How do I convert a property in MongoDB from text to date type?

This code should do it:

> var cursor = db.ClockTime.find()
> while (cursor.hasNext()) {
... var doc = cursor.next();
... db.ClockTime.update({_id : doc._id}, {$set : {ClockInTime : new Date(doc.ClockInTime)}})
... }

I have exactly the same situation as Jeff Fritz.

In my case I have succeed with the following simpler solution:

db.ClockTime.find().forEach(function(doc) { 
    doc.ClockInTime=new Date(doc.ClockInTime);
    db.ClockTime.save(doc); 
    })

This is a generic sample code in python using pymongo

from pymongo import MongoClient
from datetime import datetime

def fixTime(host, port, database, collection, attr, date_format):
    #host is where the mongodb is hosted eg: "localhost"
    #port is the mongodb port eg: 27017
    #database is the name of database eg : "test"
    #collection is the name of collection eg : "test_collection"
    #attr is the column name which needs to be modified
    #date_format is the format of the string eg : "%Y-%m-%d %H:%M:%S.%f"
    #http://docs.python.org/2/library/datetime.html#strftime-and-strptime-behavior
    client = MongoClient(host, port)
    db = client[database]
    col = db[collection]
    for obj in col.find():
        if obj[attr]:
            if type(obj[attr]) is not datetime:
                time = datetime.strptime(obj[attr],date_format)
                col.update({'_id':obj['_id']},{'$set':{attr : time}})

for more info : http://salilpa.com/home/content/how-convert-property-mongodb-text-date-type-using-pymongo

Starting Mongo 4.x:

• db.collection.update() can accept an aggregation pipeline, finally allowing the update of a field based on its current value (Mongo 4.2+).
• There is a new $toDate aggregation operator (Mongo 4.0).

Such that:

// { a: "2018-03-03" }
db.collection.update(
  {},
  [{ $set: { a: { $toDate: "$a" } } }],
  { multi: true }
)
// { a: ISODate("2018-03-03T00:00:00Z") }

• The first part {} is the match query, filtering which documents to update (in this case all documents).

• The second part [{ $set: { a: { $toDate: "$a" } } }] is the update aggregation pipeline (note the squared brackets signifying the use of an aggregation pipeline). $set is a new aggregation operator which in this case replaces the field's value. The replaced value being the field itself concerted to an ISODate object. Note how a is modified directly based on its own value ($a).

• Don't forget { multi: true }, otherwise only the first matching document will be updated. Or alternatively one can use updateMany instead of update: db.collection.updateMany(...).