Using expression attribute values in DynamoDB - Amazon DynamoDB

Using expression attribute values in DynamoDB

Expression attribute values in Amazon DynamoDB act as variables. They're 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 AWS Command Line Interface (AWS 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" }
}

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.