Represents a set of primary keys and, for each key, the attributes to retrieve from the table.
For each primary key, you must provide all of the key attributes. For example, with a simple primary key, you only need to provide the partition key. For a composite primary key, you must provide both the partition key and the sort key.
This is a legacy parameter. Use
ProjectionExpression instead. For more
information, see Legacy
Conditional Parameters in the Amazon DynamoDB Developer
The consistency of a read operation. If set to
true, then a strongly
consistent read is used; otherwise, an eventually consistent read is used.
One or more substitution tokens for attribute names in an expression. The following
are some use cases for using
To access an attribute whose name conflicts with a DynamoDB reserved word.
To create a placeholder for repeating occurrences of an attribute name in an expression.
To prevent special characters in an attribute name from being misinterpreted in an expression.
Use the # character in an expression to dereference an attribute name. For example, consider the following attribute name:
The name of this attribute conflicts with a reserved word, so it cannot be used
directly in an expression. (For the complete list of reserved words, see Reserved Words in the Amazon DynamoDB Developer
Guide). To work around this, you could specify the following for
You could then use this substitution in an expression, as in this example:
#P = :val
Tokens that begin with the : character are expression attribute values, which are placeholders for the actual value at runtime.
For more information on expression attribute names, see Accessing Item Attributes in the Amazon DynamoDB Developer Guide.
The primary key attribute values that define the items and the attributes associated with the items.
A string that identifies one or more attributes to retrieve from the table. These
attributes can include scalars, sets, or elements of a JSON document. The attributes in
ProjectionExpression must be separated by commas.
If no attribute names are specified, then all attributes will be returned. If any of the requested attributes are not found, they will not appear in the result.
For more information, see Accessing Item Attributes in the Amazon DynamoDB Developer Guide.