CSHARP-5748: Use KeyValuePairSerializer consistently for KeyValuePair (#1785)

Author: rstam

src/MongoDB.Bson/Serialization/Serializers/KeyValuePairSerializer.cs

@@ -29,6 +29,30 @@ public interface IKeyValuePairSerializer
         BsonType Representation { get;  }
     }
 
+    /// <summary>
+    /// Static factory class for KeyValuePairSerializers.
+    /// </summary>
+    public static class KeyValuePairSerializer
+    {
+        /// <summary>
+        /// Creates a KeyValuePairSerializer.
+        /// </summary>
+        /// <param name="representation">The representation.</param>
+        /// <param name="keySerializer">The key serializer.</param>
+        /// <param name="valueSerializer">The value Serializer.</param>
+        /// <returns>A KeyValuePairSerializer.</returns>
+        public static IBsonSerializer Create(
+            BsonType representation,
+            IBsonSerializer keySerializer,
+            IBsonSerializer valueSerializer)
+        {
+            var keyType = keySerializer.ValueType;
+            var valueType = valueSerializer.ValueType;
+            var keyValuePairSerializerType = typeof(KeyValuePairSerializer<,>).MakeGenericType(keyType, valueType);
+            return (IBsonSerializer)Activator.CreateInstance(keyValuePairSerializerType, [representation, keySerializer, valueSerializer]);
+        }
+    }
+
     /// <summary>
     /// Represents a serializer for KeyValuePairs.
     /// </summary>

src/MongoDB.Driver/Linq/Linq3Implementation/Translators/ExpressionToAggregationExpressionTranslators/NewKeyValuePairExpressionToAggregationExpressionTranslator.cs

@@ -16,7 +16,9 @@
 using System;
 using System.Collections.Generic;
 using System.Linq.Expressions;
+using MongoDB.Bson;
 using MongoDB.Bson.Serialization;
+using MongoDB.Bson.Serialization.Serializers;
 using MongoDB.Driver.Linq.Linq3Implementation.Ast.Expressions;
 
 namespace MongoDB.Driver.Linq.Linq3Implementation.Translators.ExpressionToAggregationExpressionTranslators
@@ -43,37 +45,16 @@ public static TranslatedExpression Translate(
             var keyTranslation = ExpressionToAggregationExpressionTranslator.Translate(context, keyExpression);
             var valueTranslation = ExpressionToAggregationExpressionTranslator.Translate(context, valueExpression);
 
-            var serializer = CreateResultSerializer(expression.Type, keyTranslation.Serializer, valueTranslation.Serializer, out var keyElementName, out var valueElementName);
             var ast = AstExpression.ComputedDocument([
-                AstExpression.ComputedField(keyElementName, keyTranslation.Ast),
-                AstExpression.ComputedField(valueElementName, valueTranslation.Ast)
+                AstExpression.ComputedField("k", keyTranslation.Ast),
+                AstExpression.ComputedField("v", valueTranslation.Ast)
             ]);
 
-            return new TranslatedExpression(expression, ast, serializer);
-        }
-
-        private static IBsonSerializer CreateResultSerializer(
-            Type resultType,
-            IBsonSerializer keySerializer,
-            IBsonSerializer valueSerializer,
-            out string keyElementName,
-            out string valueElementName)
-        {
-            var constructorInfo = resultType.GetConstructor([keySerializer.ValueType, valueSerializer.ValueType]);
-            var classMap = new BsonClassMap(resultType);
-            classMap.MapConstructor(constructorInfo);
-            classMap.AutoMap();
-            var keyMemberMap = classMap.GetMemberMap("Key");
-            keyElementName = keyMemberMap.ElementName;
-            keyMemberMap.SetSerializer(keySerializer);
-            var valueMemberMap = classMap.GetMemberMap("Value");
-            valueElementName = valueMemberMap.ElementName;
-            valueMemberMap.SetSerializer(valueSerializer);
-            classMap.Freeze();
+            var keySerializer = keyTranslation.Serializer;
+            var valueSerializer = valueTranslation.Serializer;
+            var keyValuePairSerializer = KeyValuePairSerializer.Create(BsonType.Document, keySerializer, valueSerializer);
 
-            // have to use BsonClassMapSerializer here to mimic the MemberInitExpressionToAggregationExpressionTranslator to avoid risking a behavioral breaking change
-            var serializerType = typeof(BsonClassMapSerializer<>).MakeGenericType(resultType);
-            return (IBsonSerializer)Activator.CreateInstance(serializerType, classMap);
+            return new TranslatedExpression(expression, ast, keyValuePairSerializer);
         }
     }
 }

tests/MongoDB.Driver.Tests/Linq/Linq3Implementation/Jira/CSharp1326Tests.cs

@@ -49,7 +49,7 @@ public void Projection_of_ArrayOfDocuments_dictionary_keys_and_values_should_wor
                 stages,
                 "{ $match : { ParentId : { $in : [1, 2, 3] }, Gender : 'Male' } }",
                 "{ $group : { _id : '$ParentId', _elements : { $push : '$$ROOT' } } }",
-                "{ $project : { Key : '$_id', Value : '$_elements', _id : 0 } }");
+                "{ $project : { k : '$_id', v : '$_elements', _id : 0 } }");
 
             var results = aggregate.ToList().OrderBy(x => x.Key).ToList();
             results[0].Key.Should().Be(1);

tests/MongoDB.Driver.Tests/Linq/Linq3Implementation/Translators/ExpressionToAggregationExpressionTranslators/NewKeyValuePairExpressionToAggregationExpressionTranslatorTests.cs

@@ -37,7 +37,7 @@ public void NewKeyValuePair_should_translate()
             .Select(d => new KeyValuePair<string,int>("X", d.X));
 
         var stages = Translate(collection, queryable);
-        AssertStages(stages, "{ $project : { Key : 'X', Value : '$X', _id : 0 } }");
+        AssertStages(stages, "{ $project : { k : 'X', v : '$X', _id : 0 } }");
 
         var result = queryable.Single();
         result.Key.Should().Be("X");
@@ -54,7 +54,7 @@ public void KeyValuePair_Create_should_translate()
             .Select(d => KeyValuePair.Create("X", d.X));
 
         var stages = Translate(collection, queryable);
-        AssertStages(stages, "{ $project : { Key : 'X', Value : '$X', _id : 0 } }");
+        AssertStages(stages, "{ $project : { k : 'X', v : '$X', _id : 0 } }");
 
         var result = queryable.Single();
         result.Key.Should().Be("X");