Object persistence (high-level) interface

In the object persistence interface, you will not perform any CRUD operations directly on the data; instead, you have to create objects which represent DynamoDB tables and indexes and perform operations on those objects. It will allow you to write object-centric code and not database-centric code.

Let's create a DynamoDBMapper object in AWS SDK for Java. It will represent data in the Movies table. This is the MovieObjectMapper.java class. Here you can use the Eclipse IDE for the example.

You need to import a few classes for annotations. DynamoDBAttribute is applied to the getter method. If it will apply to the class field then its getter and setter method must be declared in the same class. The DynamoDBHashKey annotation marks property as the hash key for the modeled class. The DynamoDBTable annotation marks DynamoDB as the table name:

@DynamoDBTable(tableName="Movies")

It specifies the table name:

@DynamoDBHashKey(attributeName="name")
public String getName() { return name;}
public void setName(String name) {this.name = name;}

@DynamoDBAttribute(attributeName = "year")
public int getYear() { return year; }
public void setYear(int year) { this.year = year; }

In the preceding code, DynamoDBHashKey has been defined as the hash key for the name attribute and its getter and setter methods. DynamoDBAttribute specifies the column name and its getter and setter methods.

Now create MovieObjectPersistenceExample.java to retrieve the movie year:

static AmazonDynamoDB client;

The preceding code will create the client instance. You have to assign the credentials and region to this instance. You need to import DynamoDBMapper, which will be used to fetch the year from the Movies table:

DynamoDBMapper mapper = new DynamoDBMapper(client);
MovieObjectMapper movieObjectMapper = new MovieObjectMapper();
movieObjectMapper.setName("Airplane");

The mapper object will be created from DynamoDBMapper by passing the client.

The movieObjectMapper object will be created from the POJO class, which we created earlier. In this object, set the movie name as the parameter:

MovieObjectMapper result = mapper.load(movieObjectMapper);
if (result != null) {
System.out.println("The song was released in "+ result.getYear());
}

Create the result object by calling DynamoDBMapper object's load method. If the result is not null then it will print the year from the result's getYear() method.