A sample of a controller action receiving an "expand" query parameter that enable returning detailed data

ExpandableController.cs

using System.Collections.Generic;
using System.Linq;
using System.Web.Http;

namespace WebApplication2.Controllers
{
    [Route("api/entities")]
    public class ExpandableController : ApiController
    {
        [HttpGet]
        public IHttpActionResult Get([FromUri] string expand = null)
        {
            var entity = new Entity
            {
                Id = 1,
                Name = "John Doe",
            };

            if (!string.IsNullOrWhiteSpace(expand))
            {
                var expandedRequest = expand.Split(',');
                (bool valid, IEnumerable<string> properties) = ParseExpandedPropertiesRequest(expandedRequest, Entity.GetExpandables());

                if (!valid)
                {
                    // return conflict with some data indicating which properties are wrong..
                    // https://httpstatuses.com/409
                    return Conflict();
                }

                // we have the properties we want to expand.. now just need to pass them and change the queries accordingly. 
            }

            return Ok(entity);
        }

        /// <summary>
        /// Validates and parses the properties the caller wants to "expand"
        /// </summary>
        /// <param name="requestedPropertiesToExpand"></param>
        /// <param name="expandables"></param>
        /// <returns></returns>
        private (bool valid, IEnumerable<string> properties) ParseExpandedPropertiesRequest(
            string[] requestedPropertiesToExpand,
            IEnumerable<string> expandables)
        {
            if (!requestedPropertiesToExpand.Any())
                return (false, Enumerable.Empty<string>());

            var loweredRequestedProperties = requestedPropertiesToExpand.Select(p => p.ToLower()).ToList();
            var allowedExpandableProperties = expandables.Select(p => p.ToLower()).ToList();
            
            if (!loweredRequestedProperties.All(p => allowedExpandableProperties.Contains(p)))
                return (false, Enumerable.Empty<string>());

            // extract the "diff", returning only the properties requested by the caller
            var requestedExpanded = allowedExpandableProperties.Where(x => loweredRequestedProperties.Contains(x)).Select(p => p);

            return (true, requestedExpanded);
        }
    }

    public sealed class Entity
    {
        public int Id { get; set; }
        public string Name { get; set; }

        public string Measurements { get; set; }

        public string Logs { get; set; }

        public string OtherProperty { get; set; }

        public IEnumerable<string> Expandables => GetExpandables();

        /// <summary>
        /// All classes that we want to provide the "expand" functionality
        /// needs to implement this static method
        /// </summary>
        /// <see href="https://developer.atlassian.com/server/confluence/expansions-in-the-rest-api/"/>
        /// <returns></returns>
        internal static IEnumerable<string> GetExpandables()
        {
            return new[]
            {
                nameof(Measurements),
                nameof(Logs),
                nameof(OtherProperty)
            };
        }
    }
}