AspNetCoreCustomODataQueryAttribute.cs

using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.Filters;
using Microsoft.AspNet.OData;
using Microsoft.AspNet.OData.Extensions;
using Microsoft.AspNet.OData.Query;
using System.Linq;
using System;
using Newtonsoft.Json;

namespace R.Web.Api
{
	/// <summary>
	/// Replacement for Microsoft.AspNet.OData.EnableQueryAttribute that returns a valid OData response, see: ODataPagedResult.
	/// </summary>
	public class ODataQueryable : EnableQueryAttribute
	{
		public override IQueryable ApplyQuery(IQueryable queryable, ODataQueryOptions queryOptions)
		{
			// NOTE: altering OData query:
			// https://d-fens.ch/2017/02/26/modifying-odataqueryoptions-on-the-fly/
			// https://tutel.me/c/programming/questions/33660648/odata+v4+modify+filter+on+server+side
			var baseResult = base.ApplyQuery(queryable, queryOptions);
			return baseResult;
		}

		public override void OnActionExecuted(ActionExecutedContext actionExecutedContext)
		{
			// NOTE:
			// issue https://github.com/OData/WebApi/issues/159
			// workaround: https://stackoverflow.com/questions/27545207/items-count-in-odata-v4-webapi-response

			base.OnActionExecuted(actionExecutedContext);

			// Skip post processing on exceptions...
			if (actionExecutedContext.Exception != null)
				return;

			// ...and on errors
			var response = actionExecutedContext.HttpContext.Response;
			if (response == null || !response.IsSuccessStatusCode() || actionExecutedContext.Result == null)
				return;

			//
			// Post-process
			var responseContent = actionExecutedContext.Result as ObjectResult;

			var items = responseContent?.Value as IQueryable;
			if (items == null)
				throw new NotSupportedException($"Controller action result with OData queries applied has to be an IQueryable<>, returned type is: {responseContent?.Value?.GetType()}!");

			// NOTE: if below does not work, we can try: count = long.Parse(Request.Properties["System.Web.OData.TotalCount"]‌​.ToString())
			var nextLink = actionExecutedContext.HttpContext.Request.ODataFeature().NextLink;
			var count = actionExecutedContext.HttpContext.Request.ODataFeature().TotalCount;

			responseContent.Value = new ODataPagedResult(items, nextLink, count);
		}
	}

	/// <summary>
	/// NOTE: theres a PageResult<T> class already in .NET but it does not serialize via JSON as proper OData result...
	/// </summary>
	public class ODataPagedResult
	{
		public ODataPagedResult(IQueryable items, Uri nextLink, long? count)
		{
			Value = items;
			NextLink = nextLink?.ToString() ?? "";
			Count = count;
		}

		[JsonProperty("value")]
		public IQueryable Value { get; set; }
		[JsonProperty("@odata.count")]
		public long? Count { get; set; }
		[JsonProperty("@odata.nextLink")]
		public string NextLink { get; set; }
	}
}