Month: August 2016

Update DynamoDB Items with Node.js

On a previous post we proceeded into inserting items to DynamoDB using Node.js. 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.

var updateName = function(email,fullName,callback) {
	
	var docClient = new AWS.DynamoDB.DocumentClient();
	
	var params = {
			TableName:"Users",
			Key: {
				email : email
			},
			UpdateExpression: "set fullname = :fullname",
		    ExpressionAttributeValues:{
		        ":fullname":fullName
		    },
		    ReturnValues:"UPDATED_NEW"
		};
	
	docClient.update(params,callback);
}

We can proceed on more advanced statements using conditional updates. Conditional updates can help us in many cases such as handling concurrent updates. In our case we will update an item’s Full name only if it starts with a certain prefix.

var updateConditionally = function(email,fullName,prefix,callback) {
	
	var docClient = new AWS.DynamoDB.DocumentClient();
	
	var params = {
			TableName:"Users",
			Key: {
				email : email
			},
			UpdateExpression: "set fullname = :fullname",
			ConditionExpression: "begins_with(fullname,:prefix)",
			ExpressionAttributeValues:{
		        ":fullname":fullName,
		        ":prefix":prefix
		    },
		    ReturnValues:"UPDATED_NEW"
		};
	
	docClient.update(params,callback);
}

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.

var addUpdateCounter = function(email,callback) {
	
	var docClient = new AWS.DynamoDB.DocumentClient();
	
	var params = {
			TableName:"Users",
			Key: {
				email : email
			},
			UpdateExpression: "set #counter = :counter",
			ExpressionAttributeNames:{
		        "#counter":"counter"
		    },
			ExpressionAttributeValues:{
		        ":counter":0
		    },
			ReturnValues:"UPDATED_NEW"
		};
	
	docClient.update(params,callback);
}

var updateAndIncreaseCounter = function(email,fullName,callback) {

	var docClient = new AWS.DynamoDB.DocumentClient();
	
	var params = {
			TableName:"Users",
			Key: {
				email : email
			},
			UpdateExpression: "set fullname = :fullname ADD #counter :incva",
			ExpressionAttributeNames:{
		        "#counter":"counter"
		    },
			ExpressionAttributeValues:{
		        ":fullname":fullName,
		        ":incva":1
		    },
		    ReturnValues:"UPDATED_NEW"
		};
	
	docClient.update(params,callback);
}

You can find the sourcecode on github.

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Update DynamoDB Items with Java

On a previous post we proceeded into 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 more advanced statements using conditional updates. Conditional updates can help us in many cases such as handling concurrent updates.

We can achieve so 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 through 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);
    }

You can find the sourcecode on github.