Passing a null AttributeValue into DynamoDb using AWS low level API

Question

I'm attempting to update an item within a DynamoDB table using the C# low-level API as documented here

Here is my attempt at achieving this:

var response = DynamoClientProvider.Current.UpdateItem(new UpdateItemRequest
{
    TableName = "MyTable",
    Key = {{"TableId", new AttributeValue {S = "12345"}}},
    ExpressionAttributeNames =
    {
        {"#T","Timestamp"},
        {"#D","Data"}
        {"#K","MyKey"}
    },
    ExpressionAttributeValues =
    {
        {":Timestamp", new AttributeValue("2016-2-3 00:00:00.000")},
        {":Data", new AttributeValue("some data")}
        {":MyKey", new AttributeValue("some other data")}
    },
    UpdateExpression = "SET #D = :Data, #T = :Timestamp, #K = :MyKey",
    ConditionExpression = "attribute_not_exists (Data)",
    ReturnValues = ReturnValue.ALL_OLD
});

This code works just fine, however there is an issue when MyKey is an empty string. When this is empty, I get the following error:

Amazon.DynamoDBv2.AmazonDynamoDBException: ExpressionAttributeValues contains invalid value: Supplied AttributeValue is empty, must contain exactly one of the supported datatypes for key :MyKey

I have therefore attempted to therefore pass in a null AttributeValue in order to delete the attribute in this case by setting it to the following:

new AttributeValue{NULL = true}

However this instead will set the value to be the string literal of True

prestomation prestomation · Accepted Answer · 2016-02-03T23:05:41

I'm not sure DynamoDB's types are nullable.

If you need to delete the attribute use 'SET #D = :Data, #T = :Timestamp REMOVE #K'

Passing a null AttributeValue into DynamoDb using AWS low level API

1 Answers