# KeysAndAttributes
<a name="API_KeysAndAttributes"></a>

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.

## Contents
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**Note**  
In the following list, the required parameters are described first.

 ** Keys **   <a name="DDB-Type-KeysAndAttributes-Keys"></a>
The primary key attribute values that define the items and the attributes associated with the items.  
Type: Array of string to [AttributeValue](API_AttributeValue.md) object maps  
Array Members: Minimum number of 1 item. Maximum number of 100 items.  
Key Length Constraints: Maximum length of 65535.  
Required: Yes

 ** AttributesToGet **   <a name="DDB-Type-KeysAndAttributes-AttributesToGet"></a>
This is a legacy parameter. Use `ProjectionExpression` instead. For more information, see [Legacy Conditional Parameters](https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/LegacyConditionalParameters.html) in the *Amazon DynamoDB Developer Guide*.  
Type: Array of strings  
Array Members: Minimum number of 1 item.  
Length Constraints: Maximum length of 65535.  
Required: No

 ** ConsistentRead **   <a name="DDB-Type-KeysAndAttributes-ConsistentRead"></a>
The consistency of a read operation. If set to `true`, then a strongly consistent read is used; otherwise, an eventually consistent read is used.  
Type: Boolean  
Required: No

 ** ExpressionAttributeNames **   <a name="DDB-Type-KeysAndAttributes-ExpressionAttributeNames"></a>
One or more substitution tokens for attribute names in an expression. The following are some use cases for using `ExpressionAttributeNames`:  
+ 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 **\$1** character in an expression to dereference an attribute name. For example, consider the following attribute name:  
+  `Percentile` 
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](https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/ReservedWords.html) in the *Amazon DynamoDB Developer Guide*). To work around this, you could specify the following for `ExpressionAttributeNames`:  
+  `{"#P":"Percentile"}` 
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](https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Expressions.AccessingItemAttributes.html) in the *Amazon DynamoDB Developer Guide*.  
Type: String to string map  
Value Length Constraints: Maximum length of 65535.  
Required: No

 ** ProjectionExpression **   <a name="DDB-Type-KeysAndAttributes-ProjectionExpression"></a>
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 the `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](https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Expressions.AccessingItemAttributes.html) in the *Amazon DynamoDB Developer Guide*.  
Type: String  
Required: No

## See Also
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For more information about using this API in one of the language-specific AWS SDKs, see the following:
+  [AWS SDK for C\$1\$1](https://docs.aws.amazon.com/goto/SdkForCpp/dynamodb-2012-08-10/KeysAndAttributes) 
+  [AWS SDK for Java V2](https://docs.aws.amazon.com/goto/SdkForJavaV2/dynamodb-2012-08-10/KeysAndAttributes) 
+  [AWS SDK for Ruby V3](https://docs.aws.amazon.com/goto/SdkForRubyV3/dynamodb-2012-08-10/KeysAndAttributes)