使用Boto3，如果对象上存在某些属性，请获取put_item替换DynamoDB中的对象？

Question

I'm having issues getting Boto3's put_item to replace an object in DynamoDB if certain attributes (some of which are the primary keys of the DynamoDB table, and some of which are not) match up with the new object that I'm inserting into the table.

For instance, if a DynamoDB table has within it:

user (Partition Key) | ts (Sort Key) | height | weight
__________________________________________________________________________________

'fred'                  01-01-2017     5'10''   190
'george'                01-02-2017     5'08''   200

and I'm trying to add a new row to this table:

'fred'                 01-01-2018     5'10''    200

Based on the user fred and the height 5'10'' matching another user already in the table, I'd like to substitute the new entry for the old one. The docs are bit unclear for boto3 and AWS put_item -- how do I do so?

For reference, this is what I have currently:

 tracking_result = tracking_dbs[drivetype].put_item(
      Item=track,
      # insert fields to remove old entry that matches
      # up with certain attributes from new entry here
  )

Answer 1

The already existing entry in the DynamoDB will be replaced by the new entry only if the partition key and the sort key of the new entry matches that of the existing entry. Otherwise a new entry will be created.

In your case you have to delete the existing entry( by getting the existing entry by scanning and not querying as querying requires both partition and sort key as input parameters and then performing the delete operation) and then creating the new entry.