从 DynamoDB 表中读取项目 - Amazon DynamoDB
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从 DynamoDB 表中读取项目

您可以使用 Amazon Web Services Management Console、Amazon CLI 或 Amazon SDK 从 DynamoDB 表中读取项目。有关项目的更多信息,请参阅 Amazon DynamoDB 的核心组件

使用 Amazon SDK 从 DynamoDB 表中读取项目

以下代码示例显示如何使用 Amazon SDK 读取 DynamoDB 表中的项目。

.NET
Amazon SDK for .NET
注意

还有更多相关信息 GitHub。在 Amazon 代码示例存储库中查找完整示例,了解如何进行设置和运行。

/// <summary> /// Gets information about an existing movie from the table. /// </summary> /// <param name="client">An initialized Amazon DynamoDB client object.</param> /// <param name="newMovie">A Movie object containing information about /// the movie to retrieve.</param> /// <param name="tableName">The name of the table containing the movie.</param> /// <returns>A Dictionary object containing information about the item /// retrieved.</returns> public static async Task<Dictionary<string, AttributeValue>> GetItemAsync(AmazonDynamoDBClient client, Movie newMovie, string tableName) { var key = new Dictionary<string, AttributeValue> { ["title"] = new AttributeValue { S = newMovie.Title }, ["year"] = new AttributeValue { N = newMovie.Year.ToString() }, }; var request = new GetItemRequest { Key = key, TableName = tableName, }; var response = await client.GetItemAsync(request); return response.Item; }
  • 有关 API 的详细信息,请参阅 Amazon SDK for .NETAPI 参考GetItem中的。

Bash
Amazon CLI 及 Bash 脚本
注意

还有更多相关信息 GitHub。在 Amazon 代码示例存储库中查找完整示例,了解如何进行设置和运行。

############################################################################# # function dynamodb_get_item # # This function gets an item from a DynamoDB table. # # Parameters: # -n table_name -- The name of the table. # -k keys -- Path to json file containing the keys that identify the item to get. # [-q query] -- Optional JMESPath query expression. # # Returns: # The item as text output. # And: # 0 - If successful. # 1 - If it fails. ############################################################################ function dynamodb_get_item() { local table_name keys query response local option OPTARG # Required to use getopts command in a function. # ###################################### # Function usage explanation ####################################### function usage() { echo "function dynamodb_get_item" echo "Get an item from a DynamoDB table." echo " -n table_name -- The name of the table." echo " -k keys -- Path to json file containing the keys that identify the item to get." echo " [-q query] -- Optional JMESPath query expression." echo "" } query="" while getopts "n:k:q:h" option; do case "${option}" in n) table_name="${OPTARG}" ;; k) keys="${OPTARG}" ;; q) query="${OPTARG}" ;; h) usage return 0 ;; \?) echo "Invalid parameter" usage return 1 ;; esac done export OPTIND=1 if [[ -z "$table_name" ]]; then errecho "ERROR: You must provide a table name with the -n parameter." usage return 1 fi if [[ -z "$keys" ]]; then errecho "ERROR: You must provide a keys json file path the -k parameter." usage return 1 fi if [[ -n "$query" ]]; then response=$(aws dynamodb get-item \ --table-name "$table_name" \ --key file://"$keys" \ --output text \ --query "$query") else response=$( aws dynamodb get-item \ --table-name "$table_name" \ --key file://"$keys" \ --output text ) fi local error_code=${?} if [[ $error_code -ne 0 ]]; then aws_cli_error_log $error_code errecho "ERROR: AWS reports get-item operation failed.$response" return 1 fi if [[ -n "$query" ]]; then echo "$response" | sed "/^\t/s/\t//1" # Remove initial tab that the JMSEPath query inserts on some strings. else echo "$response" fi return 0 }

本示例中使用的实用程序函数。

############################################################################### # function errecho # # This function outputs everything sent to it to STDERR (standard error output). ############################################################################### function errecho() { printf "%s\n" "$*" 1>&2 } ############################################################################## # function aws_cli_error_log() # # This function is used to log the error messages from the AWS CLI. # # See https://docs.aws.amazon.com/cli/latest/topic/return-codes.html#cli-aws-help-return-codes. # # The function expects the following argument: # $1 - The error code returned by the AWS CLI. # # Returns: # 0: - Success. # ############################################################################## function aws_cli_error_log() { local err_code=$1 errecho "Error code : $err_code" if [ "$err_code" == 1 ]; then errecho " One or more S3 transfers failed." elif [ "$err_code" == 2 ]; then errecho " Command line failed to parse." elif [ "$err_code" == 130 ]; then errecho " Process received SIGINT." elif [ "$err_code" == 252 ]; then errecho " Command syntax invalid." elif [ "$err_code" == 253 ]; then errecho " The system environment or configuration was invalid." elif [ "$err_code" == 254 ]; then errecho " The service returned an error." elif [ "$err_code" == 255 ]; then errecho " 255 is a catch-all error." fi return 0 }
  • 有关 API 的详细信息,请参阅Amazon CLI命令参考GetItem中的。

C++
SDK for C++
注意

还有更多相关信息 GitHub。在 Amazon 代码示例存储库中查找完整示例,了解如何进行设置和运行。

//! Get an item from an Amazon DynamoDB table. /*! \sa getItem() \param tableName: The table name. \param partitionKey: The partition key. \param partitionValue: The value for the partition key. \param clientConfiguration: AWS client configuration. \return bool: Function succeeded. */ bool AwsDoc::DynamoDB::getItem(const Aws::String &tableName, const Aws::String &partitionKey, const Aws::String &partitionValue, const Aws::Client::ClientConfiguration &clientConfiguration) { Aws::DynamoDB::DynamoDBClient dynamoClient(clientConfiguration); Aws::DynamoDB::Model::GetItemRequest request; // Set up the request. request.SetTableName(tableName); request.AddKey(partitionKey, Aws::DynamoDB::Model::AttributeValue().SetS(partitionValue)); // Retrieve the item's fields and values. const Aws::DynamoDB::Model::GetItemOutcome &outcome = dynamoClient.GetItem(request); if (outcome.IsSuccess()) { // Reference the retrieved fields/values. const Aws::Map<Aws::String, Aws::DynamoDB::Model::AttributeValue> &item = outcome.GetResult().GetItem(); if (!item.empty()) { // Output each retrieved field and its value. for (const auto &i: item) std::cout << "Values: " << i.first << ": " << i.second.GetS() << std::endl; } else { std::cout << "No item found with the key " << partitionKey << std::endl; } } else { std::cerr << "Failed to get item: " << outcome.GetError().GetMessage(); } return outcome.IsSuccess(); }
  • 有关 API 的详细信息,请参阅 Amazon SDK for C++API 参考GetItem中的。

CLI
Amazon CLI

示例 1:读取表中的项目

以下get-item示例从MusicCollection表中检索一个项目。该表具有 hash-and-range 主键(ArtistSongTitle),因此必须同时指定这两个属性。该命令还请求有关该操作消耗的读取容量的信息。

aws dynamodb get-item \ --table-name MusicCollection \ --key file://key.json \ --return-consumed-capacity TOTAL

key.json 的内容:

{ "Artist": {"S": "Acme Band"}, "SongTitle": {"S": "Happy Day"} }

输出:

{ "Item": { "AlbumTitle": { "S": "Songs About Life" }, "SongTitle": { "S": "Happy Day" }, "Artist": { "S": "Acme Band" } }, "ConsumedCapacity": { "TableName": "MusicCollection", "CapacityUnits": 0.5 } }

有关更多信息,请参阅亚马逊 DynamoD B 开发者指南中的阅读项目

示例 2:使用一致性读取来读取项目

以下示例使用强一致性读取从MusicCollection表中检索项目。

aws dynamodb get-item \ --table-name MusicCollection \ --key file://key.json \ --consistent-read \ --return-consumed-capacity TOTAL

key.json 的内容:

{ "Artist": {"S": "Acme Band"}, "SongTitle": {"S": "Happy Day"} }

输出:

{ "Item": { "AlbumTitle": { "S": "Songs About Life" }, "SongTitle": { "S": "Happy Day" }, "Artist": { "S": "Acme Band" } }, "ConsumedCapacity": { "TableName": "MusicCollection", "CapacityUnits": 1.0 } }

有关更多信息,请参阅亚马逊 DynamoD B 开发者指南中的阅读项目

示例 3:检索项目的特定属性

以下示例使用投影表达式仅检索所需项目的三个属性。

aws dynamodb get-item \ --table-name ProductCatalog \ --key '{"Id": {"N": "102"}}' \ --projection-expression "#T, #C, #P" \ --expression-attribute-names file://names.json

names.json 的内容:

{ "#T": "Title", "#C": "ProductCategory", "#P": "Price" }

输出:

{ "Item": { "Price": { "N": "20" }, "Title": { "S": "Book 102 Title" }, "ProductCategory": { "S": "Book" } } }

有关更多信息,请参阅亚马逊 DynamoD B 开发者指南中的阅读项目

  • 有关 API 的详细信息,请参阅Amazon CLI命令参考GetItem中的。

Go
适用于 Go V2 的 SDK
注意

还有更多相关信息 GitHub。在 Amazon 代码示例存储库中查找完整示例,了解如何进行设置和运行。

// TableBasics encapsulates the Amazon DynamoDB service actions used in the examples. // It contains a DynamoDB service client that is used to act on the specified table. type TableBasics struct { DynamoDbClient *dynamodb.Client TableName string } // GetMovie gets movie data from the DynamoDB table by using the primary composite key // made of title and year. func (basics TableBasics) GetMovie(title string, year int) (Movie, error) { movie := Movie{Title: title, Year: year} response, err := basics.DynamoDbClient.GetItem(context.TODO(), &dynamodb.GetItemInput{ Key: movie.GetKey(), TableName: aws.String(basics.TableName), }) if err != nil { log.Printf("Couldn't get info about %v. Here's why: %v\n", title, err) } else { err = attributevalue.UnmarshalMap(response.Item, &movie) if err != nil { log.Printf("Couldn't unmarshal response. Here's why: %v\n", err) } } return movie, err } // Movie encapsulates data about a movie. Title and Year are the composite primary key // of the movie in Amazon DynamoDB. Title is the sort key, Year is the partition key, // and Info is additional data. type Movie struct { Title string `dynamodbav:"title"` Year int `dynamodbav:"year"` Info map[string]interface{} `dynamodbav:"info"` } // GetKey returns the composite primary key of the movie in a format that can be // sent to DynamoDB. func (movie Movie) GetKey() map[string]types.AttributeValue { title, err := attributevalue.Marshal(movie.Title) if err != nil { panic(err) } year, err := attributevalue.Marshal(movie.Year) if err != nil { panic(err) } return map[string]types.AttributeValue{"title": title, "year": year} } // String returns the title, year, rating, and plot of a movie, formatted for the example. func (movie Movie) String() string { return fmt.Sprintf("%v\n\tReleased: %v\n\tRating: %v\n\tPlot: %v\n", movie.Title, movie.Year, movie.Info["rating"], movie.Info["plot"]) }
  • 有关 API 的详细信息,请参阅 Amazon SDK for GoAPI 参考GetItem中的。

Java
SDK for Java 2.x
注意

还有更多相关信息 GitHub。在 Amazon 代码示例存储库中查找完整示例,了解如何进行设置和运行。

使用从表中获取项目 DynamoDbClient。

import software.amazon.awssdk.regions.Region; import software.amazon.awssdk.services.dynamodb.model.DynamoDbException; import software.amazon.awssdk.services.dynamodb.DynamoDbClient; import software.amazon.awssdk.services.dynamodb.model.AttributeValue; import software.amazon.awssdk.services.dynamodb.model.GetItemRequest; import java.util.HashMap; import java.util.Map; import java.util.Set; /** * Before running this Java V2 code example, set up your development * environment, including your credentials. * * For more information, see the following documentation topic: * * https://docs.aws.amazon.com/sdk-for-java/latest/developer-guide/get-started.html * * To get an item from an Amazon DynamoDB table using the AWS SDK for Java V2, * its better practice to use the * Enhanced Client, see the EnhancedGetItem example. */ public class GetItem { public static void main(String[] args) { final String usage = """ Usage: <tableName> <key> <keyVal> Where: tableName - The Amazon DynamoDB table from which an item is retrieved (for example, Music3).\s key - The key used in the Amazon DynamoDB table (for example, Artist).\s keyval - The key value that represents the item to get (for example, Famous Band). """; if (args.length != 3) { System.out.println(usage); System.exit(1); } String tableName = args[0]; String key = args[1]; String keyVal = args[2]; System.out.format("Retrieving item \"%s\" from \"%s\"\n", keyVal, tableName); Region region = Region.US_EAST_1; DynamoDbClient ddb = DynamoDbClient.builder() .region(region) .build(); getDynamoDBItem(ddb, tableName, key, keyVal); ddb.close(); } public static void getDynamoDBItem(DynamoDbClient ddb, String tableName, String key, String keyVal) { HashMap<String, AttributeValue> keyToGet = new HashMap<>(); keyToGet.put(key, AttributeValue.builder() .s(keyVal) .build()); GetItemRequest request = GetItemRequest.builder() .key(keyToGet) .tableName(tableName) .build(); try { // If there is no matching item, GetItem does not return any data. Map<String, AttributeValue> returnedItem = ddb.getItem(request).item(); if (returnedItem.isEmpty()) System.out.format("No item found with the key %s!\n", key); else { Set<String> keys = returnedItem.keySet(); System.out.println("Amazon DynamoDB table attributes: \n"); for (String key1 : keys) { System.out.format("%s: %s\n", key1, returnedItem.get(key1).toString()); } } } catch (DynamoDbException e) { System.err.println(e.getMessage()); System.exit(1); } } }
  • 有关 API 的详细信息,请参阅 Amazon SDK for Java 2.xAPI 参考GetItem中的。

JavaScript
适用于 JavaScript (v3) 的软件开发工具包
注意

还有更多相关信息 GitHub。在 Amazon 代码示例存储库中查找完整示例,了解如何进行设置和运行。

此示例使用文档客户端来简化在 DynamoDB 中处理项目的过程。有关 API 的详细信息,请参阅GetCommand

import { DynamoDBClient } from "@aws-sdk/client-dynamodb"; import { DynamoDBDocumentClient, GetCommand } from "@aws-sdk/lib-dynamodb"; const client = new DynamoDBClient({}); const docClient = DynamoDBDocumentClient.from(client); export const main = async () => { const command = new GetCommand({ TableName: "AngryAnimals", Key: { CommonName: "Shoebill", }, }); const response = await docClient.send(command); console.log(response); return response; };
  • 有关 API 的详细信息,请参阅 Amazon SDK for JavaScriptAPI 参考GetItem中的。

适用于 JavaScript (v2) 的软件开发工具包
注意

还有更多相关信息 GitHub。在 Amazon 代码示例存储库中查找完整示例,了解如何进行设置和运行。

从表中获取项目。

// Load the AWS SDK for Node.js var AWS = require("aws-sdk"); // Set the region AWS.config.update({ region: "REGION" }); // Create the DynamoDB service object var ddb = new AWS.DynamoDB({ apiVersion: "2012-08-10" }); var params = { TableName: "TABLE", Key: { KEY_NAME: { N: "001" }, }, ProjectionExpression: "ATTRIBUTE_NAME", }; // Call DynamoDB to read the item from the table ddb.getItem(params, function (err, data) { if (err) { console.log("Error", err); } else { console.log("Success", data.Item); } });

使用 DynamoDB 文档客户端从表中获取项目。

// Load the AWS SDK for Node.js var AWS = require("aws-sdk"); // Set the region AWS.config.update({ region: "REGION" }); // Create DynamoDB document client var docClient = new AWS.DynamoDB.DocumentClient({ apiVersion: "2012-08-10" }); var params = { TableName: "EPISODES_TABLE", Key: { KEY_NAME: VALUE }, }; docClient.get(params, function (err, data) { if (err) { console.log("Error", err); } else { console.log("Success", data.Item); } });
Kotlin
适用于 Kotlin 的 SDK
注意

还有更多相关信息 GitHub。在 Amazon 代码示例存储库中查找完整示例,了解如何进行设置和运行。

suspend fun getSpecificItem(tableNameVal: String, keyName: String, keyVal: String) { val keyToGet = mutableMapOf<String, AttributeValue>() keyToGet[keyName] = AttributeValue.S(keyVal) val request = GetItemRequest { key = keyToGet tableName = tableNameVal } DynamoDbClient { region = "us-east-1" }.use { ddb -> val returnedItem = ddb.getItem(request) val numbersMap = returnedItem.item numbersMap?.forEach { key1 -> println(key1.key) println(key1.value) } } }
  • 有关 API 的详细信息,请参阅适用GetItem于 K otlin 的 Amazon SDK API 参考

PHP
适用于 PHP 的 SDK
注意

还有更多相关信息 GitHub。在 Amazon 代码示例存储库中查找完整示例,了解如何进行设置和运行。

$movie = $service->getItemByKey($tableName, $key); echo "\nThe movie {$movie['Item']['title']['S']} was released in {$movie['Item']['year']['N']}.\n"; public function getItemByKey(string $tableName, array $key) { return $this->dynamoDbClient->getItem([ 'Key' => $key['Item'], 'TableName' => $tableName, ]); }
  • 有关 API 的详细信息,请参阅 Amazon SDK for PHPAPI 参考GetItem中的。

Python
SDK for Python(Boto3)
注意

还有更多相关信息 GitHub。在 Amazon 代码示例存储库中查找完整示例,了解如何进行设置和运行。

class Movies: """Encapsulates an Amazon DynamoDB table of movie data.""" def __init__(self, dyn_resource): """ :param dyn_resource: A Boto3 DynamoDB resource. """ self.dyn_resource = dyn_resource # The table variable is set during the scenario in the call to # 'exists' if the table exists. Otherwise, it is set by 'create_table'. self.table = None def get_movie(self, title, year): """ Gets movie data from the table for a specific movie. :param title: The title of the movie. :param year: The release year of the movie. :return: The data about the requested movie. """ try: response = self.table.get_item(Key={"year": year, "title": title}) except ClientError as err: logger.error( "Couldn't get movie %s from table %s. Here's why: %s: %s", title, self.table.name, err.response["Error"]["Code"], err.response["Error"]["Message"], ) raise else: return response["Item"]
  • 有关 API 的详细信息,请参阅适用GetItemPython 的 Amazon SDK (Boto3) API 参考

Ruby
适用于 Ruby 的 SDK
注意

还有更多相关信息 GitHub。在 Amazon 代码示例存储库中查找完整示例,了解如何进行设置和运行。

class DynamoDBBasics attr_reader :dynamo_resource attr_reader :table def initialize(table_name) client = Aws::DynamoDB::Client.new(region: "us-east-1") @dynamo_resource = Aws::DynamoDB::Resource.new(client: client) @table = @dynamo_resource.table(table_name) end # Gets movie data from the table for a specific movie. # # @param title [String] The title of the movie. # @param year [Integer] The release year of the movie. # @return [Hash] The data about the requested movie. def get_item(title, year) @table.get_item(key: {"year" => year, "title" => title}) rescue Aws::DynamoDB::Errors::ServiceError => e puts("Couldn't get movie #{title} (#{year}) from table #{@table.name}:\n") puts("\t#{e.code}: #{e.message}") raise end
  • 有关 API 的详细信息,请参阅 Amazon SDK for RubyAPI 参考GetItem中的。

SAP ABAP
SDK for SAP ABAP
注意

还有更多相关信息 GitHub。在 Amazon 代码示例存储库中查找完整示例,了解如何进行设置和运行。

TRY. oo_item = lo_dyn->getitem( iv_tablename = iv_table_name it_key = it_key ). DATA(lt_attr) = oo_item->get_item( ). DATA(lo_title) = lt_attr[ key = 'title' ]-value. DATA(lo_year) = lt_attr[ key = 'year' ]-value. DATA(lo_rating) = lt_attr[ key = 'rating' ]-value. MESSAGE 'Movie name is: ' && lo_title->get_s( ) && 'Movie year is: ' && lo_year->get_n( ) && 'Moving rating is: ' && lo_rating->get_n( ) TYPE 'I'. CATCH /aws1/cx_dynresourcenotfoundex. MESSAGE 'The table or index does not exist' TYPE 'E'. ENDTRY.
  • 有关 API 的详细信息,请参阅适用GetItem于 S AP 的 Amazon SDK ABAP API 参考

Swift
SDK for Swift
注意

这是预览版 SDK 的预发布文档。本文档随时可能更改。

注意

还有更多相关信息 GitHub。在 Amazon 代码示例存储库中查找完整示例,了解如何进行设置和运行。

/// Return a `Movie` record describing the specified movie from the Amazon /// DynamoDB table. /// /// - Parameters: /// - title: The movie's title (`String`). /// - year: The movie's release year (`Int`). /// /// - Throws: `MoviesError.ItemNotFound` if the movie isn't in the table. /// /// - Returns: A `Movie` record with the movie's details. func get(title: String, year: Int) async throws -> Movie { guard let client = self.ddbClient else { throw MoviesError.UninitializedClient } let input = GetItemInput( key: [ "year": .n(String(year)), "title": .s(title) ], tableName: self.tableName ) let output = try await client.getItem(input: input) guard let item = output.item else { throw MoviesError.ItemNotFound } let movie = try Movie(withItem: item) return movie }
  • 有关 API 的详细信息,请参阅适用于 S wift 的 Amazon SDK API 参考GetItem中。

有关更多 DynamoDB 示例,请参阅适用于使用 Amazon SDK 的 DynamoDB 的代码示例