When reading objects in DynamoDB using the GetItem
, Scan
,
Query
, BatchGetItem
, and TransactGetItems
operations, you can optionally specify a projection that identifies the attributes that you
want. The projection property has the following structure, which is similar to filters:
type DynamoDBExpression = {
expression: string;
expressionNames?: { [key: string]: string}
};
The fields are defined as follows:
-
expression
-
The projection expression, which is a string. To retrieve a single attribute, specify its name. For multiple attributes, the names must be comma-separated values. For more information on writing projection expressions, see the DynamoDB projection expressions documentation. This field is required.
-
expressionNames
-
The substitutions for expression attribute name placeholders in the form of key-value pairs. The key corresponds to a name placeholder used in the
expression
. The value must be a string that corresponds to the attribute name of the item in DynamoDB. This field is optional and should only be populated with substitutions for expression attribute name placeholders used in theexpression
. For more information aboutexpressionNames
, see the DynamoDB documentation.
Example 1
The following example is a projection section for a JavaScript function in which only
the attributes author
and id
are returned from DynamoDB:
projection : {
expression : "#author, id",
expressionNames : {
"#author" : "author"
}
}
Tip
You can access your GraphQL request selection set using selectionSetList. This field allows you to frame your projection expression dynamically according to your requirements.
Note
While using projection expressions with the Query
and
Scan
operations, the value for select
must be
SPECIFIC_ATTRIBUTES
. For more information, see the DynamoDB documentation.