Working with Items in DynamoDB Using the AWS SDK for .NET Document Model - Amazon DynamoDB

Working with Items in DynamoDB Using the AWS SDK for .NET Document Model

To perform data operations using the document model, you must first call the Table.LoadTable method, which creates an instance of the Table class that represents a specific table. The following C# example creates a Table object that represents the ProductCatalog table in Amazon DynamoDB.

Example

Table table = Table.LoadTable(client, "ProductCatalog");
Note

In general, you use the LoadTable method once at the beginning of your application because it makes a DescribeTable call that adds to the round trip to DynamoDB.

You can then use the Table object to perform various data operations. Each data operation has two types of overloads: One takes the minimum required parameters and the other takes optional, operation-specific configuration information. For example, to retrieve an item, you must provide the table's primary key value, in which case you can use the following GetItem overload.

Example

// Get the item from a table that has a primary key that is composed of only a partition key. Table.GetItem(Primitive partitionKey); // Get the item from a table whose primary key is composed of both a partition key and sort key. Table.GetItem(Primitive partitionKey, Primitive sortKey);

You also can pass optional parameters to these methods. For example, the preceding GetItem returns the entire item including all its attributes. You can optionally specify a list of attributes to retrieve. In this case, you use the following GetItem overload that takes in the operation-specific configuration object parameter.

Example

// Configuration object that specifies optional parameters. GetItemOperationConfig config = new GetItemOperationConfig() { AttributesToGet = new List<string>() { "Id", "Title" }, }; // Pass in the configuration to the GetItem method. // 1. Table that has only a partition key as primary key. Table.GetItem(Primitive partitionKey, GetItemOperationConfig config); // 2. Table that has both a partition key and a sort key. Table.GetItem(Primitive partitionKey, Primitive sortKey, GetItemOperationConfig config);

You can use the configuration object to specify several optional parameters such as request a specific list of attributes or specify the page size (number of items per page). Each data operation method has its own configuration class. For example, you can use the GetItemOperationConfig class to provide options for the GetItem operation. You can use the PutItemOperationConfig class to provide optional parameters for the PutItem operation.

The following sections discuss each of the data operations that are supported by the Table class.

Putting an Item - Table.PutItem Method

The PutItem method uploads the input Document instance to the table. If an item that has a primary key that is specified in the input Document exists in the table, the PutItem operation replaces the entire existing item. The new item is identical to the Document object that you provided to the PutItem method. If your original item had any extra attributes, they are no longer present in the new item.

The following are the steps to put a new item into a table using the AWS SDK for .NET document model.

  1. Run the Table.LoadTable method that provides the table name in which you want to put an item.

  2. Create a Document object that has a list of attribute names and their values.

  3. Run Table.PutItem by providing the Document instance as a parameter.

The following C# code example demonstrates the preceding tasks. The example uploads an item to the ProductCatalog table.

Example

Table table = Table.LoadTable(client, "ProductCatalog"); var book = new Document(); book["Id"] = 101; book["Title"] = "Book 101 Title"; book["ISBN"] = "11-11-11-11"; book["Authors"] = new List<string> { "Author 1", "Author 2" }; book["InStock"] = new DynamoDBBool(true); book["QuantityOnHand"] = new DynamoDBNull(); table.PutItem(book);

In the preceding example, the Document instance creates an item that has Number, String, String Set, Boolean, and Null attributes. (Null is used to indicate that the QuantityOnHand for this product is unknown.) For Boolean and Null, use the constructor methods DynamoDBBool and DynamoDBNull.

In DynamoDB, the List and Map data types can contain elements composed of other data types. Here is how to map these data types to the document model API:

  • List — use the DynamoDBList constructor.

  • Map — use the Document constructor.

You can modify the preceding example to add a List attribute to the item. To do this, use a DynamoDBList constructor, as shown in the following code example.

Example

Table table = Table.LoadTable(client, "ProductCatalog"); var book = new Document(); book["Id"] = 101; /*other attributes omitted for brevity...*/ var relatedItems = new DynamoDBList(); relatedItems.Add(341); relatedItems.Add(472); relatedItems.Add(649); book.Add("RelatedItems", relatedItems); table.PutItem(book);

To add a Map attribute to the book, you define another Document. The following code example illustrates how to do this.

Example

Table table = Table.LoadTable(client, "ProductCatalog"); var book = new Document(); book["Id"] = 101; /*other attributes omitted for brevity...*/ var pictures = new Document(); pictures.Add("FrontView", "http://example.com/products/101_front.jpg" ); pictures.Add("RearView", "http://example.com/products/101_rear.jpg" ); book.Add("Pictures", pictures); table.PutItem(book);

These examples are based on the item shown in Specifying Item Attributes When Using Expressions. The document model lets you create complex nested attributes, such as the ProductReviews attribute shown in the case study.

Specifying Optional Parameters

You can configure optional parameters for the PutItem operation by adding the PutItemOperationConfig parameter. For a complete list of optional parameters, see PutItem. The following C# code example puts an item in the ProductCatalog table. It specifies the following optional parameter:

  • The ConditionalExpression parameter to make this a conditional put request. The example creates an expression that specifies the ISBN attribute must have a specific value that has to be present in the item that you are replacing.

Example

Table table = Table.LoadTable(client, "ProductCatalog"); var book = new Document(); book["Id"] = 555; book["Title"] = "Book 555 Title"; book["Price"] = "25.00"; book["ISBN"] = "55-55-55-55"; book["Name"] = "Item 1 updated"; book["Authors"] = new List<string> { "Author x", "Author y" }; book["InStock"] = new DynamoDBBool(true); book["QuantityOnHand"] = new DynamoDBNull(); // Create a condition expression for the optional conditional put operation. Expression expr = new Expression(); expr.ExpressionStatement = "ISBN = :val"; expr.ExpressionAttributeValues[":val"] = "55-55-55-55"; PutItemOperationConfig config = new PutItemOperationConfig() { // Optional parameter. ConditionalExpression = expr }; table.PutItem(book, config);