DynamoDb Tutorial

This tutorial demonstrates using DynamoDB to read/write data from Amazon DynamoDB.

The example used in this tutorial is three end points:

POST /posts {"message":"Message to post"} to create a post
GET /posts/{id} to obtain a particular post
GET /posts to obtain all posts

REST endpoint configuration

The REST endpoints are configured as follows:

savePost:
  class: net.officefloor.tutorial.dynamodbhttpserver.DynamoDbLogic
  method: savePost

retrieveAllPosts:
  class: net.officefloor.tutorial.dynamodbhttpserver.DynamoDbLogic
  method: retrieveAllPosts

retrievePost:
  class: net.officefloor.tutorial.dynamodbhttpserver.DynamoDbLogic
  method: retrievePost

With the implementation as follows:

public class DynamoDbLogic {

	public void savePost(Post post, DynamoDBMapper dynamo) {
		dynamo.save(post);
	}

	public void retrievePost(@HttpPathParameter("id") String identifier, DynamoDBMapper dynamo,
			ObjectResponse<Post> response) {
		Post post = dynamo.load(Post.class, identifier);
		response.send(post);
	}

	public void retrieveAllPosts(DynamoDBMapper dynamo, ObjectResponse<Post[]> response) {
		PaginatedScanList<Post> page = dynamo.scan(Post.class, new DynamoDBScanExpression());
		response.send(page.toArray(new Post[1]));
	}
}

The DynamoDB entity is as follows:

@DynamoDBTable(tableName = "Post")
@HttpObject
@Data
@AllArgsConstructor
@NoArgsConstructor
public class Post {

	@DynamoDBHashKey
	@DynamoDBAutoGeneratedKey
	private String id;

	private String message;
}

Configuring DynamoDB

The following dependency is required:

		<dependency>
			<groupId>net.officefloor.persistence</groupId>
			<artifactId>officenosql_dynamodb</artifactId>
		</dependency>
		
		<!-- Required for testing -->
		<dependency>
			<groupId>net.officefloor.persistence</groupId>
			<artifactId>officenosql_dynamodb_test</artifactId>
			<scope>test</scope>
		</dependency>

DynamoDB is configured in officefloor/suppliers/DynamoDb.yml as follows:

source: net.officefloor.nosql.dynamodb.DynamoDbSupplierSource
properties:
  dynamo.entity.locators: net.officefloor.tutorial.dynamodbhttpserver.DynamoDbEntities

For performance reasons, the entities are not dynamically discovered. As Amazon Lambda starts instances as required, the application must be brought up quickly to service the first request. Having to inspect all jars and classes for entities is typically too slow. Therefore, DynamoDB requires registering all entities with it manually.

Therefore, to make the entities available to DynamoDB, the following is the above configured class:

public class DynamoDbEntities implements DynamoEntityLocator {

	@Override
	public Class<?>[] locateEntities() throws Exception {
		return new Class[] { Post.class };
	}

}

Note: for third party libraries requiring to store data, it is also possible to register entities via a DynamoEntityLocatorServiceFactory. This allows the entities to be automatically registered when the library is added to the class path.

Testing

To make local testing easier, the following unit tests demonstrate automatically setting up a local data store for testing.

	@Order(1)
	@RegisterExtension
	public final DynamoDbExtension dynamoDb = new DynamoDbExtension();

	@Order(2)
	@RegisterExtension
	public final MockWoofServerExtension server = new MockWoofServerExtension();

	@Test
	public void ensureCreatePost() throws Exception {

		// Have server create the post
		Post post = new Post(null, "TEST");
		MockWoofResponse response = this.server.send(MockWoofServer.mockJsonRequest(HttpMethod.POST, "/posts", post));
		response.assertResponse(204, "");

		// Ensure post created
		Post[] created = this.dynamoDb.getDynamoDbMapper().scan(Post.class, new DynamoDBScanExpression())
				.toArray(new Post[1]);
		assertEquals(1, created.length, "Should only be one created post");
		assertEquals("TEST", created[0].getMessage(), "Incorrect post");
	}

JUnit 4 example:

	private final DynamoDbRule dynamoDb = new DynamoDbRule();

	private final MockWoofServerRule server = new MockWoofServerRule();

	@Rule
	public final RuleChain ordered = RuleChain.outerRule(this.dynamoDb).around(this.server);

	@Test
	public void ensureCreatePost() throws Exception {

		// Have server create the post
		Post post = new Post(null, "TEST");
		MockWoofResponse response = this.server.send(MockWoofServer.mockJsonRequest(HttpMethod.POST, "/posts", post));
		response.assertResponse(204, "");

		// Ensure post created
		Post[] created = this.dynamoDb.getDynamoDbMapper().scan(Post.class, new DynamoDBScanExpression())
				.toArray(new Post[1]);
		assertEquals("Should only be one created post", 1, created.length);
		assertEquals("Incorrect post", "TEST", created[0].getMessage());
	}

The next tutorial covers AWS Serverless.