Verifying the attribute in DynamoDB without using scan? - amazon-dynamodb

Question

How to verify an attribute whether it present in table or not without using scan in dynamodb?
In my usecase, From client side, The customer request with their Customer_id for knowing the values of the product. In server side, have to check whether the entered customer_id already present in DynamoDB table or not. If not, have to make a new entry.
How can I implement this case without using SCAN operation to the table?

Answer 1

It sounds to me that you want to do a conditional PutItem on this table: put the item into the table if there is not another item with the same customer_id. This is easy enough to do because the customer_id is the hash key of the table. From the PutItem documentation:
Note
To prevent a new item from replacing an existing item, use a conditional put operation with ComparisonOperator set to NULL for the
primary key attribute, or attributes.
Here is a quick example I coded up using the Dynamo DB document API in the Java SDK and running against DynamoDB Local:
import com.amazonaws.auth.BasicAWSCredentials;
import com.amazonaws.services.dynamodbv2.AmazonDynamoDB;
import com.amazonaws.services.dynamodbv2.AmazonDynamoDBClient;
import com.amazonaws.services.dynamodbv2.document.DynamoDB;
import com.amazonaws.services.dynamodbv2.document.Expected;
import com.amazonaws.services.dynamodbv2.document.Item;
import com.amazonaws.services.dynamodbv2.document.Table;
import com.amazonaws.services.dynamodbv2.model.AttributeDefinition;
import com.amazonaws.services.dynamodbv2.model.ConditionalCheckFailedException;
import com.amazonaws.services.dynamodbv2.model.CreateTableRequest;
import com.amazonaws.services.dynamodbv2.model.KeySchemaElement;
import com.amazonaws.services.dynamodbv2.model.KeyType;
import com.amazonaws.services.dynamodbv2.model.ProvisionedThroughput;
import com.amazonaws.services.dynamodbv2.model.ScalarAttributeType;
import com.amazonaws.services.dynamodbv2.util.Tables;
public class StackOverflow {
private static final String EXAMPLE_TABLE_NAME = "example_table";
public static void main(String[] args) {
AmazonDynamoDB client = new AmazonDynamoDBClient(new BasicAWSCredentials("accessKey", "secretKey"));
client.setEndpoint("http://localhost:4000");
DynamoDB dynamoDB = new DynamoDB(client);
if (Tables.doesTableExist(client, "example_table")) client.deleteTable(EXAMPLE_TABLE_NAME);
// Create table with hash key 'customer_id'
CreateTableRequest createTableRequest = new CreateTableRequest();
createTableRequest.withTableName(EXAMPLE_TABLE_NAME);
createTableRequest.withKeySchema(new KeySchemaElement("customer_id", KeyType.HASH));
createTableRequest.withAttributeDefinitions(new AttributeDefinition("customer_id", ScalarAttributeType.S));
createTableRequest.withProvisionedThroughput(new ProvisionedThroughput(15l, 15l));
dynamoDB.createTable(createTableRequest);
Tables.waitForTableToBecomeActive(client, EXAMPLE_TABLE_NAME);
Table exampleTable = dynamoDB.getTable(EXAMPLE_TABLE_NAME);
exampleTable.putItem(new Item()
.withPrimaryKey("customer_id", "ABCD")
.withString("customer_name", "Jim")
.withString("customer_email", "jim#gmail.com"));
System.out.println("After Jim:");
exampleTable.scan()
.forEach(System.out::println);
System.out.println();
try {
exampleTable.putItem(new Item()
.withPrimaryKey("customer_id", "EFGH")
.withString("customer_name", "Garret")
.withString("customer_email", "garret#gmail.com"), new Expected("customer_id").notExist());
} catch (ConditionalCheckFailedException e) {
System.out.println("Conditional check failed!");
}
System.out.println("After Garret:");
exampleTable.scan()
.forEach(System.out::println);
System.out.println();
try {
exampleTable.putItem(new Item()
.withPrimaryKey("customer_id", "ABCD")
.withString("customer_name", "Bob")
.withString("customer_email", "bob#gmail.com"), new Expected("customer_id").notExist());
} catch (ConditionalCheckFailedException e) {
System.out.println("Conditional check failed!");
}
System.out.println("After Bob:");
exampleTable.scan()
.forEach(System.out::println);
}
}
Output:
After Jim:
{ Item: {customer_email=jim#gmail.com, customer_name=Jim, customer_id=ABCD} }
After Garret:
{ Item: {customer_email=garret#gmail.com, customer_name=Garret, customer_id=EFGH} }
{ Item: {customer_email=jim#gmail.com, customer_name=Jim, customer_id=ABCD} }
Conditional check failed!
After Bob:
{ Item: {customer_email=garret#gmail.com, customer_name=Garret, customer_id=EFGH} }
{ Item: {customer_email=jim#gmail.com, customer_name=Jim, customer_id=ABCD} }