CODEWITHSUNDEEP
pythonmongodb
Jack022
Jack022

Reputation: 1257

MongoDB updates entire collection with the same document

I have some documents in my MongoDB collection, they look like this:

number: first
value: 1

number: two
value: 2

number: three
value: 3

I want to update all the documents in the collection so that the value field of each document is changed to a random number, like this:

number: first
value: 4747

number: two
value: 1024

number: three
value: 102

I tried the following code:

cursor = db.mycol.find()

for record in cursor:
    record = db.mycol.raplace_many({}, {"value": random.randrange(10000)})

The problem with this is that instead of updating each document with a new random value, it updates all of them with the same random value, like this:

number: first
value: 1024

number: two
value: 1024

number: three
value: 1024

Why is this happening? I tried the same thing, but with update_many instead of replace, but the output is the same. Every advice is appreciated!

On the other hand, if i try to insert the value using insert_one the output will be the expected, so each field will have a different random value.

Upvotes: 0

Views: 74

Answers (1)

Himanshu Sharma
Himanshu Sharma

Reputation: 3010

The following code can do the trick:

//Fetching the array of object IDs from the collection.
var objectIDs= db.collection.distinct("_id");

// Iterating over the array and updating the 'value' correspond to each object ID with a random value. Since there is a default index on object ID, the operation would be fast.
objectIDs.forEach(id=>{
    db.collection.update(
        {
            "_id":id
        },
        {
            $set:{
                "value": Math.floor(Math.random() * 10000)
            }
        }
    )   
});

Before update:

{ "_id" : ObjectId("5d8774e19f062d4c422b3ab4"), "value" : 1 }
{ "_id" : ObjectId("5d8774e19f062d4c422b3ab5"), "value" : 1 }
{ "_id" : ObjectId("5d8774e19f062d4c422b3ab6"), "value" : 1 }
{ "_id" : ObjectId("5d8774e19f062d4c422b3ab7"), "value" : 1 }
{ "_id" : ObjectId("5d8774e19f062d4c422b3ab8"), "value" : 1 }
{ "_id" : ObjectId("5d8774e19f062d4c422b3ab9"), "value" : 1 }
{ "_id" : ObjectId("5d8774e19f062d4c422b3aba"), "value" : 1 }
{ "_id" : ObjectId("5d8774e19f062d4c422b3abb"), "value" : 1 }
{ "_id" : ObjectId("5d8774e19f062d4c422b3abc"), "value" : 1 }
{ "_id" : ObjectId("5d8774e19f062d4c422b3abd"), "value" : 1 }

After update:

{ "_id" : ObjectId("5d8774e19f062d4c422b3ab4"), "value" : 3538 }
{ "_id" : ObjectId("5d8774e19f062d4c422b3ab5"), "value" : 9678 }
{ "_id" : ObjectId("5d8774e19f062d4c422b3ab6"), "value" : 8325 }
{ "_id" : ObjectId("5d8774e19f062d4c422b3ab7"), "value" : 2986 }
{ "_id" : ObjectId("5d8774e19f062d4c422b3ab8"), "value" : 6159 }
{ "_id" : ObjectId("5d8774e19f062d4c422b3ab9"), "value" : 4564 }
{ "_id" : ObjectId("5d8774e19f062d4c422b3aba"), "value" : 7185 }
{ "_id" : ObjectId("5d8774e19f062d4c422b3abb"), "value" : 2585 }
{ "_id" : ObjectId("5d8774e19f062d4c422b3abc"), "value" : 7073 }
{ "_id" : ObjectId("5d8774e19f062d4c422b3abd"), "value" : 4094 }

Upvotes: 1

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