Projection expressions - Amazon DynamoDB
Services or capabilities described in Amazon Web Services documentation might vary by Region. To see the differences applicable to the China Regions, see Getting Started with Amazon Web Services in China.

Projection expressions

To read data from a table, you use operations such as GetItem, Query, or Scan. Amazon DynamoDB returns all the item attributes by default. To get only some, rather than all of the attributes, use a projection expression.

A projection expression is a string that identifies the attributes that you want. To retrieve a single attribute, specify its name. For multiple attributes, the names must be comma-separated.

The following are some examples of projection expressions, based on the ProductCatalog item from Specifying item attributes when using expressions:

  • A single top-level attribute.


  • Three top-level attributes. DynamoDB retrieves the entire Color set.

    Title, Price, Color

  • Four top-level attributes. DynamoDB returns the entire contents of RelatedItems and ProductReviews.

    Title, Description, RelatedItems, ProductReviews

You can use any attribute name in a projection expression, provided that the first character is a-z or A-Z and the second character (if present) is a-z, A-Z, or 0-9. If an attribute name does not meet this requirement, you must define an expression attribute name as a placeholder. For more information, see Expression attribute names in DynamoDB.

The following Amazon CLI example shows how to use a projection expression with a GetItem operation. This projection expression retrieves a top-level scalar attribute (Description), the first element in a list (RelatedItems[0]), and a list nested within a map (ProductReviews.FiveStar).

aws dynamodb get-item \ --table-name ProductCatalog \ --key file://key.json \ --projection-expression "Description, RelatedItems[0], ProductReviews.FiveStar"

The arguments for --key are stored in the key.json file.

{ "Id": { "N": "123" } }

For programming language-specific code examples, see Getting started with DynamoDB and Amazon SDKs.