Using Expressions in DynamoDB
In Amazon DynamoDB, you use expressions to denote the attributes that you want to read from an item. You also use expressions when writing an item, to indicate any conditions that must be met (also known as a conditional update), and to indicate how the attributes are to be updated. This section describes the basic expression grammar and the available kinds of expressions.
For backward compatibility, DynamoDB also supports conditional parameters that do not use expressions. For more information, see Legacy Conditional Parameters.
New applications should use expressions rather than the legacy parameters.