DynamoDB Series Kickoff

Last week, Amazon DynamoDB added support for JSON document data structures. With this update, DynamoDB now supports nested data in the form of lists (L type) and maps (M type). Also part of this update was native support for booleans (BOOL type) and nulls (NULL type).

This week, we will be running a series of daily blog posts that will explain the new changes and how they relate to the AWS SDK for .NET, and we will see how you can take advantage of these new types to work with complex objects in all three .NET SDK DynamoDB APIs. In this, the first blog post of series, we will see how the low-level API has changed. In the following days, we will cover the Document Model, Conversion Schemas, Object Persistence Model, and finally Expressions.

New types

Until now, DynamoDB had only six data types:

• Scalars N, S, and B that represent number, string, and binary data.
• Sets NS, SS, and BS that represent number set, string set, and binary set.
  Sets have the limitation that the data they store has to be homogeneous (e.g., SS could only contain S elements) and unique (no two elements could be the same).

This release expands the possible data types with four new additions:

• BOOL represents boolean data.
• NULL represents null values.
• L type represents a list of elements.
• M type represents a string-to-element map.

The key point about L and M types is that they can contain any DynamoDB type. This allows you to create, for example, lists of maps of lists, which in turn can contain a mix of numbers, strings, bools, and nulls, or any other conceivable combination of attributes.

Low-level

The low-level API changes are straightforward: new DynamoDB types are now supported in all data calls. Here’s a sample that shows how both old and new types can be used in a PutItem call.

// Put item
client.PutItem("SampleTable", new Dictionary<string, AttributeValue>
{
    { "Id", new AttributeValue { N = "1" } },
    { "Product", new AttributeValue { S = "DataWriter" } },
    { "Aliases", new AttributeValue {
        SS = new List<string> { "Prod", "1.0" } } },
    { "IsPublic", new AttributeValue { BOOL = false } },
    { "Metadata", new AttributeValue {
        M = new Dictionary<string, AttributeValue>
        {
            { "InternalVersion", new AttributeValue { N = "1.2" } },
            { "Developers", new AttributeValue {
                SS = new List<string> { "Alan", "Franko" } } 
            },
            { "SampleInput", new AttributeValue {
                L = new List<AttributeValue>
                {
                    new AttributeValue { BOOL = true },
                    new AttributeValue { N =  "42" },
                    new AttributeValue { NULL = true },
                    new AttributeValue {
                        SS = new List<string> { "apple", "orange" } }
                } }
            }
        } }
    }
});

As you can see, the new M and L AttributeValue types may contain AttributeValues, allowing complex, nested data to be stored in a single DynamoDB record. In the above example, the item we just stored into DynamoDB will have an attribute of type M named “Metadata”. This attribute will in turn contain three other attributes: N (number), SS (string set), and L (list). The list contains four more attributes, which in turn can be other M and L types, though in our example they are not.

Tomorrow, we will take a look at how the new additions can be used with the Document Model API.