public void setProjectionExpression(String projectionExpression) {
        this.projectionExpression = projectionExpression;
    }
<p>
A string that identifies one or more attributes to retrieve from the specified table or index. These attributes
can include scalars, sets, or elements of a JSON document. The attributes in the expression must be separated by
commas.
</p>
<p>
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.
</p>
<p>
For more information, see <a href=
"https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Expressions.AccessingItemAttributes.html"
>Specifying Item Attributes</a> in the <i>Amazon DynamoDB Developer Guide</i>.
</p>

@param projectionExpression
       A string that identifies one or more attributes to retrieve from the specified table or index. These
       attributes can include scalars, sets, or elements of a JSON document. The attributes in the expression
       must be separated by commas.</p>
       <p>
       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.
       </p>
       <p>
       For more information, see <a href=
       "https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Expressions.AccessingItemAttributes.html"
       >Specifying Item Attributes</a> in the <i>Amazon DynamoDB Developer Guide</i>.
aws-java-sdk-dynamodb/src/main/java/com/amazonaws/services/dynamodbv2/model/ScanRequest.java