DynamoDB update a field which has a JSON as value with integer/num-string as keys in python

Question

I am storing an item with the following structure in my dynamodb table.

Item = {"response": [
    {
        "answers": {
            "11-18": 0,
            "19-24": 0
        }
    }
]}

I want to update response[0].answers.11-18 incrementally. My command was:

table_resource.update_item(
        Key={
            'id': 123
        },
        UpdateExpression="set response[0].answers.11-18 = response[0].answers.11-18 + :inc",
        ExpressionAttributeValues={":inc": 1},
        ReturnValues="UPDATED_NEW",
)

I get the following error.

An error occurred (ValidationException) when calling the UpdateItem operation: Invalid UpdateExpression: Syntax error; token: "11", near: ".11-"

Matthew Pope · Accepted Answer · 2018-11-21 21:01:26Z

2

Your nested attribute 11-18 begins with a number, so you can’t use it in an update expression.

If an attribute name begins with a number or contains a space, a special character, or a reserved word, then you must use an expression attribute name to replace that attribute's name in the expression.

You can work around this by using placeholder ExpressionAttributeNames.

answered Nov 21, 2018 at 21:01

Matthew Pope

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2 Comments

Mehran Over a year ago

Would it create problems if the nested attribute did not begin with a number when I'm using an ExpressionAttributeName?

Matthew Pope Over a year ago

No. You can use safely use ExpressionAttributeNames for any or every attribute.

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