Write a list of fields to an associated set of documents in the database

Working with Data
,
1

Hi, as the topic header says, I’m looking for a way to write an aggregation of fields back to a corresponding (equal number and order) set of documents in the database.
For example in the pymongo driver, and I have three documents with a ‘field’ parameter. Is there a single operation to carry out:
collection.update_many(
filter = {“documents”: “documents_key”},
values = {“$set”: {“value” : value1},
{“value” : value2},
{“value” : value3}}).

I don’t want to do it in a loop because it feels inefficient and ‘unclean’ and I’m sure this is a fairly basic question but Google being how it be nowadays I cannot for the life of me find out how to do this. Or if it is even possible

2

What do you mean by

Where is it used in

You have too many parenthesis in your $set. The syntax is

{ "$set" : {
    "field_one" , value_1 ,
    "field_two" , value_2 ,
    "field_three" , value_3
} }

To help you, we will need sample documents that we can cut-n-paste directly into our system. Expected resulting documents based on these sample documents are needed.

3

Hi Steeve,

Let’s say I have a collection in my database that contains however many records.
Now say I construct a filter that specifies 500 of those documents. And I need to set THE SAME FIELD in those 500 documents with a list of 500 values.

I am not setting DIFFERENT fields in the same document, but the same field in different documents.

I know I can use a loop but that doesn’t work with the filter unless I perform a bulk read first to gather the IDs, the ‘for’ loop also feels inefficient as the process jumps from executing business code to executing database code N times.

I only wrote ‘update_many’ as a placeholder for what I meant. Perhaps a poor choice as it overlapped with something that already exists.

4

For n documents, with n different values you need https://www.mongodb.com/docs/manual/reference/method/db.collection.bulkWrite/.

To build the bulkWrite array you will need a loop to build something like:

bulk = [ 
  { "updateOne" : {
      "filter" : { /* filter for first document */ } ,
      "update" : { "field_name" : value_for_first_document }
  } } ,
  { "updateOne" : {
      "filter" : { /* filter for second document */ },
      "update" : { "field_name" : value_for_second_document }
  } } ,
  /* filter and value for other documents */
  { "updateOne" : {
      "filter" : { /* filter for last document */ },
      "update" : { "field_name" : value_for_last_document }
  } } 
]