Let clause : explicitly generate just the properties we need

src/AutoMapper/Execution/ProxyGenerator.cs

@@ -51,12 +51,11 @@ private static Type EmitProxy(TypeDescription typeDescription)
             var interfaceType = typeDescription.Type;
             var additionalProperties = typeDescription.AdditionalProperties;
             var propertyNames = string.Join("_", additionalProperties.Select(p => p.Name));
-            string name =
-                $"Proxy{propertyNames}<{Regex.Replace(interfaceType.AssemblyQualifiedName ?? interfaceType.FullName ?? interfaceType.Name, @"[\s,]+", "_")}>";
+            var typeName = $"Proxy_{interfaceType.FullName}_{propertyNames}_{typeDescription.GetHashCode()}";
             var allInterfaces = new List<Type> { interfaceType };
             allInterfaces.AddRange(interfaceType.GetTypeInfo().ImplementedInterfaces);
-            Debug.WriteLine(name, "Emitting proxy type");
-            TypeBuilder typeBuilder = proxyModule.DefineType(name,
+            Debug.WriteLine(typeName, "Emitting proxy type");
+            TypeBuilder typeBuilder = proxyModule.DefineType(typeName,
                 TypeAttributes.Class | TypeAttributes.Sealed | TypeAttributes.Public, typeof(ProxyBase),
                 interfaceType.IsInterface() ? new[] { interfaceType } : new Type[0]);
             ConstructorBuilder constructorBuilder = typeBuilder.DefineConstructor(MethodAttributes.Public,
@@ -176,7 +175,11 @@ public TypeDescription(Type type) : this(type, PropertyDescription.Empty)
         public TypeDescription(Type type, IEnumerable<PropertyDescription> additionalProperties)
         {
             Type = type ?? throw new ArgumentNullException(nameof(type));
-            AdditionalProperties = additionalProperties?.ToArray() ?? throw new ArgumentNullException(nameof(additionalProperties));
+            if(additionalProperties == null)
+            {
+                throw new ArgumentNullException(nameof(additionalProperties));
+            }
+            AdditionalProperties = additionalProperties.OrderBy(p => p.Name).ToArray();
         }
 
         public Type Type { get; }

src/AutoMapper/QueryableExtensions/ExpressionBuilder.cs

@@ -504,14 +504,14 @@ public override QueryExpressions GetSubQueryExpression(ExpressionBuilder builder
                     MapFromSource = path.PropertyMaps.Take(path.PropertyMaps.Length - 1).Select(pm=>pm.SourceMember).MemberAccesses(instanceParameter),
                     Property = new PropertyDescription
                     (
-                        string.Join("_", path.PropertyMaps.Select(pm => pm.DestinationProperty.Name)),
+                        string.Join("#", path.PropertyMaps.Select(pm => pm.DestinationProperty.Name)),
                         path.Last.SourceType
                     ),
                     Marker = path.Marker
                 }).ToArray();
 
-                var letProperties = letMapInfos.Select(m => m.Property);
-                var letType = ProxyGenerator.GetSimilarType(request.SourceType, letProperties);
+                var properties = letMapInfos.Select(m => m.Property).Concat(GetMemberAccessesVisitor.Retrieve(projection, instanceParameter));
+                var letType = ProxyGenerator.GetSimilarType(typeof(object), properties);
                 var typeMapFactory = new TypeMapFactory();
                 TypeMap firstTypeMap;
                 lock(_configurationProvider)
@@ -539,9 +539,37 @@ void ReplaceSubQueries()
                 }
             }
 
+            class GetMemberAccessesVisitor : ExpressionVisitor
+            {
+                private readonly Expression _target;
+
+                public List<MemberInfo> Members { get; } = new List<MemberInfo>();
+
+                public GetMemberAccessesVisitor(Expression target)
+                {
+                    _target = target;
+                }
+
+                protected override Expression VisitMember(MemberExpression node)
+                {
+                    if(node.Expression == _target)
+                    {
+                        Members.Add(node.Member);
+                    }
+                    return base.VisitMember(node);
+                }
+
+                public static IEnumerable<PropertyDescription> Retrieve(Expression expression, Expression target)
+                {
+                    var visitor = new GetMemberAccessesVisitor(target);
+                    visitor.Visit(expression);
+                    return visitor.Members.Select(member => new PropertyDescription(member.Name, member.GetMemberType()));
+                }
+            }
+
             class ReplaceMemberAccessesVisitor : ExpressionVisitor
             {
-                Expression _oldObject, _newObject;
+                private readonly Expression _oldObject, _newObject;
 
                 public ReplaceMemberAccessesVisitor(Expression oldObject, Expression newObject)
                 {

src/IntegrationTests/CustomMapFrom/MapObjectPropertyFromSubQuery.cs

@@ -8,6 +8,7 @@
 
 namespace AutoMapper.IntegrationTests
 {
+    using System.ComponentModel.DataAnnotations.Schema;
     using System.Linq.Expressions;
     using QueryableExtensions;
 
@@ -162,6 +163,8 @@ public partial class Product
             public bool ECommercePublished { get; set; }
             public virtual ICollection<Article> Articles { get; set; }
             public int Value { get; }
+            [NotMapped]
+            public int NotMappedValue { get; set; }
             public virtual List<Article> OtherArticles { get; }
         }