AWS Dynamodb Scan | Scan if exists column values

Question

I have a table that has a column called "items", but not all rows have it, so I want to scan all rows that have "items".

Something like:

$resposta = $clientDB->scan(array(
    'TableName' => 'tableName',
    'Key' => [
        'items' => ['S' => 'exists']
    ]
));

But I can't figure out how to do it...

The table has 10000 rows, but only 10 of them have "items", and I want to get only these 10 rows.

Edit:

As Seth Geoghegan pointed below, it was necessary create a global secondary indexes on the attribute i wanted to filter.

I ended up here:

    $params = [
        'TableName' => 'tableName',
        'FilterExpression' => "attribute_exists(items)"
    ];

OR

    $params = [
        'TableName' => 'tableName',
        'FilterExpression' => 'items != :null',
        'ExpressionAttributeValues' =>  [
            ':null' => null,
        ],
    ];

But both didnt worked... First one seens necessary ExpressionAttributeValues to be setup and the second the php stop working with no error logs.

Seth Geoghegan · Accepted Answer · 2021-11-24 19:55:19Z

2

This is a perfect use case for global secondary indexes (GSI)!

You can create a GSI on the items attribute. Items with the items attribute defined will get projected into the GSI. Importantly, items that do not contain this attribute will not be in the index. You could then query the GSI and retrieve the items you're after.

answered Nov 24, 2021 at 19:55

Seth Geoghegan

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1 Comment

Lucas Martini Over a year ago

i will try that and see if's gonna work

Lucas Martini · Accepted Answer · 2021-11-30 19:37:25Z

1

Well, after some effort, i found a way though:

    $resposta = $clientDB->scan(array(
        'TableName' => 'tableName',
        'FilterExpression' => "attribute_exists(items)"
    ));

After i created another global secondary index (GSI) for "items" (pointed by Seth Geoghegan), i just needed to add in the scan function the FilterExpression the "attribute_exists(items") and it worked.

answered Nov 30, 2021 at 19:37

Lucas Martini

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