d1a2105"),
                    "volunteers" : [
                            {
                                    "fullname" : "Mary Mack",
                                    "phone" : "1234567890",
                                    "email" : "[e-mail]",
                                    "_id" : ObjectId("591ce45bc7e8a8c7b742474c")
                            }
                    ]
            },

我可用的数据是:_id, where, shifts.timeslot, shifts.dateNeeded,志愿者.email

The data I have available for this is: _id, where, shifts.timeslot, shifts.dateNeeded, volunteers.email

有人可以帮我吗?假设 Mary Mack 想要在商品帐篷中为 8 点 - 中午的班次志愿服务.她也可能被列入其他班次，但我们只想将她从这个班次中删除.

Can someone help me? Lets say Mary Mack wants to unVolunteer for the 8 - Noon shift at the merchandise tent. She may be listed under other shifts as well, but we only want to remove her from this shift.

推荐答案

您可以通过指定某些内容来匹配文档"，然后指定所需的移位"数组条目作为 .update() 的查询表达式来实现此目的.然后应用 位置 $ 运算符对于与 $pull:

You can do this by specifying something to match the "document" and then the required "shifts" array entry as the query expression for an .update(). Then apply the positional $ operator for the matched array index with $pull:

db.collection.update(
 { "_id": ObjectId("59180305c19dbaa4ecd9ee59"), "shifts.timeslot": "8:00 - NOON" },
 { "$pull": { "shifts.$.volunteers": { "fullname": "Mary Mack" } } }
)

在这种情况下这没问题，因为您只是试图匹配"嵌套结构中的外部"数组和 $pull 有它自己的查询参数来标识要删除的数组条目.

That is okay in this instance since you are only trying to "match" on the "outer" array in the nested structure and the $pull has query arguments of it's own to identify the array entry to remove.

不过，您确实应该小心使用嵌套数组".作为 $pull 操作像这样工作，更新内部"数组是不可能的，因为 位置 $ 运算符 只会匹配满足条件的第一个"元素.因此，您在多个班次中的Mary Mack"示例只会在找到的第一个班次"数组条目中匹配.

You really should be careful using "nested arrays" though. As whilst a $pull operation like this works, updates to the "inner" array are not really possible since the positional $ operator will only match the "first" element that meets the condition. So your example of "Mary Mack" in multiple shifts would only ever match in the first "shifts" array entry found.

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