How do I map AWS API Gateway query string to C# AWS Lambda function?

Question

I have a C# lambda function that is called from API gateway using a GET request.

[LambdaSerializer(typeof(Amazon.Lambda.Serialization.Json.JsonSerializer))]
public ResponseModel MyFunction(RequestModel request)
{
    return new ResponseModel { body = "Hello world!" };
}

public class RequestModel 
{
    [JsonProperty("a")]
    public string A { get; set; }

    [JsonProperty("b")]
    public string B { get; set; }
}

public class ResponseModel 
{
    public int statusCode { get; set; } = 200;
    public object headers { get; set; } = new object();
    public string body { get; set; } = "";
}

How do I map the query string parameters sent to API gateway to the RequestModel parameter in MyFunction ?

I have called the function with parameters but they don't seem to come through. Is there a wait to achieve this with a C# lambda function?

Thanks,

Chris

Answer 1

Try putting this in your RequestModel :

public class RequestModel 
{
   [JsonProperty("queryStringParameters")]
   public Dictionary<string, string> QueryStringParameters { get; set; }
}

Then access the query string values as request.QueryStringParameters["foo"] , etc.

If you checked the Use Lambda Proxy integration box in API Gateway for your resource and method (which I suspect you did, since you've structured your response object with the statusCode , headers , and body fields), the corresponding request object structure is documented in Input Format of a Lambda Function for Proxy Integration , buried deep in AWS's documentation. There are also other fields available like the body, headers, HTTP verb, etc.

My understanding is that you can also create a custom Payload Mapping to map different parts of the request to a custom JSON object, but doing so requires more configuration than using the built-in Lambda Proxy.