Node.js Mongodb：按数组最后一个元素中的值对文档进行排序

我有一个集合“collectionName”，其中包含许多类似以下的文档：

{
    "_id" : ObjectId("5f072d45856bc306147c1dcd"),
    "readOnly" : false,
    "participants" : [ 
        {
            "clientType" : "support",
            "docId" : "",
            "metaData" : {
                "fullName" : "Support",
                "email" : "Support@mydomain.com",
                "phoneNum" : "+1234567890"
            }
        }, 
        {
            "clientType" : "worker",
            "docId" : "5e21c48ee178473be81e032e",
            "metaData" : {
                "fullName" : "Rami",
                "email" : "myemail@gmail.com",
                "phoneNum" : "+1234567890"
            }
        }
    ],
    "messages" : [ 
        {
            "id" : "IGK-fIt-2zz",
            "sender" : "support, ",
            "body" : "CONTROL: Agent \"Greendizeriii\" has answered the conversation",
            "commData" : {
                "sent" : {
                    "state" : true,
                    "dateTime" : ISODate("2020-07-11T06:33:48.348Z")
                },
                "delivered" : {
                    "state" : false
                },
                "seen" : {
                    "state" : true,
                    "dateTime" : ISODate("2020-07-11T06:40:06.851Z")
                }
            }
        }, 
        {
            "id" : "L0f-hwj-QUL",
            "sender" : "support, ",
            "body" : "Hello rami, How can I help you today",
            "commData" : {
                "sent" : {
                    "state" : true,
                    "dateTime" : ISODate("2020-07-11T06:35:57.406Z")
                },
                "delivered" : {
                    "state" : false
                },
                "seen" : {
                    "state" : true,
                    "dateTime" : ISODate("2020-07-11T06:40:06.851Z")
                }
            }
        }, 
        {
            "id" : "n0k-s3u-UmN",
            "sender" : "support, ",
            "body" : "are you still there ?",
            "commData" : {
                "sent" : {
                    "state" : true,
                    "dateTime" : ISODate("2020-07-11T06:36:13.350Z")
                },
                "delivered" : {
                    "state" : false
                },
                "seen" : {
                    "state" : true,
                    "dateTime" : ISODate("2020-07-11T06:40:06.851Z")
                }
            }
        }
    ],
    "controlData" : {
        "isReserved" : {
            "state" : false,
            "reservedUntil" : null,
            "operatorId" : null
        }
    },
    "__v" : 0
},
{
    "_id" : ObjectId("5f1f143f4134643044638902"),
    "readOnly" : false,
    "participants" : [ 
        {
            "clientType" : "support",
            "docId" : "",
            "metaData" : {
                "fullName" : "Support",
                "email" : "Support@mydomain.com",
                "phoneNum" : "+1234567890"
            }
        }, 
        {
            "clientType" : "worker",
            "docId" : "5ea9409ff3243f483c2483ed",
            "metaData" : {
                "fullName" : "Ronaldo",
                "email" : "dummyemail02@gmail.com",
                "phoneNum" : "+1234567890"
            }
        }
    ],
    "messages" : [ 
        {
            "id" : "uto-qQb-0cr",
            "sender" : "support, ",
            "body" : "CONTROL: Agent \"Greendizeriii\" has answered the conversation",
            "commData" : {
                "sent" : {
                    "state" : true,
                    "dateTime" : ISODate("2020-07-27T17:51:59.753Z")
                },
                "delivered" : {
                    "state" : false
                },
                "seen" : {
                    "state" : true,
                    "dateTime" : ISODate("2020-07-27T17:52:01.240Z")
                }
            }
        }, 
        {
            "id" : "FQg-fSQ-jQ1",
            "sender" : "support, ",
            "body" : "jjj",
            "commData" : {
                "sent" : {
                    "state" : true,
                    "dateTime" : ISODate("2020-07-27T17:51:59.751Z")
                },
                "delivered" : {
                    "state" : false
                },
                "seen" : {
                    "state" : true,
                    "dateTime" : ISODate("2020-07-27T17:52:01.240Z")
                }
            }
        }, 
        {
            "id" : "Uqm-J4S-LUT",
            "sender" : "support, ",
            "body" : "CONTROL: Agent \"Greendizeriii\" has left the conversation",
            "commData" : {
                "sent" : {
                    "state" : true,
                    "dateTime" : ISODate("2020-07-27T17:53:05.142Z")
                },
                "delivered" : {
                    "state" : false
                },
                "seen" : {
                    "state" : true,
                    "dateTime" : ISODate("2020-07-27T17:53:05.558Z")
                }
            }
        }, 
        {
            "id" : "gs1-Qqz-jkI",
            "sender" : "worker, 5ea9409ff3243f483c2483ed",
            "body" : "Hello",
            "commData" : {
                "sent" : {
                    "state" : true,
                    "dateTime" : ISODate("2020-07-25T03:58:50.600Z")
                },
                "delivered" : {
                    "state" : false
                },
                "seen" : {
                    "state" : false
                }
            }
        }
    ],
    "controlData" : {
        "isReserved" : {
            "state" : false,
            "reservedUntil" : null,
            "operatorId" : null
        }
    },
    "__v" : 0
}

例如，这里有两个文档

每个字段都有消息字段，该字段是元素/对象的数组

我想使用messages数组的最新元素（

commData.sent.dateTime

）对它们进行排序

我知道我可以做一些事情，比如：

db.getCollection('collectionName').find({}).sort({"messages.0.commData.sent.dateTime": 1})

它将返回使用messages数组中第一个元素的commData.sent.dateTime排序的文档。但我不知道在这种特殊情况下如何使用数组中的最后一个元素进行排序

注意： 问题的答案是： 在我的情况下将不起作用，因为我需要用于对文档进行排序的字段（dateTime）位于嵌套对象内

非常感谢你的帮助

谢谢

您可以用它来计算上次发送日期。将

-1

作为表示数组最后一项的参数：

db.collection.aggregate([
    {
        $addFields: {
            lastSent: {
                $let: {
                    vars: {
                        last: {
                            $arrayElemAt: [ "$messages", -1 ]
                        }
                    },
                    in: "$$last.commData.sent.dateTime"
                }
            }
        }
    },
    { $sort: { lastSent: 1 } },
    { $project: { lastSent: 0 } }
])

---

这是否回答了您的问题？嘿@Gibbs，你建议的答案在我的例子中不起作用，因为我需要用来对文档进行排序的字段（dateTime）位于嵌套对象中。非常感谢@mickl@mickl，如果我想得到与特定过滤器匹配的最后一个对象。我怎么用这个？例如，具有特定“发件人”的最后一封邮件。@letie请打开单独的邮件question@mickl我提出了这个问题：