# LeftExpression
<a name="API_LeftExpression"></a>

Left expression of the event metadata filter.

## Contents
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**Important**  
This data type is a UNION, so only one of the following members can be specified when used or returned.

 ** metadataKey **   <a name="BedrockAgentCore-Type-LeftExpression-metadataKey"></a>
Key associated with the metadata in an event.  
Type: String  
Length Constraints: Minimum length of 1. Maximum length of 128.  
Pattern: `[a-zA-Z0-9\s._:/=+@-]*`   
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\+\+](https://docs.aws.amazon.com/goto/SdkForCpp/bedrock-agentcore-2024-02-28/LeftExpression) 
+  [AWS SDK for Java V2](https://docs.aws.amazon.com/goto/SdkForJavaV2/bedrock-agentcore-2024-02-28/LeftExpression) 
+  [AWS SDK for Ruby V3](https://docs.aws.amazon.com/goto/SdkForRubyV3/bedrock-agentcore-2024-02-28/LeftExpression)