pymongo建议的MongoDB推送

Question

I'm trying to learn some basic MongoDB and I'm confused about how to use $push to add more data to my document. Here's the code that i have:

from pymongo import MongoClient
client = MongoClient()
db = client.classes
collection = db.StudentsExample
student1 = {
         'name': 'adam',
         'year': 'sophomore',
         'age': 19,
         'class':[
                  {
                  'className': 'cse131',
                  'time': '2:30',
                  'finalGrade': 'A'
                  },
                  {
                  'className': 'cse240',
                  'time': '9:30',
                  'finalGrade': 'B'
                    }
                  ]
       } 
student2 = {
         'name': 'bob',
         'year': 'sophomore',
         'age': 19,
         'class':[
                  {
                  'className': 'cse131',
                  'time': '2:30',
                  'finalGrade': 'A'
                  },
                  {
                  'className': 'cse240',
                  'time': '9:30',
                  'finalGrade': 'B'
                    }
                  ]
       }

num = int(input("How many more classes?: "))

for x in range(0, num):
    classNameInput = str(input("Class name?: "))
    timeInput = str(input("Time of class?: "))
    finalGradeInput = str(input("Final grade in class?: "))
    db.StudentsExample.update(
        {'name': "adam"},
        {'$push': {'class.className': classNameInput, 'class.time': timeInput, 'class.finalGrade':finalGradeInput}}
        )



cursor = collection.find({})
for document in cursor: print(document)

what i thought this would do is add another document inside the class document in student1. So for example, if the user had input when prompted: Class name: bio time: 2:30 final grade: C

the result would be:

student1 = {
         'name': 'adam',
         'year': 'sophomore',
         'age': 19,
         'class':[
                  {
                  'className': 'cse131',
                  'time': '2:30',
                  'finalGrade': 'A'
                  },
                  {
                  'className': 'cse240',
                  'time': '9:30',
                  'finalGrade': 'B'
                    },
                  {
                   'className': 'bio
                   'time': 2:30
                   'finalGrade': 'C'
                   }
                  ]
       } 
student2 = {
         'name': 'bob',
         'year': 'sophomore',
         'age': 19,
         'class':[
                  {
                  'className': 'cse131',
                  'time': '2:30',
                  'finalGrade': 'A'
                  },
                  {
                  'className': 'cse240',
                  'time': '9:30',
                  'finalGrade': 'B'
                    }

                  ]
       }

I've already inserted both of these elements into the database, so they are in there even though insert method isn't in this code.

However, it's not working-- it gives the error statement "cannot use the part (class of class.time) to traverse the element ({class: [ { finalGrade: "A", time: "2:30", className: "cse131" }, { finalGrade: "B", time: "9:30", className: "cse240" } ]})

Can anyone tell me what I've done wrong? I can't find clear instructions on how to use push with python.. Thanks!

Answer 1

You're almost there:

Change

{'$push': {'class.className': classNameInput, 'class.time': timeInput, 'class.finalGrade':finalGradeInput}

to

{'$push': {class: {'className': classNameInput, 'time': timeInput, 'finalGrade':finalGradeInput}}

The general format is

{'$push': {<array to push to>: <value to push onto array>}}

If we look at your code, you can see you are currently trying to push classNameInput onto array class.className . Mongo then errors out becase class.className is not an array!