How do you query for a non-existent (null) attribute in DynamoDB

Question

I\'m trying to query a DynamoDB table to find all items where the email attribute is not set. A global secondary index called EmailPasswordIndex ex

Answer 1

@jaredHatfield is correct if the field does not exist but that will not work if the filed is null. NULL is a keyword and can't used directly. But you can use it with ExpressionAttributeValues.

const params = {
    TableName: "Accounts",
    FilterExpression: "attribute_not_exists(email) or email = :null",
    ExpressionAttributeValues: {
        ':null': null
    }
}

dynamodb.scan(params, (err, data) => {
    if (err)
        console.log(JSON.stringify(err, null, 2));
    else
        console.log(JSON.stringify(data, null, 2));
})

Answer 2

DynamoDB's Global Secondary Indexes allow for the indexes to be sparse. That means that if you have a GSI whose hash or range key for an item is not defined then that item will simply not be included in the GSI. This is useful in a number of use cases as it allows you to directly identify records that contain certain fields. However, this approach will not work if you are looking for the lack of a field.

To get all of the items that have a field not set your best bet may be resorting to a scan with a filter. This operation will be very expensive but it would be straightforward code looking something like the following:

var params = {
    TableName: "Accounts",
    FilterExpression: "attribute_not_exists(email)"
};

dynamodb.scan(params, {
    if (err)
        console.log(JSON.stringify(err, null, 2));
    else
        console.log(JSON.stringify(data, null, 2));
});