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AWS Mobile SDK
Xamarin Developer Guide

Using the Object Persistence Model

The AWS Mobile SDK for .NET and Xamarin provides an Object Persistence model that enables you to map your client-side classes to a DynamoDB table. Each object instance then maps to an item in the corresponding table. To save your client-side objects to a table, the Object Persistence model provides the DynamoDBContext class, an entry point to DynamoDB. This class provides you a connection to DynamoDB and enables you to access tables, perform various CRUD operations, and execute queries.

The Object Persistence model does not provide an API to create, update, or delete tables. It provides only data operations. To create, update and delete tables, you must use the low-level API. For instructions on how to use the low-level API, see Using the DynamoDB Service Level APIs.

Overview

The Object Persistence model provides a set of attributes to map client-side classes to tables, and properties/fields to table attributes. The Object Persistence model supports both the explicit and default mapping between class properties and table attributes.

  • Explicit mapping: To map a property to a primary key, you must use the DynamoDBHashKey and DynamoDBRangeKey Object Persistence model attributes. Additionally, for the non-primary key attributes, if a property name in your class and the corresponding table attribute to which you want to map it are not the same, then you must define the mapping by explicitly adding the DynamoDBProperty attribute.

  • Default mapping - By default, the Object Persistence model maps the class properties to the attributes with the same name in the table.

You do not have to map every single class property. You identify these properties by adding the DynamoDBIgnore attribute. Saving and retrieving an instance of an object would omit any property marked with this attribute.

Supported Data Types

The Object Persistence model supports a set of primitive .NET data types, collections, and arbitrary data types. The model supports the following primitive data types.

  • bool

  • byte

  • char

  • DateTime

  • decimal, double, float

  • Int16, Int32, Int64

  • SByte

  • string

  • UInt16, UInt32, UInt64

The Object Persistence model also supports the .NET collection types with the following limitations:

  • Collection type must implement ICollection interface.

  • Collection type must be composed of the supported primitive types. For example, ICollection<string>, ICollection<bool>.

  • Collection type must provide a parameter-less constructor.

For more information on the Object Persistence model, see .NET Object Persistence Model.

Create a DynamoDB Client

To create a DynamoDB client:

var client = new AmazonDynamoDBClient(credentials,region); DynamoDBContext context = new DynamoDBContext(client);

CRUD Operations

Save an Object

Create an object:

[DynamoDBTable("Books")] public class Book { [DynamoDBHashKey] // Hash key. public string Id { get; set; } [DynamoDBGlobalSecondaryIndexHashKey] public string Author { get; set; } [DynamoDBGlobalSecondaryIndexRangeKey] public string Title { get; set; } public string ISBN { get; set; } public int Price { get; set; } public string PageCount { get; set; } } Book myBook = new Book { Id = id, Author = "Charles Dickens", Title = "Oliver Twist", ISBN = "111-1111111001", Price = 10, PageCount = 300 };

Save an object to a DynamoDB table:

context.Save(myBook);

Retrieve an Object

To retrieve an object:

Book retrievedBook = context.Load<Book>(1);

Update an Object

To update an object:

Book retrievedBook = context.Load<Book>(1); retrievedBook.ISBN = "111-1111111001"; context.Save(retrievedBook);

Delete an Object

To delete an object:

Book retrievedBook = context.Load<Book>(1); context.Delete(retrievedBook);

Query and Scan

To query and retrieve all books whose author is "Charles Dickens":

public async Task QueryAsync(AWSCredentials credentials, RegionEndpoint region) { var client = new AmazonDynamoDBClient(credentials, region); DynamoDBContext context = new DynamoDBContext(client); var search = context.FromQueryAsync < Book > (new Amazon.DynamoDBv2.DocumentModel.QueryOperationConfig() { IndexName = "Author-Title-index", Filter = new Amazon.DynamoDBv2.DocumentModel.QueryFilter("Author", Amazon.DynamoDBv2.DocumentModel.QueryOperator.Equal, "Charles Dickens") }); Console.WriteLine("items retrieved"); var searchResponse = await search.GetRemainingAsync(); searchResponse.ForEach((s) = > { Console.WriteLine(s.ToString()); }); }

The scan example code below returns all books in our table:

public async Task ScanAsync(AWSCredentials credentials, RegionEndpoint region) { var client = new AmazonDynamoDBClient(credentials, region); DynamoDBContext context = new DynamoDBContext(client); var search = context.FromScanAsync < Book > (new Amazon.DynamoDBv2.DocumentModel.ScanOperationConfig() { ConsistentRead = true }); Console.WriteLine("items retrieved"); var searchResponse = await search.GetRemainingAsync(); searchResponse.ForEach((s) = > { Console.WriteLine(s.ToString()); }); }