Using expressions in DynamoDB
In Amazon DynamoDB, you can use expressions to specify which attributes to read from an item, write data when a condition is met, specify how to update an item, define queries and filter the results of a query.
This table describes the basic expression grammar and the available kinds of expressions.
| Expression type | Description |
|---|---|
| Projection expression | A projection expression identifies the attributes that you want to retrieve from an item when you use operations such as GetItem, Query, or Scan. |
| Condition expression | A condition expression determines which items should be modified when you use the PutItem, UpdateItem, and DeleteItem operations. |
| Update expression | An update expression specifies how UpdateItem will modify the attributes of an item— for example, setting a scalar value or removing elements from a list or a map. |
| Key condition expression | A key condition expression determines which items a query will read from a table or index. |
| Filter expression | A filter expression determines which items among the Query results should be returned to you. All the other results are discarded. |
For information about expression syntax and more detailed information about each type of expression, see the following sections.
Topics
Note
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.