In a previous post, we showed inserting items to DynamoDB using Java. DynamoDB also supports updating items.

We will use the Login table for the update examples. When issuing an update you must specify the primary key of the item you want to update.

public void updateName(String email,String fullName) {

    Map<String,AttributeValue> attributeValues = new HashMap<>();
    attributeValues.put("email",new AttributeValue().withS(email));
    attributeValues.put("fullname",new AttributeValue().withS(fullName));

    UpdateItemRequest updateItemRequest = new UpdateItemRequest()
        .withTableName(TABLE_NAME)
        .addKeyEntry("email",new AttributeValue().withS(email))
        .addAttributeUpdatesEntry("fullname",
            new AttributeValueUpdate().withValue(new AttributeValue().withS(fullName)));

    UpdateItemResult updateItemResult = amazonDynamoDB.updateItem(updateItemRequest);
}

We can proceed on to more advanced statements using conditional updates. Conditional updates can help us in many cases, such as handling concurrent updates.

We can achieve this by using plain expressions.

public void updateConditionallyWithExpression(String email,String fullName,String prefix) {

    Map<String, AttributeValue> key = new HashMap<>();
    key.put("email", new AttributeValue().withS(email));

    Map<String, AttributeValue> attributeValues = new HashMap<>();
    attributeValues.put(":prefix", new AttributeValue().withS(prefix));
    attributeValues.put(":fullname", new AttributeValue().withS(fullName));

    UpdateItemRequest updateItemRequest = new UpdateItemRequest()
        .withTableName(TABLE_NAME)
        .withKey(key)
        .withUpdateExpression("set fullname = :fullname")
        .withConditionExpression("begins_with(fullname,:prefix)")
        .withExpressionAttributeValues(attributeValues);
    UpdateItemResult updateItemResult = amazonDynamoDB.updateItem(updateItemRequest);
}

Or by specifying attributes.

public void updateConditionallyWithAttributeEntries(String email, String fullName, String prefix){

    Map<String,AttributeValue> key = new HashMap<>();
    key.put("email",new AttributeValue().withS(email));

    UpdateItemRequest updateItemRequest = new UpdateItemRequest()
        .withTableName(TABLE_NAME)
        .withKey(key)
        .addAttributeUpdatesEntry("fullname",new AttributeValueUpdate().withValue(new AttributeValue().withS(fullName)).withAction(AttributeAction.PUT))
        .addExpectedEntry("fullname",new ExpectedAttributeValue().withValue(new AttributeValue().withS(prefix)).withComparisonOperator(ComparisonOperator.BEGINS_WITH));

    UpdateItemResult updateItemResult = amazonDynamoDB.updateItem(updateItemRequest);
}

Another feature is atomic counters. We can issue updates to a DynamoDB item and increase the attribute values. We will add an extra field called count. Also, we will add another update function, which once called will update the field specified but will also increase the counter attribute. Thus, the counter attribute will represent how many times an update was performed on a specific item.

public void addUpdateCounter(String email) {

    Map<String,AttributeValue> key = new HashMap<>();
    key.put("email",new AttributeValue().withS(email));

    UpdateItemRequest updateItemRequest = new UpdateItemRequest()
        .withTableName(TABLE_NAME)
        .withKey(key)
        .addAttributeUpdatesEntry("counter",new AttributeValueUpdate().withValue(new AttributeValue().withN("0")).withAction(AttributeAction.PUT));

   UpdateItemResult updateItemResult = amazonDynamoDB.updateItem(updateItemRequest);
}

public void updateAndIncreaseCounter(String email,String fullname) {

    Map<String,AttributeValue> key = new HashMap<>();
    key.put("email",new AttributeValue().withS(email));

    UpdateItemRequest updateItemRequest = new UpdateItemRequest()
        .withTableName(TABLE_NAME)
        .withKey(key)
        .addAttributeUpdatesEntry("fullname",new AttributeValueUpdate().withValue(new AttributeValue().withS(fullname)).withAction(AttributeAction.PUT))
        .addAttributeUpdatesEntry("counter",new AttributeValueUpdate().withValue(new AttributeValue().withN("1")).withAction(AttributeAction.ADD));

    UpdateItemResult updateItemResult = amazonDynamoDB.updateItem(updateItemRequest);
}

And that's that. As usual, you can find the source code on GitHub.