Question 18711 in Amazon Web Sevices Question posted in
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Dynamodb – GetItem operation: The provided key element does not match the schema – Amazon Web Sevices

I’m using python to query a dynamodb table,however I’m using two keys in the getitem call that are not part of the primary key or sort key.I created a global index that contains these two keys, but I still get the same error.

  response = table.get_item(
            Key={
                'player_id': 22892251,'type': 1
            }
        )
  item = response['Item']
  print(item)

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2

Answers


  1. 0

    You cannot issue a GetItem against a secondary index as items are not unique.

    You must use a Query request.

    response = table.query(
IndexName='player_id-type-index'
KeyConditionExpression=Key('player_id').eq(22892251) & Key('type').eq(1) )
items = response['Items']
print(items)
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  2. 0

    You’re trying to use GetItem to fetch data from a global secondary index. This is not supported. The GetItem API returns exactly 1 item, which is only possible because the Primary Key (Partition + Sort Key) is guaranteed to be unique in the base table.

    This is not the case for global secondary indexes, which is why GetItem is not supported here. It requires a guarantee that the underlying data structure does not give.

    The way to fetch this data is to use the Query operation that can return multiple items:

    import boto3

from boto3.dynamodb.conditions import Key

table = boto3.resource("dynamodb").Table("table_name")

response = table.query(
    KeyConditionExpression=Key("player_id").eq(number) & Key("type").eq(number),
    IndexName="player_id-type-index"
)

items = response["Items"]

if len(items) > 1:
    raise RuntimeError("Something broke our unique expectation")

print(items[0])

    It’s on your app to ensure that the entries are unique if you require it. Here’s an example that lets you detect if this assumption got broken somehow.

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