AWS SDK を使用して DynamoDB 項目のバッチを取得する

DynamoDB 項目のバッチを取得する方法を、次のコード例により示します。

.NET

AWS SDK for .NET

注記

他にもありますGitHub。用例一覧を検索し、AWS コード例リポジトリでの設定と実行の方法を確認してください。

using System;
using System.Collections.Generic;
using Amazon.DynamoDBv2;
using Amazon.DynamoDBv2.Model;

namespace LowLevelBatchGet
{
    public class LowLevelBatchGet
    {
        private static readonly string _table1Name = "Forum";
        private static readonly string _table2Name = "Thread";

        public static async void RetrieveMultipleItemsBatchGet(AmazonDynamoDBClient client)
        {
            var request = new BatchGetItemRequest
            {
                RequestItems = new Dictionary<string, KeysAndAttributes>()
            {
                { _table1Name,
                  new KeysAndAttributes
                  {
                      Keys = new List<Dictionary<string, AttributeValue> >()
                      {
                          new Dictionary<string, AttributeValue>()
                          {
                              { "Name", new AttributeValue {
                            S = "Amazon DynamoDB"
                        } }
                          },
                          new Dictionary<string, AttributeValue>()
                          {
                              { "Name", new AttributeValue {
                            S = "Amazon S3"
                        } }
                          }
                      }
                  }},
                {
                    _table2Name,
                    new KeysAndAttributes
                    {
                        Keys = new List<Dictionary<string, AttributeValue> >()
                        {
                            new Dictionary<string, AttributeValue>()
                            {
                                { "ForumName", new AttributeValue {
                                      S = "Amazon DynamoDB"
                                  } },
                                { "Subject", new AttributeValue {
                                      S = "DynamoDB Thread 1"
                                  } }
                            },
                            new Dictionary<string, AttributeValue>()
                            {
                                { "ForumName", new AttributeValue {
                                      S = "Amazon DynamoDB"
                                  } },
                                { "Subject", new AttributeValue {
                                      S = "DynamoDB Thread 2"
                                  } }
                            },
                            new Dictionary<string, AttributeValue>()
                            {
                                { "ForumName", new AttributeValue {
                                      S = "Amazon S3"
                                  } },
                                { "Subject", new AttributeValue {
                                      S = "S3 Thread 1"
                                  } }
                            }
                        }
                    }
                }
            }
            };

            BatchGetItemResponse response;
            do
            {
                Console.WriteLine("Making request");
                response = await client.BatchGetItemAsync(request);

                // Check the response.
                var responses = response.Responses; // Attribute list in the response.

                foreach (var tableResponse in responses)
                {
                    var tableResults = tableResponse.Value;
                    Console.WriteLine("Items retrieved from table {0}", tableResponse.Key);
                    foreach (var item1 in tableResults)
                    {
                        PrintItem(item1);
                    }
                }

                // Any unprocessed keys? could happen if you exceed ProvisionedThroughput or some other error.
                Dictionary<string, KeysAndAttributes> unprocessedKeys = response.UnprocessedKeys;
                foreach (var unprocessedTableKeys in unprocessedKeys)
                {
                    // Print table name.
                    Console.WriteLine(unprocessedTableKeys.Key);
                    // Print unprocessed primary keys.
                    foreach (var key in unprocessedTableKeys.Value.Keys)
                    {
                        PrintItem(key);
                    }
                }

                request.RequestItems = unprocessedKeys;
            } while (response.UnprocessedKeys.Count > 0);
        }

        private static void PrintItem(Dictionary<string, AttributeValue> attributeList)
        {
            foreach (KeyValuePair<string, AttributeValue> kvp in attributeList)
            {
                string attributeName = kvp.Key;
                AttributeValue value = kvp.Value;

                Console.WriteLine(
                    attributeName + " " +
                    (value.S == null ? "" : "S=[" + value.S + "]") +
                    (value.N == null ? "" : "N=[" + value.N + "]") +
                    (value.SS == null ? "" : "SS=[" + string.Join(",", value.SS.ToArray()) + "]") +
                    (value.NS == null ? "" : "NS=[" + string.Join(",", value.NS.ToArray()) + "]")
                    );
            }
            Console.WriteLine("************************************************");
        }

        static void Main()
        {
            var client = new AmazonDynamoDBClient();

            RetrieveMultipleItemsBatchGet(client);
        }
    }
}

• API の詳細については、AWS SDK for .NETAPI BatchGetItemリファレンスのを参照してください。

C++

SDK for C++

注記

他にもありますGitHub。用例一覧を検索し、AWS コード例リポジトリでの設定と実行の方法を確認してください。

//! Batch get items from different Amazon DynamoDB tables.
/*!
  \sa batchGetItem()
  \param clientConfiguration: AWS client configuration.
  \return bool: Function succeeded.
 */
bool AwsDoc::DynamoDB::batchGetItem(
        const Aws::Client::ClientConfiguration &clientConfiguration) {
    Aws::DynamoDB::DynamoDBClient dynamoClient(clientConfiguration);

    Aws::DynamoDB::Model::BatchGetItemRequest request;

    // Table1: Forum.
    Aws::String table1Name = "Forum";
    Aws::DynamoDB::Model::KeysAndAttributes table1KeysAndAttributes;

    // Table1: Projection expression.
    table1KeysAndAttributes.SetProjectionExpression("#n, Category, Messages, #v");

    // Table1: Expression attribute names.
    Aws::Http::HeaderValueCollection headerValueCollection;
    headerValueCollection.emplace("#n", "Name");
    headerValueCollection.emplace("#v", "Views");
    table1KeysAndAttributes.SetExpressionAttributeNames(headerValueCollection);

    // Table1: Set key name, type, and value to search.
    std::vector<Aws::String> nameValues = {"Amazon DynamoDB", "Amazon S3"};
    for (const Aws::String &name: nameValues) {
        Aws::Map<Aws::String, Aws::DynamoDB::Model::AttributeValue> keys;
        Aws::DynamoDB::Model::AttributeValue key;
        key.SetS(name);
        keys.emplace("Name", key);
        table1KeysAndAttributes.AddKeys(keys);
    }

    Aws::Map<Aws::String, Aws::DynamoDB::Model::KeysAndAttributes> requestItems;
    requestItems.emplace(table1Name, table1KeysAndAttributes);

    // Table2: ProductCatalog.
    Aws::String table2Name = "ProductCatalog";
    Aws::DynamoDB::Model::KeysAndAttributes table2KeysAndAttributes;
    table2KeysAndAttributes.SetProjectionExpression("Title, Price, Color");

    // Table2: Set key name, type, and value to search.
    std::vector<Aws::String> idValues = {"102", "103", "201"};
    for (const Aws::String &id: idValues) {
        Aws::Map<Aws::String, Aws::DynamoDB::Model::AttributeValue> keys;
        Aws::DynamoDB::Model::AttributeValue key;
        key.SetN(id);
        keys.emplace("Id", key);
        table2KeysAndAttributes.AddKeys(keys);
    }

    requestItems.emplace(table2Name, table2KeysAndAttributes);

    bool result = true;
    do {  // Use a do loop to handle pagination.
        request.SetRequestItems(requestItems);
        const Aws::DynamoDB::Model::BatchGetItemOutcome &outcome = dynamoClient.BatchGetItem(
                request);

        if (outcome.IsSuccess()) {
            for (const auto &responsesMapEntry: outcome.GetResult().GetResponses()) {
                Aws::String tableName = responsesMapEntry.first;
                const Aws::Vector<Aws::Map<Aws::String, Aws::DynamoDB::Model::AttributeValue>> &tableResults = responsesMapEntry.second;
                std::cout << "Retrieved " << tableResults.size()
                          << " responses for table '" << tableName << "'.\n"
                          << std::endl;
                if (tableName == "Forum") {

                    std::cout << "Name | Category | Message | Views" << std::endl;
                    for (const Aws::Map<Aws::String, Aws::DynamoDB::Model::AttributeValue> &item: tableResults) {
                        std::cout << item.at("Name").GetS() << " | ";
                        std::cout << item.at("Category").GetS() << " | ";
                        std::cout << (item.count("Message") == 0 ? "" : item.at(
                                "Messages").GetN()) << " | ";
                        std::cout << (item.count("Views") == 0 ? "" : item.at(
                                "Views").GetN()) << std::endl;
                    }
                }
                else {
                    std::cout << "Title | Price | Color" << std::endl;
                    for (const Aws::Map<Aws::String, Aws::DynamoDB::Model::AttributeValue> &item: tableResults) {
                        std::cout << item.at("Title").GetS() << " | ";
                        std::cout << (item.count("Price") == 0 ? "" : item.at(
                                "Price").GetN());
                        if (item.count("Color")) {
                            std::cout << " | ";
                            for (const std::shared_ptr<Aws::DynamoDB::Model::AttributeValue> &listItem: item.at(
                                    "Color").GetL())
                                std::cout << listItem->GetS() << " ";
                        }
                        std::cout << std::endl;
                    }
                }
                std::cout << std::endl;
            }

            // If necessary, repeat request for remaining items.
            requestItems = outcome.GetResult().GetUnprocessedKeys();
        }
        else {
            std::cerr << "Batch get item failed: " << outcome.GetError().GetMessage()
                      << std::endl;
            result = false;
            break;
        }
    } while (!requestItems.empty());

    return result;
}

• API の詳細については、AWS SDK for C++API BatchGetItemリファレンスのを参照してください。

JavaScript

SDK for forJavaScript (v3)

注記

他にもありますGitHub。用例一覧を検索し、AWS コード例リポジトリでの設定と実行の方法を確認してください。

クライアントを作成します。

// Create service client module using ES6 syntax.
import { DynamoDBClient } from "@aws-sdk/client-dynamodb";
// Set the AWS Region.
const REGION = "REGION"; //e.g. "us-east-1"
// Create an Amazon DynamoDB service client object.
const ddbClient = new DynamoDBClient({ region: REGION });
export { ddbClient };

項目を取得します。

// Import required AWS SDK clients and commands for Node.js
import { BatchGetItemCommand } from "@aws-sdk/client-dynamodb";
import { ddbClient } from "./libs/ddbClient.js";

// Set the parameters
export const params = {
  RequestItems: {
    TABLE_NAME: {
      Keys: [
        {
          KEY_NAME_1: { N: "KEY_VALUE" },
          KEY_NAME_2: { N: "KEY_VALUE" },
          KEY_NAME_3: { N: "KEY_VALUE" },
        },
      ],
      ProjectionExpression: "ATTRIBUTE_NAME",
    },
  },
};

export const run = async () => {
  try {
    const data = await ddbClient.send(new BatchGetItemCommand(params));
    console.log("Success, items retrieved", data);
    return data;
  } catch (err) {
    console.log("Error", err);
  }
};
run();

• 詳細については、AWS SDK for JavaScript デベロッパーガイドを参照してください。

• API の詳細については、AWS SDK for JavaScriptAPI BatchGetItemリファレンスのを参照してください。

SDK for forJavaScript (v2)

注記

他にもありますGitHub。用例一覧を検索し、AWS コード例リポジトリでの設定と実行の方法を確認してください。

// Load the AWS SDK for Node.js
var AWS = require('aws-sdk');
// Set the region 
AWS.config.update({region: 'REGION'});

// Create DynamoDB service object
var ddb = new AWS.DynamoDB({apiVersion: '2012-08-10'});

var params = {
  RequestItems: {
    'TABLE_NAME': {
      Keys: [
        {'KEY_NAME': {N: 'KEY_VALUE_1'}},
        {'KEY_NAME': {N: 'KEY_VALUE_2'}},
        {'KEY_NAME': {N: 'KEY_VALUE_3'}}
      ],
      ProjectionExpression: 'KEY_NAME, ATTRIBUTE'
    }
  }
};

ddb.batchGetItem(params, function(err, data) {
  if (err) {
    console.log("Error", err);
  } else {
    data.Responses.TABLE_NAME.forEach(function(element, index, array) {
      console.log(element);
    });
  }
});

• 詳細については、AWS SDK for JavaScript デベロッパーガイドを参照してください。

• API の詳細については、AWS SDK for JavaScriptAPI BatchGetItemリファレンスのを参照してください。

Python

SDK for Python (Boto3)

注記

他にもありますGitHub。用例一覧を検索し、AWS コード例リポジトリでの設定と実行の方法を確認してください。

import decimal
import json
import logging
import os
import pprint
import time
import boto3
from botocore.exceptions import ClientError

logger = logging.getLogger(__name__)
dynamodb = boto3.resource('dynamodb')

MAX_GET_SIZE = 100  # Amazon DynamoDB rejects a get batch larger than 100 items.


def do_batch_get(batch_keys):
    """
    Gets a batch of items from Amazon DynamoDB. Batches can contain keys from
    more than one table.

    When Amazon DynamoDB cannot process all items in a batch, a set of unprocessed
    keys is returned. This function uses an exponential backoff algorithm to retry
    getting the unprocessed keys until all are retrieved or the specified
    number of tries is reached.

    :param batch_keys: The set of keys to retrieve. A batch can contain at most 100
                       keys. Otherwise, Amazon DynamoDB returns an error.
    :return: The dictionary of retrieved items grouped under their respective
             table names.
    """
    tries = 0
    max_tries = 5
    sleepy_time = 1  # Start with 1 second of sleep, then exponentially increase.
    retrieved = {key: [] for key in batch_keys}
    while tries < max_tries:
        response = dynamodb.batch_get_item(RequestItems=batch_keys)
        # Collect any retrieved items and retry unprocessed keys.
        for key in response.get('Responses', []):
            retrieved[key] += response['Responses'][key]
        unprocessed = response['UnprocessedKeys']
        if len(unprocessed) > 0:
            batch_keys = unprocessed
            unprocessed_count = sum(
                [len(batch_key['Keys']) for batch_key in batch_keys.values()])
            logger.info(
                "%s unprocessed keys returned. Sleep, then retry.",
                unprocessed_count)
            tries += 1
            if tries < max_tries:
                logger.info("Sleeping for %s seconds.", sleepy_time)
                time.sleep(sleepy_time)
                sleepy_time = min(sleepy_time * 2, 32)
        else:
            break

    return retrieved

• API の詳細については、「AWSSDK for Python (Boto3) API リファレンス」のを参照してくださいBatchGetItem。

Swift

SDK for Swift

注記

これはプレビューリリースの SDK に関するプレリリースドキュメントです。このドキュメントは変更される可能性があります。

注記

他にもありますGitHub。用例一覧を検索し、AWS コード例リポジトリでの設定と実行の方法を確認してください。

    /// Gets an array of `Movie` objects describing all the movies in the
    /// specified list. Any movies that aren't found in the list have no
    /// corresponding entry in the resulting array.
    ///
    /// - Parameters
    ///     - keys: An array of tuples, each of which specifies the title and
    ///       release year of a movie to fetch from the table.
    ///
    /// - Returns:
    ///     - An array of `Movie` objects describing each match found in the
    ///     table.
    ///
    /// - Throws:
    ///     - `MovieError.ClientUninitialized` if the DynamoDB client has not
    ///     been initialized.
    ///     - DynamoDB errors are thrown without change.
    func batchGet(keys: [(title: String, year: Int)]) async throws -> [Movie] {
        guard let client = self.ddbClient else {
            throw MovieError.ClientUninitialized
        }

        var movieList: [Movie] = []
        var keyItems: [[Swift.String:DynamoDBClientTypes.AttributeValue]] = []

        // Convert the list of keys into the form used by DynamoDB.

        for key in keys {
            let item: [Swift.String:DynamoDBClientTypes.AttributeValue] = [
                "title": .s(key.title),
                "year": .n(String(key.year))
            ]
            keyItems.append(item)
        }

        // Create the input record for `batchGetItem()`. The list of requested
        // items is in the `requestItems` property. This array contains one
        // entry for each table from which items are to be fetched. In this
        // example, there's only one table containing the movie data.
        //
        // If we wanted this program to also support searching for matches
        // in a table of book data, we could add a second `requestItem`
        // mapping the name of the book table to the list of items we want to
        // find in it.
        let input = BatchGetItemInput(
            requestItems: [
                self.tableName: .init(
                    consistentRead: true,
                    keys: keyItems
                )
            ]
        )

        // Fetch the matching movies from the table.

        let output = try await client.batchGetItem(input: input)

        // Get the set of responses. If there aren't any, return the empty
        // movie list.

        guard let responses = output.responses else {
            return movieList
        }

        // Get the list of matching items for the table with the name
        // `tableName`.

        guard let responseList = responses[self.tableName] else {
            return movieList
        }

        // Create `Movie` items for each of the matching movies in the table
        // and add them to the `MovieList` array.

        for response in responseList {
            movieList.append(try Movie(withItem: response))
        }

        return movieList
    }

• API の詳細については、AWSSDK for Swift API リファレンスの「発行」を参照してくださいBatchGetItem。