Scoring in RediSearch (#1254)

* Scoring in RediSearch

* Unit Test Added: EXPLAINSCORE
#1254

src/NRediSearch/Client.cs

@@ -231,7 +231,7 @@ public SearchResult Search(Query q)
             q.SerializeRedisArgs(args);
 
             var resp = (RedisResult[])DbSync.Execute("FT.SEARCH", args);
-            return new SearchResult(resp, !q.NoContent, q.WithScores, q.WithPayloads);
+            return new SearchResult(resp, !q.NoContent, q.WithScores, q.WithPayloads, q.ExplainScore);
         }
 
         /// <summary>
@@ -248,7 +248,7 @@ public async Task<SearchResult> SearchAsync(Query q)
             q.SerializeRedisArgs(args);
 
             var resp = (RedisResult[])await _db.ExecuteAsync("FT.SEARCH", args).ConfigureAwait(false);
-            return new SearchResult(resp, !q.NoContent, q.WithScores, q.WithPayloads);
+            return new SearchResult(resp, !q.NoContent, q.WithScores, q.WithPayloads, q.ExplainScore);
         }
 
         /// <summary>

src/NRediSearch/Document.cs

@@ -13,6 +13,7 @@ public class Document
         public string Id { get; }
         public double Score { get; }
         public byte[] Payload { get; }
+        public string[] ScoreExplained { get; private set; }
         internal readonly Dictionary<string, RedisValue> _properties;
         public Document(string id, double score, byte[] payload) : this(id, null, score, payload) { }
         public Document(string id) : this(id, null, 1.0, null) { }
@@ -42,6 +43,16 @@ public static Document Load(string id, double score, byte[] payload, RedisValue[
             return ret;
         }
 
+        public static Document Load(string id, double score, byte[] payload, RedisValue[] fields, string[] scoreExplained)
+        {
+            Document ret = Document.Load(id, score, payload, fields);
+            if (scoreExplained != null)
+            {
+                ret.ScoreExplained = scoreExplained;
+            }
+            return ret;
+        }
+
         public RedisValue this[string key]
         {
             get { return _properties.TryGetValue(key, out var val) ? val : default(RedisValue); }

src/NRediSearch/Query.cs

@@ -141,6 +141,13 @@ public Paging(int offset, int count)
         /// Set the query language, for stemming purposes; see http://redisearch.io for documentation on languages and stemming
         /// </summary>
         public string Language { get; set; }
+
+        /// <summary>
+        /// Set the query scoring. see https://oss.redislabs.com/redisearch/Scoring.html for documentation
+        /// </summary>
+        public string Scoring { get; set; }
+        public bool ExplainScore { get; set; }
+
         internal string[] _fields = null;
         internal string[] _keys = null;
         internal string[] _returnFields = null;
@@ -231,6 +238,17 @@ internal void SerializeRedisArgs(List<object> args)
                 args.Add((SortAscending ? "ASC" : "DESC").Literal());
             }
 
+            if (Scoring != null)
+            {
+                args.Add("SCORER".Literal());
+                args.Add(Scoring);
+
+                if (ExplainScore)
+                {
+                    args.Add("EXPLAINSCORE".Literal());
+                }
+            }
+
             if (Payload != null)
             {
                 args.Add("PAYLOAD".Literal());
@@ -460,5 +478,28 @@ public Query SetLanguage(string language)
             Language = language;
             return this;
         }
+
+        /// <summary>
+        /// RediSearch comes with a few very basic scoring functions to evaluate document relevance. They are all based on document scores and term frequency.
+        /// This is regardless of the ability to use sortable fields.
+        /// Scoring functions are specified by adding the SCORER {scorer_name} argument to a search query.
+        /// If you prefer a custom scoring function, it is possible to add more functions using the Extension API.
+        /// These are the pre-bundled scoring functions available in RediSearch and how they work.Each function is mentioned by registered name,
+        /// that can be passed as a SCORER argument in FT.SEARCH
+        /// Pre-bundled scoring:
+        /// - TFIDF (default) (https://oss.redislabs.com/redisearch/Scoring.html#tfidf_default)
+        /// - TFIDF.DOCNORM (https://oss.redislabs.com/redisearch/Scoring.html#tfidfdocnorm)
+        /// - BM25 (https://oss.redislabs.com/redisearch/Scoring.html#bm25)
+        /// - DISMAX (https://oss.redislabs.com/redisearch/Scoring.html#dismax)
+        /// - DOCSCORE (https://oss.redislabs.com/redisearch/Scoring.html#docscore)
+        /// - HAMMING (https://oss.redislabs.com/redisearch/Scoring.html#hamming)
+        /// </summary>
+        /// <param name="scoring"></param>
+        /// <returns></returns>
+        public Query SetScoring(string scoring)
+        {
+            Scoring = scoring;
+            return this;
+        }
     }
 }

src/NRediSearch/SearchResult.cs

@@ -2,6 +2,7 @@
 
 using StackExchange.Redis;
 using System.Collections.Generic;
+using System.Linq;
 
 namespace NRediSearch
 {
@@ -15,7 +16,7 @@ public class SearchResult
         public long TotalResults { get; }
         public List<Document> Documents { get; }
 
-        internal SearchResult(RedisResult[] resp, bool hasContent, bool hasScores, bool hasPayloads)
+        internal SearchResult(RedisResult[] resp, bool hasContent, bool hasScores, bool hasPayloads, bool shouldExplainScore)
         {
             // Calculate the step distance to walk over the results.
             // The order of results is id, score (if withScore), payLoad (if hasPayloads), fields
@@ -28,6 +29,7 @@ internal SearchResult(RedisResult[] resp, bool hasContent, bool hasScores, bool
                 step++;
                 scoreOffset = 1;
                 contentOffset++;
+
             }
             if (hasContent)
             {
@@ -50,10 +52,21 @@ internal SearchResult(RedisResult[] resp, bool hasContent, bool hasScores, bool
                 double score = 1.0;
                 byte[] payload = null;
                 RedisValue[] fields = null;
+                string[] scoreExplained = null;
                 if (hasScores)
+                {
+                    if (shouldExplainScore)
+                    {
+                        var scoreResult = (RedisResult[])resp[i + scoreOffset];
+                        score = (double) scoreResult[0];
+                        var redisResultsScoreExplained = (RedisResult[]) scoreResult[1];
+                        scoreExplained = FlatRedisResultArray(redisResultsScoreExplained).ToArray();
+                    }
+                    else
                     {
                         score = (double)resp[i + scoreOffset];
                     }
+                }
                 if (hasPayloads)
                 {
                     payload = (byte[])resp[i + payloadOffset];
@@ -64,7 +77,23 @@ internal SearchResult(RedisResult[] resp, bool hasContent, bool hasScores, bool
                     fields = (RedisValue[])resp[i + contentOffset];
                 }
 
-                docs.Add(Document.Load(id, score, payload, fields));
+                docs.Add(Document.Load(id, score, payload, fields, scoreExplained));
+            }
+        }
+
+        static IEnumerable<string> FlatRedisResultArray(RedisResult[] collection)
+        {
+            foreach (var o in collection)
+            {
+                if (o.Type == ResultType.MultiBulk)
+                {
+                    foreach (string t in FlatRedisResultArray((RedisResult[])o))
+                        yield return t;
+                }
+                else
+                {
+                    yield return o.ToString();
+                }
             }
         }
     }

tests/NRediSearch.Test/ExampleUsage.cs

@@ -77,5 +77,116 @@ public void BasicUsage()
             Assert.Equal("lorem ipsum", (string)item["body"]);
             Assert.Equal(1337, (int)item["price"]);
         }
+
+        [Fact]
+        public void BasicScoringUsage()
+        {
+            var client = GetClient();
+
+            try { client.DropIndex(); } catch { } // reset DB
+
+            CreateSchema(client);
+
+            var term = "petit*";
+
+            var query = new NRediSearch.Query(term);
+            query.Limit(0, 10);
+            query.WithScores = true;
+
+            var searchResult = client.Search(query);
+
+            var docResult = searchResult.Documents.FirstOrDefault();
+
+            Assert.Equal(1, searchResult.TotalResults);
+            Assert.NotEqual(0, docResult.Score);
+            Assert.Equal("1", docResult.Id);
+            Assert.Null(docResult.ScoreExplained);
+        }
+
+        [Fact]
+        public void BasicScoringUsageWithExplainScore()
+        {
+            var client = GetClient();
+
+            try { client.DropIndex(); } catch { } // reset DB
+
+            CreateSchema(client);
+
+            var term = "petit*";
+
+            var query = new NRediSearch.Query(term);
+            query.Limit(0, 10);
+            query.WithScores = true;
+            query.Scoring = "TFIDF";
+            query.ExplainScore = true;
+
+            var searchResult = client.Search(query);
+
+            var docResult = searchResult.Documents.FirstOrDefault();
+
+            Assert.Equal(1, searchResult.TotalResults);
+            Assert.NotEqual(0, docResult.Score);
+            Assert.Equal("1", docResult.Id);
+            Assert.NotEmpty(docResult.ScoreExplained);
+            Assert.Equal("Final TFIDF : words TFIDF 1.00 * document score 1.00 / norm 2 / slop 1", docResult.ScoreExplained[0]);
+            Assert.Equal("(Weight 1.00 * total children TFIDF 1.00)", docResult.ScoreExplained[1]);
+            Assert.Equal("(TFIDF 1.00 = Weight 1.00 * TF 1 * IDF 1.00)", docResult.ScoreExplained[2]);
+        }
+
+        [Fact]
+        public void BasicScoringUsageWithExplainScoreDifferentScorer()
+        {
+            var client = GetClient();
+
+            try { client.DropIndex(); } catch { } // reset DB
+
+            CreateSchema(client);
+
+            var term = "petit*";
+
+            var query = new NRediSearch.Query(term);
+            query.Limit(0, 10);
+            query.WithScores = true;
+            query.Scoring = "TFIDF.DOCNORM";
+            query.ExplainScore = true;
+
+            var searchResult = client.Search(query);
+
+            var docResult = searchResult.Documents.FirstOrDefault();
+
+            Assert.Equal(1, searchResult.TotalResults);
+            Assert.NotEqual(0, docResult.Score);
+            Assert.Equal("1", docResult.Id);
+            Assert.NotEmpty(docResult.ScoreExplained);
+            Assert.Equal("Final TFIDF : words TFIDF 1.00 * document score 1.00 / norm 20 / slop 1", docResult.ScoreExplained[0]);
+            Assert.Equal("(Weight 1.00 * total children TFIDF 1.00)", docResult.ScoreExplained[1]);
+            Assert.Equal("(TFIDF 1.00 = Weight 1.00 * TF 1 * IDF 1.00)", docResult.ScoreExplained[2]);
+        }
+
+        private void CreateSchema(Client client)
+        {
+            var schema = new NRediSearch.Schema();
+
+            schema
+                .AddSortableTextField("title")
+                .AddTextField("country")
+                .AddTextField("author")
+                .AddTextField("aka")
+                .AddTagField("language");
+
+            client.CreateIndex(schema, NRediSearch.Client.IndexOptions.Default);
+
+            var doc = new NRediSearch.Document("1");
+
+            doc
+                .Set("title", "Le Petit Prince")
+                .Set("country", "France")
+                .Set("author", "Antoine de Saint-Exupéry")
+                .Set("language", "fr_FR")
+                .Set("aka", "The Little Prince, El Principito");
+
+            client.AddDocument(doc);
+        }
     }
 }
+

tests/NRediSearch.Test/QueryTest.cs

@@ -35,13 +35,15 @@ public void SerializeRedisArgs()
                 NoStopwords = true,
                 Verbatim = true,
                 WithPayloads = true,
-                WithScores = true
+                WithScores = true,
+                Scoring = "TFIDF.DOCNORM",
+                ExplainScore = true
             };
 
             var args = new List<object>();
             query.SerializeRedisArgs(args);
 
-            Assert.Equal(8, args.Count);
+            Assert.Equal(11, args.Count);
             Assert.Equal(query.QueryString, (string)args[0]);
             Assert.Contains("NOCONTENT".Literal(), args);
             Assert.Contains("NOSTOPWORDS".Literal(), args);
@@ -50,9 +52,15 @@ public void SerializeRedisArgs()
             Assert.Contains("WITHSCORES".Literal(), args);
             Assert.Contains("LANGUAGE".Literal(), args);
             Assert.Contains("", args);
+            Assert.Contains("SCORER".Literal(), args);
+            Assert.Contains("TFIDF.DOCNORM", args);
+            Assert.Contains("EXPLAINSCORE".Literal(), args);
 
             var languageIndex = args.IndexOf("LANGUAGE".Literal());
             Assert.Equal("", args[languageIndex + 1]);
+
+            var scoringIndex = args.IndexOf("SCORER".Literal());
+            Assert.Equal("TFIDF.DOCNORM", args[scoringIndex + 1]);
         }
 
         [Fact]
@@ -168,5 +176,14 @@ public void SummarizeFields()
             Assert.Equal(-1, query._summarizeFragmentLen);
             Assert.Equal(-1, query._summarizeNumFragments);
         }
+
+        [Fact]
+        public void SetScoring()
+        {
+            var query = GetQuery();
+            Assert.Null(query.Scoring);
+            Assert.Same(query, query.SetScoring("TFIDF.DOCNORM"));
+            Assert.Equal("TFIDF.DOCNORM", query.Scoring);
+        }
     }
 }