BatchGetItemRequest

The following examples show how to batch get item from two tables.

This example will construct the collection of keys for the items to retrieve from the first table.

BatchGet sample - First table

// Define attributes to get and keys to retrieve
List<string> attributesToGet = new List<string> { "Author", "Title", "Year" };
List<Dictionary<string, AttributeValue>> sampleTableKeys = new List<Dictionary<string, AttributeValue>>
{
    new Dictionary<string, AttributeValue>
    {
        { "Author", new AttributeValue { S = "Mark Twain" } },
        { "Title", new AttributeValue { S = "The Adventures of Tom Sawyer" } }
    },
    new Dictionary<string, AttributeValue>
    {
        { "Author", new AttributeValue { S = "Mark Twain" } },
        { "Title", new AttributeValue { S = "Adventures of Huckleberry Finn" } }
    }
};

// Construct get-request for first table
KeysAndAttributes sampleTableItems = new KeysAndAttributes
{
    AttributesToGet = attributesToGet,
    Keys = sampleTableKeys
};

                

This example will construct the collection of keys for the items to retrieve from the second table.

BatchGet sample - Second table

// Define keys to retrieve
List<Dictionary<string, AttributeValue>> authorsTableKeys = new List<Dictionary<string, AttributeValue>>
{
    new Dictionary<string, AttributeValue>
    {
        { "Author", new AttributeValue { S = "Mark Twain" } },
    },
    new Dictionary<string, AttributeValue>
    {
        { "Author", new AttributeValue { S = "Booker Taliaferro Washington" } },
    }
};

// Construct get-request for second table
//  Skip setting AttributesToGet property to retrieve all attributes
KeysAndAttributes authorsTableItems = new KeysAndAttributes
{
    Keys = authorsTableKeys,
};

                

This example will construct the BatchGet request from the two earlier-created collections, will issue the call and in case some items are not processed, will attempt to retrieve the remaining items.

BatchGet sample - Service calls

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

// Construct table-keys mapping
Dictionary<string, KeysAndAttributes> requestItems = new Dictionary<string, KeysAndAttributes>();
requestItems["SampleTable"] = sampleTableItems;
requestItems["AuthorsTable"] = authorsTableItems;

// Construct request
BatchGetItemRequest request = new BatchGetItemRequest
{
    RequestItems = requestItems
};

BatchGetItemResult result;
do
{
    // Issue request and retrieve items
    result = client.BatchGetItem(request);

    // Iterate through responses
    Dictionary<string, List<Dictionary<string, AttributeValue>>> responses = result.Responses;
    foreach (string tableName in responses.Keys)
    {
        // Get items for each table
        List<Dictionary<string, AttributeValue>> tableItems = responses[tableName];

        // View items
        foreach (Dictionary<string, AttributeValue> item in tableItems)
        {
            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>()));
            }
        }
    }

    // Some items may not have been retrieved!
    //  Set RequestItems to the result's UnprocessedKeys and reissue request
    request.RequestItems = result.UnprocessedKeys;

} while (result.UnprocessedKeys.Count > 0);

                

batch-get-item

var client = new AmazonDynamoDBClient();
var response = client.BatchGetItem(new BatchGetItemRequest 
{
    RequestItems = new Dictionary<string, KeysAndAttributes> {
        { "tablename1", new KeysAndAttributes {
            Keys = new List<Dictionary<string, AttributeValue>> {
                new Dictionary<string, AttributeValue> {
                    { "key1", new AttributeValue { N = "NumberAttributeValue" } }
                }
            },
            AttributesToGet = new List<string> {
                "attr1",
                "attr2"
            },
            ConsistentRead = true,
            ProjectionExpression = "str1",
            ExpressionAttributeNames = new Dictionary<string, string> {
                { "name1", "attr3" },
                { "name2", "attr4" }
            }
        } },
        { "tablename2", new KeysAndAttributes {
            Keys = new List<Dictionary<string, AttributeValue>> {
                new Dictionary<string, AttributeValue> {
                    { "key2", new AttributeValue { BOOL = true } }
                }
            },
            AttributesToGet = new List<string> {
                "attr1",
                "attr2"
            },
            ConsistentRead = false,
            ProjectionExpression = "str2",
            ExpressionAttributeNames = new Dictionary<string, string> {
                { "name1", "attr3" },
                { "name2", "attr4" }
            }
        } }
    },
    ReturnConsumedCapacity = "NONE"
});

Dictionary<string, List<Dictionary<string, AttributeValue>>> responses = response.Responses;
List<ConsumedCapacity> consumedCapacity = response.ConsumedCapacity;