AmazonDynamoDBClient.Scan (ScanRequest)

The following example shows how to scan items in a table.
Note: the Scan operation goes through every item in the table to check if the item matches all the scan conditions. This makes the Scan operation particularly slow and expensive (in terms of provisioned throughput).
We will now retrieve all items where the Pages attribute is greater than the numerical value "200" and where the Title attribute contains the string "Adventures".

Scan sample

// Create a client
AmazonDynamoDBClient client = new AmazonDynamoDBClient();

// Define scan conditions
Dictionary<string, Condition> conditions = new Dictionary<string, Condition>();

// Title attribute should contain the string "Adventures"
Condition titleCondition = new Condition();
titleCondition.ComparisonOperator = ComparisonOperator.CONTAINS;
titleCondition.AttributeValueList.Add(new AttributeValue { S = "Adventures" });
conditions["Title"] = titleCondition;

// Pages attributes must be greater-than the numeric value "200"
Condition pagesCondition = new Condition();
pagesCondition.ComparisonOperator = ComparisonOperator.GT;
pagesCondition.AttributeValueList.Add(new AttributeValue { N = "200" });
conditions["Pages"] = pagesCondition;


// Define marker variable
Dictionary<string, AttributeValue> startKey = null;

do
{
    // Create Scan request
    ScanRequest request = new ScanRequest
    {
        TableName = "SampleTable",
        ExclusiveStartKey = startKey,
        ScanFilter = conditions
    };

    // Issue request
    ScanResult result = client.Scan(request);

    // View all returned items
    List<Dictionary<string, AttributeValue>> items = result.Items;
    foreach (Dictionary<string, AttributeValue> item in items)
    {
        Console.WriteLine("Item:");
        foreach (var keyValuePair in item)
        {
            Console.WriteLine("{0} : S={1}, N={2}, SS=[{3}], NS=[{4}]",
                keyValuePair.Key,
                keyValuePair.Value.S,
                keyValuePair.Value.N,
                string.Join(", ", keyValuePair.Value.SS ?? new List<string>()),
                string.Join(", ", keyValuePair.Value.NS ?? new List<string>()));
        }
    }

    // Set marker variable
    startKey = result.LastEvaluatedKey;
} while (startKey != null && startKey.Count > 0);

                

The following example shows how we can utilize parallel scan to partition a table into 10 segments and scan each segment in a separate thread.
To avoid resource contention between threads, the results will be written into 10 separate files. Each segment will have a file of its own.

Parallel scan sample

// Create a client
AmazonDynamoDBClient client = new AmazonDynamoDBClient();

// Define scan conditions
Dictionary<string, Condition> conditions = new Dictionary<string, Condition>();

// Pages attributes must be greater-than the numeric value "200"
Condition pagesCondition = new Condition();
pagesCondition.ComparisonOperator = ComparisonOperator.GT;
pagesCondition.AttributeValueList.Add(new AttributeValue { N = "200" });
conditions["Pages"] = pagesCondition;

// Setup 10 simultaneous threads, each thread calling Scan operation
// with its own segment value.
int totalSegments = 10;
Parallel.For(0, totalSegments, segment =>
{
    // Define marker variable
    Dictionary<string, AttributeValue> startKey = null;

    do
    {
        // Create Scan request
        ScanRequest request = new ScanRequest
        {
            TableName = "SampleTable",
            ExclusiveStartKey = startKey,
            ScanFilter = conditions,
            // Total segments to split the table into
            TotalSegments = totalSegments,
            // Current segment to scan
            Segment = segment
        };

        // Issue request
        var result = client.Scan(request);

        // Write returned items to file
        string path = string.Format("ParallelScan-{0}-of-{1}.txt", totalSegments, segment);
        List<Dictionary<string, AttributeValue>> items = result.Items;
        using (Stream stream = File.OpenWrite(path))
        using (StreamWriter writer = new StreamWriter(stream))
        {
            foreach (Dictionary<string, AttributeValue> item in items)
            {
                writer.WriteLine("Item:");
                foreach (var keyValuePair in item)
                {
                    writer.WriteLine("{0} : S={1}, N={2}, SS=[{3}], NS=[{4}]",
                        keyValuePair.Key,
                        keyValuePair.Value.S,
                        keyValuePair.Value.N,
                        string.Join(", ", keyValuePair.Value.SS ?? new List<string>()),
                        string.Join(", ", keyValuePair.Value.NS ?? new List<string>()));
                }
            }
        }

        // Set marker variable
        startKey = result.LastEvaluatedKey;
    } while (startKey != null && startKey.Count > 0);
});