What is a projection expression?

What is 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.

What is projection DynamoDB?

Projections consist of an attribute set copied from table to secondary index. A Projection always occurs with the table partition key and sort key. In queries, projections allow DynamoDB access to any attribute of the projection; they essentially exist as their own table.

What is LastEvaluatedKey?

LastEvaluatedKey. The primary key of the item where the operation stopped, inclusive of the previous result set. Use this value to start a new operation, excluding this value in the new request. If LastEvaluatedKey is empty, then the “last page” of results has been processed and there is no more data to be retrieved.

What is filter expression in DynamoDB?

A filter expression determines which items within the Query results should be returned to you. All of the other results are discarded. A filter expression is applied after a Query finishes, but before the results are returned.

What is Keyconditionexpression in DynamoDB?

The condition can optionally perform one of several comparison tests on a single sort key value. This allows Query to retrieve one item with a given partition key value and sort key value, or several items that have the same partition key value but different sort key values.

What is projection in GSI DynamoDB?

A projection is the set of attributes that is copied from a table into a secondary index. The partition key and sort key of the table are always projected into the index; you can project other attributes to support your application’s query requirements.

What is DynamoDBIndexHashKey?

Annotation Type DynamoDBIndexHashKey Annotation for marking a property in a class as the attribute to be used as the hash key for one or more global secondary indexes on a DynamoDB table. This annotation is required if this attribute will be used as index key for item queries.

What is ScanIndexForward?

ScanIndexForward is the correct way to get items in descending order by the range key of the table or index you are querying. From the AWS API Reference: A value that specifies ascending (true) or descending (false) traversal of the index.

What is Expressionattributevalues?

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.

What is scan DynamoDB?

A Scan operation in Amazon DynamoDB reads every item in a table or a secondary index. By default, a Scan operation returns all of the data attributes for every item in the table or index. Optionally, DynamoDB can apply a filter expression to this data, narrowing the results before they are returned to the user.

What is partition key in DynamoDB?

Partition key – A simple primary key, composed of one attribute known as the partition key. DynamoDB uses the partition key’s value as input to an internal hash function. The output from the hash function determines the partition (physical storage internal to DynamoDB) in which the item will be stored.