How do I conditionally insert an item into a dynamodb table using boto3

Question

If I have a table with a hash key of userId and a range key of productId how do I put an item into that table only if it doesn\'t already exist using boto3\'s dynamodb bindi

Answer 1

i think that you will get better documentation using client.put_item rather than table.put_item

from boto3 documentation:

To prevent a new item from replacing an existing item, use a conditional expression that contains the attribute_not_exists function with the name of the attribute being used as the partition key for the table. Since every record must contain that attribute, the attribute_not_exists function will only succeed if no matching item exists.

ConditionExpression:

ConditionExpression (string) -- A condition that must be satisfied in order for a conditional PutItem operation to succeed.

An expression can contain any of the following:

Functions: attribute_exists | attribute_not_exists | attribute_type | contains | begins_with | size These function names are case-sensitive.

i am using dynamodb2 overwrite parameter on item.save()