AWS SDK Version 3 for .NET
API Reference

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Container for the parameters to the BatchGetItem operation. 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 ProjectionExpression 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.

Inheritance Hierarchy

System.Object
  Amazon.Runtime.AmazonWebServiceRequest
    Amazon.DynamoDBv2.AmazonDynamoDBRequest
      Amazon.DynamoDBv2.Model.BatchGetItemRequest

Namespace: Amazon.DynamoDBv2.Model
Assembly: AWSSDK.DynamoDBv2.dll
Version: 3.x.y.z

Syntax

C#
public class BatchGetItemRequest : AmazonDynamoDBRequest
         IAmazonWebServiceRequest

The BatchGetItemRequest type exposes the following members

Constructors

NameDescription
Public Method BatchGetItemRequest()

Empty constructor used to set properties independently even when a simple constructor is available

Public Method BatchGetItemRequest(Dictionary<String, KeysAndAttributes>)

Instantiates BatchGetItemRequest with the parameterized properties

Public Method BatchGetItemRequest(Dictionary<String, KeysAndAttributes>, ReturnConsumedCapacity)

Instantiates BatchGetItemRequest with the parameterized properties

Properties

NameTypeDescription
Public Property RequestItems System.Collections.Generic.Dictionary<System.String, Amazon.DynamoDBv2.Model.KeysAndAttributes>

Gets and sets the property RequestItems.

A map of one or more table names and, for each table, a map that describes one or more items to retrieve from that table. Each table name can be used only once per BatchGetItem request.

Each element in the map of items to retrieve consists of the following:

  • ConsistentRead - If true, a strongly consistent read is used; if false (the default), an eventually consistent read is used.

  • ExpressionAttributeNames - One or more substitution tokens for attribute names in the ProjectionExpression parameter. The following are some use cases for using ExpressionAttributeNames:

    • To access an attribute whose name conflicts with a DynamoDB reserved word.

    • To create a placeholder for repeating occurrences of an attribute name in an expression.

    • To prevent special characters in an attribute name from being misinterpreted in an expression.

    Use the # character in an expression to dereference an attribute name. For example, consider the following attribute name:

    • Percentile

    The name of this attribute conflicts with a reserved word, so it cannot be used directly in an expression. (For the complete list of reserved words, see Reserved Words in the Amazon DynamoDB Developer Guide). To work around this, you could specify the following for ExpressionAttributeNames:

    • {"#P":"Percentile"}

    You could then use this substitution in an expression, as in this example:

    • #P = :val

    Tokens that begin with the : character are expression attribute values, which are placeholders for the actual value at runtime.

    For more information on expression attribute names, see Accessing Item Attributes in the Amazon DynamoDB Developer Guide.

  • Keys - An array of primary key attribute values that define specific items in the table. For each primary key, you must provide all of the key attributes. For example, with a simple primary key, you only need to provide the partition key value. For a composite key, you must provide both the partition key value and the sort key value.

  • ProjectionExpression - A string that identifies one or more attributes to retrieve from the table. These attributes can include scalars, sets, or elements of a JSON document. The attributes in the expression must be separated by commas.

    If no attribute names are specified, then all attributes will be returned. If any of the requested attributes are not found, they will not appear in the result.

    For more information, see Accessing Item Attributes in the Amazon DynamoDB Developer Guide.

  • AttributesToGet - This is a legacy parameter. Use ProjectionExpression instead. For more information, see AttributesToGet in the Amazon DynamoDB Developer Guide.

Public Property ReturnConsumedCapacity Amazon.DynamoDBv2.ReturnConsumedCapacity

Gets and sets the property ReturnConsumedCapacity.

Examples

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 attributesToGet = new List { "Author", "Title", "Year" };
List> sampleTableKeys = new List>
{
    new Dictionary
    {
        { "Author", new AttributeValue { S = "Mark Twain" } },
        { "Title", new AttributeValue { S = "The Adventures of Tom Sawyer" } }
    },
    new Dictionary
    {
        { "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> authorsTableKeys = new List>
{
    new Dictionary
    {
        { "Author", new AttributeValue { S = "Mark Twain" } },
    },
    new Dictionary
    {
        { "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 requestItems = new Dictionary();
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>> responses = result.Responses;
    foreach (string tableName in responses.Keys)
    {
        // Get items for each table
        List> tableItems = responses[tableName];

        // View items
        foreach (Dictionary 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.Join(", ", keyValuePair.Value.NS ?? new List()));
            }
        }
    }

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

Dictionary>> responses = response.Responses;
List consumedCapacity = response.ConsumedCapacity;

            

Version Information

.NET Standard:
Supported in: 1.3

.NET Framework:
Supported in: 4.5, 4.0, 3.5

Portable Class Library:
Supported in: Windows Store Apps
Supported in: Windows Phone 8.1
Supported in: Xamarin Android
Supported in: Xamarin iOS (Unified)
Supported in: Xamarin.Forms

Unity:
Supported Versions: 4.6 and above
Supported Platforms: Android, iOS, Standalone