Mongodb查找列表中包含特定学科名称的所有字典，并提取该字典的个别数据。

Question

这是我的数据集。我花了很多时间在这个问题上，但不能得到我想要的实际结果。请帮我找到我的资料 您可以看到下面的JSON我想提取包含特定学科名称的所有学科，如学科名称：“计算机科学”
然后我只想提取那些包含（学科名称：“计算机科学”）的词典 另外，请告诉我如何获取特定词典的单个数据 我用python做这个 我尝试了以下代码，但得到了实际的输出

import requests
import re
import json
import pymongo
myclient = pymongo.MongoClient("mongodb://localhost:27017/")
mydb = myclient["FYP_DataBase"]
mycol = mydb["balochistan_uni"]
data = mydb.balochistan_uni.find({"disciplines.discipline_name":"Computer Science","disciplines.degree_Name":"BE"},{ '_id':0 ,"disciplines":1,"discipline.discipline_Name" :1, })
for d in data:
    print(d)

。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。你知道吗

{
    "_id" : ObjectId("5b98e604c0c4d54a5016e646"),
    "uni_name" : "Balochistan University Of Engineering & Technology BUET, Khuzdar",
    "location" : "KHUZDAR P.O Box No. 89100 [BALOCHISTAN] ",
    "web_link" : "http://www.buetk.edu.pk ",
    "province" : "Balochistan",
    "category" : "Public",
    "disciplines" : [ 
        {
            "discipline_name" : "Civil",
            "degree_Name" : "BE",
            "duration" : "4 Years",
            "Fee_per_Year" : "NA",
            "admission_date" : "15-09-2018",
            "Last_Merit" : "50"
        }, 
        {
            "discipline_name" : "Computer Science",
            "degree_Name" : "BS",
            "duration" : "4 Years",
            "Fee_per_Year" : "NA",
            "admission_date" : "31-01-2018",
            "Last_Merit" : "NA"
        }, 
        {
            "discipline_name" : "Computer System",
            "degree_Name" : "BE",
            "duration" : "4 Years",
            "Fee_per_Year" : "NA",
            "admission_date" : "15-09-2018",
            "Last_Merit" : "NA"
        }
    ]
}
{
    "_id" : ObjectId("5b98e60dc0c4d54a5016e648"),
    "uni_name" : "Lasbela University Of Agriculture, Water And Marine Sciences, Uthal LUAWMS, Lasbela",
    "location" : "Lasbela ",
    "web_link" : "http://www.luawms.edu.pk ",
    "province" : "Balochistan",
    "category" : "Public",
    "disciplines" : [ 
        {
            "discipline_name" : "Agriculture",
            "degree_Name" : "BS",
            "duration" : "4 Years",
            "Fee_per_Year" : "15000",
            "admission_date" : "14-09-2018",
            "Last_Merit" : "NA"
        }, 
        {
            "discipline_name" : "Business Administration",
            "degree_Name" : "BBA",
            "duration" : "4 Years",
            "Fee_per_Year" : "15000",
            "admission_date" : "14-09-2018",
            "Last_Merit" : "NA"
        }, 
        {
            "discipline_name" : "Computer Science",
            "degree_Name" : "BS",
            "duration" : "4 Years",
            "Fee_per_Year" : "15000",
            "admission_date" : "14-09-2018",
            "Last_Merit" : "NA"
        }
    ]
}

Answer 1

您的查询：

mydb.balochistan_uni.find({
    "disciplines.discipline_name": "Computer Science",
    "disciplines.degree_Name": "BE"
})

检索所有拥有“计算机科学”学科和“BE”学位的大学。您的查询没有指定它应该是具有“be”学位的学科“计算机科学”。你知道吗

如果要这样做，必须匹配数组disciplines中的元素。查询应如下所示：

mydb.balochistan_uni.find({
    "disciplines": {
        "$elemMatch": {
            "discipline_name": "Computer Science",
            "degree_Name": "BE"
        }
    }    
},
{
    "_id": 0, "disciplines": 1
})

现在这个查询将只检索学科名称为“计算机科学”且“计算机科学”的学位名称为“BE”的大学。你知道吗

请查看MongoDB官方的documentation以获取数组查询运算符。
当MongoDB中的字段包含数组时，必须应用这些运算符。你知道吗

Answer 2

要仅筛选符合条件的规程，必须使用聚合框架。一种方法是：

 mydb.balochistan_uni.aggregate(
    [

        {
            $redact: {
                            $cond: {
                                  if: { $or:[
                                    {$eq: [ "$discipline_name", "Computer Science" ] },
                                    { "$ifNull": [ "$disciplines",  false] }
                                    ]},
                                  then: "$$DESCEND",
                                  else: "$$PRUNE"
                                }
            }
        },
        {
            $unwind: {
                path : "$disciplines",

            }
        },
        {
            $replaceRoot: {
                newRoot: "$disciplines"
            }
        },
    ]
);

将返回：

{ 
    "discipline_name" : "Computer Science", 
    "degree_Name" : "BS", 
    "duration" : "4 Years", 
    "Fee_per_Year" : "NA", 
    "admission_date" : "31-01-2018", 
    "Last_Merit" : "NA"
}
{ 
    "discipline_name" : "Computer Science", 
    "degree_Name" : "BS", 
    "duration" : "4 Years", 
    "Fee_per_Year" : "15000", 
    "admission_date" : "14-09-2018", 
    "Last_Merit" : "NA"
}