Differences between queryStringParameters and multiValueQueryStringParameters in AWS Lambda

environment

Python3.7 With proxy integration

Use queryStringParameters

You can get the parameters from the payload passed from API Gateway to Lambda.

request https://XXXX/XXXX/XXXX?id=1&value=foo

response = event.get('queryStringParameters')

return {
    'statusCode': 200,
    'body': json.dumps(response)
}

result

{
    "id": "1"
    "value": "foo"
}

You can get the value by the parameter name.

request https://XXXX/XXXX/XXXX?id=1&value=foo

response = event.get('queryStringParameters').get('value')

return {
    'statusCode': 200,
    'body': json.dumps(response)
}

result

"foo"

It will be null if the specified parameter name does not exist.

Use multiValueQueryStringParameters

You can also get the parameters here, It is used when there are multiple (array) of the same parameter name.

request https://XXXX/XXXX/XXXX?id=1&value=foo&value=bar&value=baz

response = event["multiValueQueryStringParameters"].get("value")

return {
    'statusCode': 200,
    'body': json.dumps(response)
}

result

{
    "id": [
        "1"
    ],
    "value": [
        "foo",
        "bar",
        "baz"
    ]
}

You have to be careful When you specify a parameter name that does not exist If you try to get the contents of the array as it is, an error will occur.

request https://XXXX/XXXX/XXXX?id=1

This is ok (will be null)

response = event["multiValueQueryStringParameters"].get("value")

return {
    'statusCode': 200,
    'body': json.dumps(response)
}

This is an error Let's stop this way of taking.

response = event["multiValueQueryStringParameters"].get("value")[0]

return {
    'statusCode': 200,
    'body': json.dumps(response)
}

When retrieving multiple (array) same parameter names with queryStringParameters

request https://XXXX/XXXX/XXXX?id=1&value=foo&value=bar&value=baz

response = event.get('queryStringParameters')

return {
    'statusCode': 200,
    'body': json.dumps(response)
}

result

{
    "id": "1"
    "value": "baz"
}

The baz is retrieved, overwritten with the last value.

Summary

Let's take the method that suits the purpose according to the parameters passed.