CODEWITHSUNDEEP
aws-lambdaamazon-dynamodb
Aidan Davis
Aidan Davis

Reputation: 75

What happens if you do a get item in DynamoDb using a projection expression, if the attribute in the expression may not exist

Inside a lambda, I'm calling getItem on a a table with a projection expression for a single field. This is working fine.

const usersTableParams = {
  TableName: 'users',
  Key: {
    'user-name': { S: userID }
  },
  ProjectionExpression: 'notificationEndpointARN'
};

ddb.getItem(usersTableParams, function (err, data) {
  if (err) {
    console.log('error getting user info', err);
  }
  else {
    // success
    // code...
  }
});

Now I want to add another attribute to the projection expression, but that attribute might not exist yet on the item. (If it doesn't exist I will add it at the end of the function).

Does the function fail, does it return null for that attribute, does it not return that attribute at all?

I can't find the answer in the documentation or in any google searches.

Upvotes: 0

Views: 4127

Answers (1)

Nishu Tayal
Nishu Tayal

Reputation: 20840

If Projection-Expression contains an attribute that doesn't exist in the table, it doesn't throw any error or return null.

It will simply not appear in the result and return the remaining found attributes .

cli> aws dynamodb get-item --table-name my-DynamoDBTable-I3BL7EX05JQR --key file://test.json --projection-expression "data_type,ts,username"  
{
    "Item": {
        "ts": {
            "N": "1600755209826"
        },
        "data_type": {
            "S": "Int32"
        }
    }
}

You can refer this for details: https://docs.aws.amazon.com/cli/latest/reference/dynamodb/get-item.html

Upvotes: 3

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