Comprehensive and Detailed In-Depth Explanation:
In Appian, when creating a Web API, parameters passed in the URL (e.g., query parameters) are accessed within the Web API expression using the httpRequest object. The URL https://exampleappiancloud.com/suite/webapi/user_management/users?username=john.smith includes a query parameter username with the value john.smith. Appian's Web API documentation specifies how to handle such parameters in the expression rule associated with the Web API.
Option D (httpRequest.queryParameters.username):
This is the correct syntax. The httpRequest.queryParameters object contains all query parameters from the URL. Since username is a single query parameter, you access it directly as httpRequest.queryParameters.username. This returns the value john.smith as a text string, which can then be used in the Web API logic (e.g., to query a user record). Appian's expression language treats query parameters as key-value pairs under queryParameters, making this the standard approach.
Option A (httpRequest.queryParameters.users.username):
This is incorrect. The users part suggests a nested structure (e.g., users as a parameter containing a username subfield), which does not match the URL. The URL only defines username as a top-level query parameter, not a nested object.
Option B (httpRequest.users.username):
This is invalid. The httpRequest object does not have a direct users property. Query parameters are accessed via queryParameters, and there's no indication of a users object in the URL or Appian's Web API model.
Option C (httpRequest.formData.username):
This is incorrect. The httpRequest.formData object is used for parameters passed in the body of a POST or PUT request (e.g., form submissions), not for query parameters in a GET request URL. Since the username is part of the query string (?username=john.smith), formData does not apply.
The correct syntax leverages Appian's standard handling of query parameters, ensuring the Web API can process the username value effectively.