Fix deserialization of (typed-table) similarity when reading rows

src/DataStax.AstraDB.DataApi/Core/Query/FindEnumerator.cs

@@ -124,6 +124,10 @@ public FindEnumerator<T, TResult, TSort> Sort(TSort sortBuilder)
     /// var similarity = result.Similarity;
     /// </code>
     /// </example>
+    /// <remarks>
+    /// When searching on Tables, the field in the row class should be given the
+    /// attribute <see cref="SerDes.ColumnMappingAttribute"/> instead.
+    /// </remarks>
     public FindEnumerator<T, TResult, TSort> IncludeSimilarity(bool includeSimilarity)
     {
         return UpdateOptions(options => options.IncludeSimilarity = includeSimilarity);

src/DataStax.AstraDB.DataApi/SerDes/ColumnMappingAttribute.cs

@@ -0,0 +1,40 @@
+/*
+ * Copyright DataStax, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+namespace DataStax.AstraDB.DataApi.SerDes;
+
+using System;
+
+/// <summary>
+/// Marks a property on a table row as a special field for the database's use.
+/// </summary>
+[AttributeUsage(AttributeTargets.Property | AttributeTargets.Field, AllowMultiple = false)]
+public class ColumnMappingAttribute : Attribute
+{
+    /// <summary>
+    /// The type of special field this property is mapped to
+    /// </summary>
+    public ColumnMappingField Field { get; }
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="ColumnMappingAttribute"/> class.
+    /// </summary>
+    /// <param name="field">The type of special field this property is mapped to</param>
+    public ColumnMappingAttribute(ColumnMappingField field)
+    {
+        Field = field;
+    }
+}

src/DataStax.AstraDB.DataApi/SerDes/ColumnMappingField.cs

@@ -0,0 +1,26 @@
+/*
+ * Copyright DataStax, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+namespace DataStax.AstraDB.DataApi.SerDes;
+
+/// <summary>
+/// Special field types for table rows.
+/// </summary>
+public enum ColumnMappingField
+{
+    /// <summary>On read operations only, deserializes the similarity result for vector comparisons</summary>
+    Similarity,
+}

src/DataStax.AstraDB.DataApi/SerDes/DocumentMappingAttribute.cs

@@ -19,7 +19,7 @@ namespace DataStax.AstraDB.DataApi.SerDes;
 using System;
 
 /// <summary>
-/// Marks a property on a document as a special field for the database's use.
+/// Marks a property on a collection document as a special field for the database's use.
 /// </summary>
 [AttributeUsage(AttributeTargets.Property | AttributeTargets.Field, AllowMultiple = false)]
 public class DocumentMappingAttribute : Attribute

src/DataStax.AstraDB.DataApi/SerDes/DocumentMappingField.cs

@@ -17,7 +17,7 @@
 namespace DataStax.AstraDB.DataApi.SerDes;
 
 /// <summary>
-/// Special field types
+/// Special field types for collection documents.
 /// </summary>
 public enum DocumentMappingField
 {

src/DataStax.AstraDB.DataApi/SerDes/RowConverter.cs

@@ -40,7 +40,9 @@ public override T Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerial
 
         T instance = Activator.CreateInstance<T>();
         var properties = typeof(T).GetProperties(BindingFlags.Public | BindingFlags.Instance)
-            .Where(p => p.CanWrite && !p.GetCustomAttributes<ColumnIgnoreAttribute>().Any())
+            .Where(p => p.CanWrite && 
+                (!p.GetCustomAttributes<ColumnIgnoreAttribute>().Any() ||
+                p.GetCustomAttribute<ColumnMappingAttribute>()?.Field == ColumnMappingField.Similarity))
             .ToDictionary(p => GetPropertyName(p, true), p => p);
 
         while (reader.Read())
@@ -228,10 +230,10 @@ public override void Write(Utf8JsonWriter writer, T value, JsonSerializerOptions
 
     private static string GetPropertyName(PropertyInfo property, bool forDeserialization)
     {
-        var documentMappingAttribute = property.GetCustomAttribute<DocumentMappingAttribute>();
-        if (documentMappingAttribute != null && forDeserialization)
+        var columnMappingAttribute = property.GetCustomAttribute<ColumnMappingAttribute>();
+        if (columnMappingAttribute != null && forDeserialization)
         {
-            if (documentMappingAttribute.Field == DocumentMappingField.Similarity)
+            if (columnMappingAttribute.Field == ColumnMappingField.Similarity)
             {
                 return "$similarity";
             }

test/DataStax.AstraDB.DataApi.IntegrationTests/TestObjects.cs

@@ -19,7 +19,7 @@ public class SimpleObjectWithVector
 
 public class SimpleObjectWithVectorSearchResult : SimpleObjectWithVector
 {
-    [DocumentMapping(DocumentMappingField.Similarity)]
+    [ColumnMapping(ColumnMappingField.Similarity)]
     public double? Similarity { get; set; }
 }
 
@@ -225,7 +225,7 @@ public class RowEventByDay
 
 public class RowBookWithSimilarity : RowBook
 {
-    [DocumentMapping(DocumentMappingField.Similarity)]
+    [ColumnMapping(ColumnMappingField.Similarity)]
     public double Similarity { get; set; }
 }
 

test/DataStax.AstraDB.DataApi.IntegrationTests/Tests/AdditionalTableTests.cs

@@ -553,7 +553,8 @@ public async Task FindOne_Vector()
             var result = await table.FindOneAsync<SimpleObjectWithVectorSearchResult>(null,
                 new TableFindOptions<SimpleObjectWithVector>() { Sort = sort, IncludeSimilarity = true });
 
-            Assert.NotEqual(0, result.Similarity);
+            Assert.NotNull(result.Similarity);
+            Assert.True(result.Similarity > 0);
         }
         finally
         {