Amazon.DynamoDBv2.AmazonDynamoDBClient.BatchGetItem C# (CSharp) Method

BatchGetItem() public method

The BatchGetItem operation returns the attributes of one or more items from one or more tables. You identify requested items by primary key.

A single operation can retrieve up to 16 MB of data, which can contain as many as 100 items. BatchGetItem will return a partial result if the response size limit is exceeded, the table's provisioned throughput is exceeded, or an internal processing failure occurs. If a partial result is returned, the operation returns a value for UnprocessedKeys. You can use this value to retry the operation starting with the next item to get.

If you request more than 100 items BatchGetItem will return a ValidationException with the message "Too many items requested for the BatchGetItem call".

For example, if you ask to retrieve 100 items, but each individual item is 300 KB in size, the system returns 52 items (so as not to exceed the 16 MB limit). It also returns an appropriate UnprocessedKeys value so you can get the next page of results. If desired, your application can include its own logic to assemble the pages of results into one data set.

If none of the items can be processed due to insufficient provisioned throughput on all of the tables in the request, then BatchGetItem will return a ProvisionedThroughputExceededException. If at least one of the items is successfully processed, then BatchGetItem completes successfully, while returning the keys of the unread items in UnprocessedKeys.

If DynamoDB returns any unprocessed items, you should retry the batch operation on those items. However, we strongly recommend that you use an exponential backoff algorithm. If you retry the batch operation immediately, the underlying read or write requests can still fail due to throttling on the individual tables. If you delay the batch operation using exponential backoff, the individual requests in the batch are much more likely to succeed.

For more information, see Batch Operations and Error Handling in the Amazon DynamoDB Developer Guide.

By default, BatchGetItem performs eventually consistent reads on every table in the request. If you want strongly consistent reads instead, you can set ConsistentRead to true for any or all tables.

In order to minimize response latency, BatchGetItem retrieves items in parallel.

When designing your application, keep in mind that DynamoDB does not return items in any particular order. To help parse the response by item, include the primary key values for the items in your request in the AttributesToGet parameter.

If a requested item does not exist, it is not returned in the result. Requests for nonexistent items consume the minimum read capacity units according to the type of read. For more information, see Capacity Units Calculations in the Amazon DynamoDB Developer Guide.

/// An error occurred on the server side. /// /// Your request rate is too high. The AWS SDKs for DynamoDB automatically retry requests /// that receive this exception. Your request is eventually successful, unless your retry /// queue is too large to finish. Reduce the frequency of requests and use exponential /// backoff. For more information, go to Error /// Retries and Exponential Backoff in the Amazon DynamoDB Developer Guide. /// /// The operation tried to access a nonexistent table or index. The resource might not /// be specified correctly, or its status might not be ACTIVE. ///
public BatchGetItem ( BatchGetItemRequest request ) : BatchGetItemResponse
request Amazon.DynamoDBv2.Model.BatchGetItemRequest Container for the necessary parameters to execute the BatchGetItem service method.
return Amazon.DynamoDBv2.Model.BatchGetItemResponse
        public BatchGetItemResponse BatchGetItem(BatchGetItemRequest request)
        {
            var marshaller = new BatchGetItemRequestMarshaller();
            var unmarshaller = BatchGetItemResponseUnmarshaller.Instance;

            return Invoke<BatchGetItemRequest,BatchGetItemResponse>(request, marshaller, unmarshaller);
        }

Same methods

AmazonDynamoDBClient::BatchGetItem ( KeysAndAttributes>.Dictionary requestItems ) : BatchGetItemResponse
AmazonDynamoDBClient::BatchGetItem ( KeysAndAttributes>.Dictionary requestItems, ReturnConsumedCapacity returnConsumedCapacity ) : BatchGetItemResponse

Usage Example

Example #1
0
        public void BatchSamples()
        {
            EnsureTables();

            {
                #region BatchGet Sample 1

                // 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
                };

                #endregion

                #region BatchGet Sample 2

                // 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,
                };

                #endregion

                #region BatchGet Sample 3

                // 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);

                #endregion
            }


            {
                #region BatchWrite Sample 1

                // Create items to put into first table
                Dictionary<string, AttributeValue> item1 = new Dictionary<string, AttributeValue>();
                item1["Author"] = new AttributeValue { S = "Mark Twain" };
                item1["Title"] = new AttributeValue { S = "A Connecticut Yankee in King Arthur's Court" };
                item1["Pages"] = new AttributeValue { N = "575" };
                Dictionary<string, AttributeValue> item2 = new Dictionary<string, AttributeValue>();
                item2["Author"] = new AttributeValue { S = "Booker Taliaferro Washington" };
                item2["Title"] = new AttributeValue { S = "My Larger Education" };
                item2["Pages"] = new AttributeValue { N = "313" };
                item2["Year"] = new AttributeValue { N = "1911" };

                // Create key for item to delete from first table
                //  Hash-key of the target item is string value "Mark Twain"
                //  Range-key of the target item is string value "Tom Sawyer, Detective"
                Dictionary<string, AttributeValue> keyToDelete1 = new Dictionary<string, AttributeValue>
                {
                    { "Author", new AttributeValue { S = "Mark Twain" } },
                    { "Title", new AttributeValue { S = "Tom Sawyer, Detective" } }
                };

                // Construct write-request for first table
                List<WriteRequest> sampleTableItems = new List<WriteRequest>();
                sampleTableItems.Add(new WriteRequest
                {
                    PutRequest = new PutRequest { Item = item1 }
                });
                sampleTableItems.Add(new WriteRequest
                {
                    PutRequest = new PutRequest { Item = item2 }
                });
                sampleTableItems.Add(new WriteRequest
                {
                    DeleteRequest = new DeleteRequest { Key = keyToDelete1 }
                });

                #endregion

                #region BatchWrite Sample 2

                // Create key for item to delete from second table
                //  Hash-key of the target item is string value "Francis Scott Key Fitzgerald"
                Dictionary<string, AttributeValue> keyToDelete2 = new Dictionary<string, AttributeValue>
                {
                    { "Author", new AttributeValue { S = "Francis Scott Key Fitzgerald" } },
                };

                // Construct write-request for first table
                List<WriteRequest> authorsTableItems = new List<WriteRequest>();
                authorsTableItems.Add(new WriteRequest
                {
                    DeleteRequest = new DeleteRequest { Key = keyToDelete2 }
                });

                #endregion

                #region BatchWrite Sample 3

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

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

                BatchWriteItemRequest request = new BatchWriteItemRequest { RequestItems = requestItems };
                BatchWriteItemResult result;
                do
                {
                    // Issue request and retrieve items
                    result = client.BatchWriteItem(request);

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

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

                #endregion
            }
        }