Episerver Find Explain

ExplainCommand.cs

using System;
using System.IO;
using System.Net;
using System.Text;
using EPiServer.Find;
using EPiServer.Find.Api;
using EPiServer.Find.Connection;
using EPiServer.Find.Helpers;
using EPiServer.Find.Json;
using Newtonsoft.Json.Linq;

namespace EPiServer.Reference.Commerce.Site.Explain
{
    public class ExplainCommand : Command
    {
        private readonly string _index;

        public ExplainCommand(ICommandContext commandContext, string index) : base(commandContext)
        {
            _index = index;
        }

        public ExplainSearchResult Explain(ISearch search)
        {
            var request = CommandContext.RequestFactory.CreateRequest(GetUrl(), HttpVerbs.Post, ExplicitRequestTimeout);

            try
            {
                var context = new SearchContext();
                search.ApplyActions(context);
                var requestBody = CommandContext.Serializer.Serialize(context.RequestBody);
                var jObject = JObject.Parse(requestBody);
                jObject.Add("explain", true);
                request.WriteBody(jObject.ToString());
                return GetResponse<ExplainSearchResult>(request);
            }
            catch (WebException ex)
            {
                var message = ex.Message;

                if (!ex.Response.IsNotNull())
                {
                    throw new WebException(message, ex);
                }

                var end = new StreamReader(ex.Response.GetResponseStream(), Encoding.UTF8).ReadToEnd();
                message = message + Environment.NewLine + end;
                throw new WebException(message, ex);
            }
        }

        private string GetUrl()
        {
            return $"{GetServerUrl()}{_index}/_search";
        }
    }
}

ExplainHitCollection.cs

using System.Collections.Generic;
using Newtonsoft.Json;

namespace EPiServer.Reference.Commerce.Site.Explain
{
    public class ExplainHitCollection
    {
        [JsonProperty("hits")]
        public virtual List<ExplainSearchHit> Hits { get; set; }

        [JsonProperty("total")]
        public int Total { get; set; }
    }
}

ExplainSearchExtensions.cs

using EPiServer.Find;

namespace EPiServer.Reference.Commerce.Site.Explain
{
    public static class ExplainSearchExtensions
    {
        public static ExplainSearchResult GetExplainResult(this ISearch search)
        {
            return search.Client.NewCommand(context => new ExplainCommand(context, search.Client.DefaultIndex))
                .Explain(search);
        }
    }
}

ExplainSearchHit.cs

using EPiServer.Find.Api;
using Newtonsoft.Json;

namespace EPiServer.Reference.Commerce.Site.Explain
{
    [JsonConverter(typeof(ExplainSearchHitConverter))]
    public class ExplainSearchHit : SearchHit
    {
        [JsonProperty("_explanation")]
        public Explanation Explanation { get; set; }

        [JsonIgnore]
        public virtual string DocumentName { get; set; }
    }
}

ExplainSearchHitConverter.cs

using System;
using System.Reflection;
using EPiServer.Find.Json;
using Newtonsoft.Json;
using Newtonsoft.Json.Linq;

namespace EPiServer.Reference.Commerce.Site.Explain
{
    internal class ExplainSearchHitConverter : IgnoredPropertiesHandlingConverterBase
    {
        public override bool CanConvert(Type objectType)
        {
            return true;
        }

        protected override void PopulateProperty(JsonReader reader, JsonSerializer serializer, Type objectType, string propertyName, object item)
        {
            if (propertyName == "fields" || propertyName == "_source")
            {
                PopulateDocumentNameProperty(reader, serializer, objectType, item);
                return;
            }

            if (propertyName == "_explanation")
            {
                PopulateExplanationProperty(reader, serializer, objectType, item);
            }
        }

        private static void PopulateDocumentNameProperty(JsonReader reader, JsonSerializer serializer, Type objectType, object item)
        {
            var obj = serializer.Deserialize<JObject>(reader);
            var documentName = obj["_Name"].Value<string>();

            objectType.InvokeMember("DocumentName",
                BindingFlags.Instance | BindingFlags.Public | BindingFlags.SetProperty, null, item,
                new object[] {documentName});
        }

        private static void PopulateExplanationProperty(JsonReader reader, JsonSerializer serializer, Type objectType, object item)
        {
            var obj = serializer.Deserialize<Explanation>(reader);
            objectType.InvokeMember("Explanation",
                BindingFlags.Instance | BindingFlags.Public | BindingFlags.SetProperty, null, item,
                new object[] {obj});
        }
    }
}

ExplainSearchResult.cs

using Newtonsoft.Json;

namespace EPiServer.Reference.Commerce.Site.Explain
{
    public class ExplainSearchResult
    {
        [JsonProperty("hits")]
        public ExplainHitCollection Hits { get; set; }
    }
}

Explanation.cs

using System.Collections.Generic;
using Newtonsoft.Json;

namespace EPiServer.Reference.Commerce.Site.Explain
{
    public class Explanation
    {
        [JsonProperty("value", NullValueHandling = NullValueHandling.Ignore)]
        public double Value { get; set; }

        [JsonProperty("description")]
        public string Description { get; set; }

        [JsonProperty("details")]
        public List<Explanation> Details { get; set; }
    }
}

Example usage:

var result = _client.Search<IContent>().For(query).GetExplainResult();

Please note: this functionality doesn't work on Episerver Find demo indexes.