Expression attribute values - Amazon DynamoDB
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Expression attribute values

If you need to compare an attribute with a value, define an expression attribute value as a placeholder. Expression attribute values in Amazon DynamoDB are substitutes for the actual values that you want to compare—values that you might not know until runtime. An expression attribute value must begin with a colon (:) and be followed by one or more alphanumeric characters.

For example, suppose that you wanted to return all of the ProductCatalog items that are available in Black and cost 500 or less. You could use a Scan operation with a filter expression, as in this Amazon Command Line Interface (Amazon CLI) example.

aws dynamodb scan \ --table-name ProductCatalog \ --filter-expression "contains(Color, :c) and Price <= :p" \ --expression-attribute-values file://values.json

The arguments for --expression-attribute-values are stored in the values.json file.

{ ":c": { "S": "Black" }, ":p": { "N": "500" } }

A Scan operation reads every item in a table. So you should avoid using Scan with large tables.

The filter expression is applied to the Scan results, and items that don't match the filter expression are discarded.

If you define an expression attribute value, you must use it consistently throughout the entire expression. Also, you can't omit the : symbol.

Expression attribute values are used with key condition expressions, condition expressions, update expressions, and filter expressions.


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