boto3: where is attribute_not_exists function documented?

Question

I'd like my lambda to add a new item to a dynamo db table using 'put_item'. I'd like to check before adding the item that an item in the table with the same primary key as the identifier for the new item I've generated does not exist before adding the item. Here's what the boto3 docs say about how to do that:

Enter image description here

That's nice, but it doesn't give me a link to any documentation about "the attributes_not_exists function", whatever that is.

Where is that function documented?

![Enter image description here](/media/postImages/original/IMzQxGiOIMSr6zAs6oNAcQcA)

That's nice, but it doesn't give me a link to any documentation about "the `attributes_not_exists` function", whatever that is.

Where is that function documented?

Leo K · Accepted Answer

The DynamoDB function `attribute_not_exists` is documented here: https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Expressions.OperatorsAndFunctions.html#Expressions.OperatorsAndFunctions.Functions

And just the kind of conditional put you are intending to implement is explained in more detail here: https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Expressions.ConditionExpressions.html#Expressions.ConditionExpressions.PreventingOverwrites

iBehr · Answer

Do a Ctrl-F and search for the term further down the same doc.

To use it fit it in the overall call in the ConditionExpression

response = client.put_item(
    TableName='string',
    Item={
        'string': {
            'S': 'string',
            'N': 'string',
            'B': b'bytes',
            'SS': [
                'string',
            ],
...
    ConditionalOperator='AND'|'OR',
    ConditionExpression='string',
    ExpressionAttributeNames={
        'string': 'string'
    },
...
)

EXPERT

iBehr

answered 3 months ago

EXPERT

Leeroy Hannigan

reviewed 3 months ago

Didier_Durand · Answer

Hi,

This sample (adapted to your specific needs) should work for you:

```
try:
    table.put_item(
        Item={
            'foo':1,
            'bar':2,
        },
        ConditionExpression='attribute_not_exists(foo) AND attribute_not_exists(bar)'
    )
except botocore.exceptions.ClientError as e:
    # Ignore the ConditionalCheckFailedException, bubble up
    # other exceptions.
    if e.response['Error']['Code'] != 'ConditionalCheckFailedException':
        raise
```

Best,

Didier

boto3: where is attribute_not_exists function documented?

Relevant content