Getting started with Amazon DynamoDB

0) Sign up for an Amazon AWS account

Go to www.aws.amazon.com and signup for a free AWS account. With a free account you can obtain DynamoDB with up to 5 reads / sec and 5 writes / sec.

1) Install AWS sdk for php

Assuming you have pear already installed in your system enter the following commands (for more information on pear, see http://pear.php.net/):

 pear channel-discover pear.amazonwebservices.com pear install aws/sdk 

Now some configuration files need to be modified in order to connect to your DynamoDB:

Go to your AWS management console (www.console.aws.amazon.com), click on your user name (top-right corner) and select “Security credentials”. Here you’ll find your Access Key Id and your Secret Access Key. Insert these credentials in the following file:

 ~/pear/share/pear/AWSSDKforPHP/sample-config.inc.php 

and save the file with the name “config.inc.php”

 sudo mv ~/pear/share/pear/AWSSDKforPHP/sample-config.inc.php ~/pear/share/pear/AWSSDKforPHP/config.inc.php 

Once the sdk is installed and configured, you can use its APIs by including it with the following command: 

 require_once 'AWSSDKforPHP/sdk.class.php'; 

 and establish a connection with your DynamoDB with: 

 $dynamodb = new AmazonDynamoDB(); 

2) Install AWS Toolkit for Eclipse/Aptana

With the AWS Toolkit for Eclipse/Aptana, it’s possible to manage your DynamoDB tables without having to login to the AWS management console.

To install it, follow the next steps:

• Start Eclipse/Aptana
• Open Help -> Install New Software….
• Enter http://aws.amazon.com/eclipse in the text box labeled “Work with” at the top of the dialog.
• Select “AWS Toolkit for Eclipse” from the list below.
• Click “Next”. Eclipse/Aptana guides you through the remaining installation steps.
• Restart Eclipse/Aptana;
• Go to preferences -> AWS Toolkit and insert your account’s credentials*.

3) Start using DynamoDB

Below I provide some instructions to start using DynamoDB through the AWS SDK. Starting from creating a new table, loading data into it and perform a simple query.

3.1) Create Table

To create a table, go to the AWS explorer in Eclipse/Aptana, right click on Amazon DynamoDB and click on “Create Table”. Define the Table name, the key attribute and value and define (if needed) the range key attribute and value. This last parameter represents a secondary key to filter data.

Let’s assume that you want to create a table called “Websites” that has two columns: id (key)(String) and URL (String) 

3.2) Load data

To insert one row in your new table use the following function:

 $dynamodb = new AmazonDynamoDB(); $generatedId = uniqid(); $websiteUrl = ‘http://www.grio.com’; $put_response = $dynamodb->put_item(array( 'TableName' => “Websites”, 'Item' => array( 'id' => array( AmazonDynamoDB::TYPE_STRING => $generatedId ), 'URL' => array( AmazonDynamoDB::TYPE_STRING => $websiteUrl ) ) )); 

3.3) Query data

To query DynamoDB two methods can be used. The first one is called “query” and helps you to find the row identified by the provided key.

 $dynamodb = new AmazonDynamoDB(); $grioId = “4f605c68e8c14” $response = $dynamodb->query(array( 'TableName' => “Websites”, 'HashKeyValue' => array( AmazonDynamoDB::TYPE_STRING => $grioId ), )); 

This will return the URL corresponding to the generated unique id (key) in the table “Webistes”.

The second method for querying DynamoDB is called “scan” and allows you to get the all table and filter it using more than one field.

 $dynamodb = new AmazonDynamoDB(); $scan_response = $dynamodb->scan(array('TableName' => 'ProductCatalog', 'AttributesToGet' => array('Id'), 'ScanFilter' => array('Price' => array( 'ComparisonOperator' => AmazonDynamoDB::CONDITION_LESS_THAN, 'AttributeValueList' => array( array( AmazonDynamoDB::TYPE_NUMBER => '100' )) )) )); 

Suppose you have a table called ProductCatalog that contains the ids and the prices of all the products.

The response of the above request will contain all the ids of Products with a Price lower than 100$.

“Scan” allows you to perform “more complex” queries but “query” guarantees better performances.

3.4) Parse response

The results of the above queries will be an Object of the type ECFResponse whose most important part is the body (that is a CFSimpleXML Object). To access the number of rows returned by the query it’s sufficient to look at the Count attribute:

 $response->body->Count; 

To get a specific field (e.g. URL) of the n^th element of the response it’s necessary to access the Items attribute in the following way:

 (string) $response->body->Items[n]->URL->S; 

Where the cast ( “(string)” ) and the last letter “S”, depend on the type of the field ( in this case URL it’s an AmazonDynamoDB::TYPE_STRING as specified in 3.2).

Now you have all you need to start using DynamoDB for your application.

Summarizing, Amazon DynamoDB is a useful service if you need a simple, plug-and-play, scalable db. It becomes less handy if scalability is not your first concern or if your application needs to perform very complex queries. This said, we’re still talking of a very new product, which is going to improve over time.

To learn more about DynamoDB’s characteristics and APIs, go to its official website http://aws.amazon.com/dynamodb/ and reading its documentation at http://docs.amazonwebservices.com/amazondynamodb/

Alberto Montagnese