I am working on MongoDB. I am trying to append some new key-value pairs to my existing collection. I got more than 50 documents in my collection, in all of which I want to update a new key value pair. In the new key value pair I am adding, one of the values of the key should be from one of the existing key value pair of the same collection. For example:
{ name : "algebra", quantity : 25 }
Now I want to update each of the document with
{ category : "maths" , available_quantity : 25 }
Without entering distinctly for every document its available quantity. I want it to be picked from it's respective quantity's value, and be inserted in the new key available_quantity. I am using the code to update the document :
db.books.update( {} , { $set : { category : "maths" , available_quantity : `__ ? __` }, false, true }
What best can I put in __ ? __ block?
You can do it with Aggregation framework:
db.books.update({},
[
{
"$set": {
"available_quantity": "$quantity"
}
}
],
{
multi: true
})