Reading a record

Written by

Yandex Cloud

Updated at January 30, 2024

To read a record from the Series table:

Java

Python

PHP

Node.js

Ruby

Create the SeriesItemOps02 project:
```
mvn -B archetype:generate \
  -DarchetypeGroupId=org.apache.maven.archetypes \
  -DgroupId=com.mycompany.app \
  -DartifactId=SeriesItemOps02
```
As a result of running the command, the SeriesItemOps02 project folder is created in the current working folder with a structure of subfolders and the pom.xml project description file.
Go to the project folder:
```
cd SeriesItemOps02
```

Edit the project description in the pom.xml file, for example, using the nano editor:

nano pom.xml

Sample pom.xml file:

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <groupId>com.mycompany.app</groupId>
  <artifactId>SeriesItemOps02</artifactId>
  <packaging>jar</packaging>
  <version>1.0-SNAPSHOT</version>
  <name>SeriesItemOps02</name>
  <url>http://maven.apache.org</url>
  <build>
      <plugins>
          <plugin>
              <groupId>org.apache.maven.plugins</groupId>
              <artifactId>maven-jar-plugin</artifactId>
              <configuration>
                  <archive>
                      <manifest>
                          <addClasspath>true</addClasspath>
                          <classpathPrefix>lib/</classpathPrefix>
                          <mainClass>com.mycompany.app.SeriesItemOps02</mainClass>
                      </manifest>
                      <manifestEntries>
                          <Class-Path>.</Class-Path>
                      </manifestEntries>
                  </archive>
                  <finalName>release/SeriesItemOps02</finalName>
              </configuration>
          </plugin>
          <plugin>
              <groupId>org.apache.maven.plugins</groupId>
              <artifactId>maven-dependency-plugin</artifactId>
              <executions>
                  <execution>
                      <id>copy-dependencies</id>
                      <phase>prepare-package</phase>
                      <goals>
                          <goal>copy-dependencies</goal>
                      </goals>
                      <configuration>
                          <outputDirectory>${project.build.directory}/release/lib</outputDirectory>
                          <overWriteReleases>false</overWriteReleases>
                          <overWriteSnapshots>false</overWriteSnapshots>
                          <overWriteIfNewer>true</overWriteIfNewer>
                      </configuration>
                  </execution>
              </executions>
          </plugin>
      </plugins>
  </build>
  <dependencies>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>4.13.1</version>
      <scope>test</scope>
    </dependency>
    <dependency>
      <groupId>com.amazonaws</groupId>
      <artifactId>aws-java-sdk-dynamodb</artifactId>
      <version>1.11.1012</version>
    </dependency>
  </dependencies>
  <properties>
    <maven.compiler.source>1.8</maven.compiler.source>
    <maven.compiler.target>1.8</maven.compiler.target>
  </properties>
</project>

Check the current versions of junit and aws-java-sdk-dynamodb.

In the folder src/main/java/com/mycompany/app/, create the SeriesItemOps02.java file, for example, using the nano editor:

nano src/main/java/com/mycompany/app/SeriesItemOps02.java

Copy the following code to the created file:

Warning

Instead of <Document_API_endpoint>, specify the prepared value.

package com.mycompany.app;

import com.amazonaws.client.builder.AwsClientBuilder;
import com.amazonaws.services.dynamodbv2.AmazonDynamoDB;
import com.amazonaws.services.dynamodbv2.AmazonDynamoDBClientBuilder;
import com.amazonaws.services.dynamodbv2.document.DynamoDB;
import com.amazonaws.services.dynamodbv2.document.Item;
import com.amazonaws.services.dynamodbv2.document.Table;
import com.amazonaws.services.dynamodbv2.document.spec.GetItemSpec;

public class SeriesItemOps02 {

    public static void main(String[] args) throws Exception {

        AmazonDynamoDB client = AmazonDynamoDBClientBuilder.standard()
            .withEndpointConfiguration(new AwsClientBuilder.EndpointConfiguration("<Document_API_endpoint>", "ru-central1"))
            .build();

        DynamoDB dynamoDB = new DynamoDB(client);

        Table table = dynamoDB.getTable("Series");

        int series_id = 3;
        String title = "Supernatural";

        GetItemSpec spec = new GetItemSpec().withPrimaryKey("series_id", series_id, "title", title);

        try {
            System.out.println("Trying to retrieve a record...");
            Item outcome = table.getItem(spec);
            System.out.println("Record retrieved: " + outcome);
        }
        catch (Exception e) {
            System.err.println("Couldn't retrieve record: " + series_id + " " + title);
            System.err.println(e.getMessage());
        }

    }
}

To read a record by its primary key, the getItem method is used.

Build a project:
```
mvn package
```
As a result of running the command, the SeriesItemOps02.jar file is generated in the folder target/release/.

Run the application:

java -jar target/release/SeriesItemOps02.jar

Result:

Attempting to obtain record...
Record obtained: { Item: {title=Supernatural, series_id=3, info={release_date=2015-09-13, series_info=Supernatural is an American television series created by Eric Kripke}} }

Create the SeriesItemOps02.py file, for example, using the nano editor:

nano SeriesItemOps02.py

Copy the following code to the created file:

Warning

Instead of <Document_API_endpoint>, specify the prepared value.

from pprint import pprint
import boto3
from botocore.exceptions import ClientError

def get_serie(title, series_id):
    ydb_docapi_client = boto3.resource('dynamodb', endpoint_url = "<Document_API_endpoint>")

    table = ydb_docapi_client.Table('Series')

    try:
        response = table.get_item(Key = {'series_id': series_id, 'title': title})
    except ClientError as e:
        print(e.response['Error']['Message'])
    else:
        return response['Item']

if __name__ == '__main__':
    serie = get_serie("Supernatural", 3,)
    if serie:
        print("Record retrieved:")
        pprint(serie, sort_dicts = False)

To read a record from the table, use the get_item method that passes the primary key of the desired item.

Run the program:

python SeriesItemOps02.py

Result:

Record retrieved:
{'series_id': Decimal('3'),
'title': ' Supernatural,
'info': {'release_date': 2015-09-13',
          'series_info': 'Supernatural is an American television series '
                        'created by Eric Kripke'}}

Create the SeriesItemOps02.php file, for example, using the nano editor:

nano SeriesItemOps02.php

Copy the following code to the created file:

Warning

Instead of <Document_API_endpoint>, specify the prepared value.

<?php

require 'vendor/autoload.php';

date_default_timezone_set('UTC');

use Aws\DynamoDb\Exception\DynamoDbException;
use Aws\DynamoDb\Marshaler;

$sdk = new Aws\Sdk([
    'endpoint' => '<Document_API_endpoint>',
    'region'   => 'ru-central1',
    'version'  => 'latest'
]);

$dynamodb = $sdk->createDynamoDb();
$marshaler = new Marshaler();

$tableName = 'Series';

$series_id = 3;
$title = 'Supernatural';

$key = $marshaler->marshalJson('
    {
        "series_id": ' . $series_id . ',
        "title": "' . $title . '"
    }
');

$params = [
    'TableName' => $tableName,
    'Key' => $key
];

try {
    $result = $dynamodb->getItem($params);
    echo json_encode($result["Item"], JSON_PRETTY_PRINT);

} catch (DynamoDbException $e) {
    echo "Couldn't retrieve record:\n";
    echo $e->getMessage() . "\n";
}

?>

To read a record by its primary key, the getItem method is used.

Run the program:

php SeriesItemOps02.php

Result:

{
    "series_id": {
        "N": ".3e1"
    },
    "title": {
        "S": "Supernatural"
    },
    "info": {
        "M": {
            "release_date": {
                "S": "2015-09-13"
            },
            "series_info": {
                "S": "Supernatural is an American television series created by Eric Kripke"
            }
        }
    }
}

Create the SeriesItemOps02.js file, for example, using the nano editor:

nano SeriesItemOps02.js

Copy the following code to the created file:

Warning

Instead of <Document_API_endpoint>, specify the prepared value.

const AWS = require("@aws-sdk/client-dynamodb");
const { marshall } = require("@aws-sdk/util-dynamodb");

// Credentials should be defined via environment variables AWS_SECRET_ACCESS_KEY and AWS_ACCESS_KEY_ID
const dynamodb = new AWS.DynamoDBClient({
    region: "ru-central1",
    endpoint: "<Document_API_endpoint>",
});

const table = "Series";
const series_id = 3;
const title = "Supernatural";

dynamodb.send(new AWS.GetItemCommand({
    TableName: table,
    Key: marshall({
        "series_id": series_id,
        "title": title
    })
}))
    .then(data => {
        console.log("Record read successfully:", JSON.stringify(data, null, 2));
    })
    .catch(err => {
        console.error("Couldn't read record. JSON error:", JSON.stringify(err, null, 2));
    })

To read a record from the table, use the command GetItemCommand. By specifying the primary key values (series_id and title), you can read any record from the Series table.

Run the program:

node SeriesItemOps02.js

Result:

Record read: {
  "Item": {
    "series_id": 3,
    "title": "Supernatural",
    "info": {
      "series_info": "Supernatural is an American television series created by Eric Kripke",
      "release_date": "2015-09-13"
    }
  }
}

Create the SeriesItemOps02.rb file, for example, using the nano editor:

nano SeriesItemOps02.rb

Copy the following code to the created file:

Warning

Instead of <Document_API_endpoint>, specify the prepared value.

require 'aws-sdk-dynamodb'

def get_item_from_table(dynamodb_client, table_item)
  result = dynamodb_client.get_item(table_item)
  puts "#{result.item['title']} (#{result.item['series_id'].to_i}):"
  puts "  Release date: #{result.item['info']['release_date']}"
  puts "  Series info: #{result.item['info']['series_info']}"
rescue StandardError => e
  puts "Error retrieving series '#{table_item[:key][:title]} " \
        "(#{table_item[:key][:series_id]})': #{e.message}"
end

def run_me
  region = 'ru-central1'
  table_name = 'Series'
  title = 'Supernatural'
  series_id = 3

  Aws.config.update(
    endpoint: '<Document_API_endpoint>',
    region: region
  )

  dynamodb_client = Aws::DynamoDB::Client.new

  table_item = {
    table_name: table_name,
    key: {
      series_id: series_id,
      title: title
    }
  }

  puts "Retrieving data about '#{title} (#{series_id})' " \
    "from the table '#{table_name}'..."
  get_item_from_table(dynamodb_client, table_item)
end

run_me if $PROGRAM_NAME == __FILE__

To read a record from a table, use the get_item method, in which you can specify the primary key value (series_id and title) to read any record from the Series table.

Run the program:

ruby SeriesItemOps02.rb

Result:

Getting information about 'Supernatural (3)' from table 'Series'...
Supernatural (3):
  Release date: 2015-09-13
  Series info: Supernatural is an American television series created by Eric Kripke

Reading a record

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