creating anonymous types :)

PoweredSoft.DynamicLinq/Extensions/QueryableExtensions.cs

@@ -69,18 +69,24 @@ namespace PoweredSoft.DynamicLinq
             var ret = qb.Build();
             return ret;
         }
-  
+
         public static IQueryable GroupBy<T>(this IQueryable<T> query, string path)
-            where T : class
-        {
-            var ret = query.GroupBy(typeof(T), path); 
-            return ret as IQueryable;
-        }
+            => QueryableHelpers.GroupBy(query, typeof(T), path);
 
         public static IQueryable GroupBy(this IQueryable query, Type type, string path)
+            => QueryableHelpers.GroupBy(query, type, path);
+
+        public static IQueryable GroupBy<T>(this IQueryable<T> query, Action<GroupBuilder> callback)
+            => query.GroupBy(typeof(T), callback);
+
+        public static IQueryable GroupBy(this IQueryable query, Type type, Action<GroupBuilder> callback)
         {
-            var ret = QueryableHelpers.GroupBy(query, type, path);
-            return ret;
+            var groupBuilder = new GroupBuilder();
+            callback(groupBuilder);
+            if (groupBuilder.Empty)
+                throw new Exception("No group specified, please specify at least one group");
+
+            return QueryableHelpers.GroupBy(query, type, groupBuilder.Parts);
         }
     }
 }

PoweredSoft.DynamicLinq/Fluent/Group/GroupBuilder.cs

@@ -0,0 +1,34 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+using System.Linq;
+
+namespace PoweredSoft.DynamicLinq.Fluent
+{
+    public class GroupBuilder
+    {
+        public List<(string path, string propertyName)> Parts { get; set; } = new List<(string path, string propertyName)>();
+        public bool Empty => !Parts.Any();
+
+        public GroupBuilder Path(string path, string propertyName = null)
+        {
+            if (propertyName == null)
+            {
+                var name = path;
+                if (name.Contains("."))
+                {
+                    var parts = name.Split('.');
+                    name = parts[parts.Length - 1]; // the last one.
+                }
+
+                if (Parts.Any(t => t.propertyName == name))
+                    throw new Exception($"{name} is already taken by another group part, you can specify a property name instead to resolve this issue");
+
+                propertyName = name;
+            }
+
+            Parts.Add((path, propertyName));
+            return this;
+        }
+    }
+}

PoweredSoft.DynamicLinq/Helpers/QueryableHelpers.cs

@@ -6,7 +6,7 @@ using System.Linq.Expressions;
 using System.Reflection;
 using System.Text;
 using System.Threading.Tasks;
-using System.Reflection.Emit;
+
 
 namespace PoweredSoft.DynamicLinq.Helpers
 {
@@ -77,6 +77,28 @@ namespace PoweredSoft.DynamicLinq.Helpers
             return ret;            
         }
 
+        internal static IQueryable GroupBy(IQueryable query, Type type, List<(string path, string propertyName)> parts)
+        {
+            // EXPRESSION
+            var parameter = Expression.Parameter(type, "t");
+            var partExpressions = new List<Expression>();
+
+            var fields = new List<(Type type, string propertyName)>();
+
+            // resolve part expression and create the fields inside the anonymous type.
+            parts.ForEach(part =>
+            {
+                var partExpression = ResolvePathForExpression(parameter, part.path);
+                fields.Add((partExpression.Type, part.propertyName));
+                partExpressions.Add(partExpression);
+            });
+
+            var anonymousType = TypeHelpers.CreateSimpleAnonymousType(fields);
+
+
+            return query;
+        }
+
         public static IQueryable GroupBy(IQueryable query, Type type, string path)
         {
             var parameter = Expression.Parameter(type, "t");
@@ -88,31 +110,6 @@ namespace PoweredSoft.DynamicLinq.Helpers
             return result;
         }
 
-        private static IQueryable GroupByAnonymousObject(IQueryable query, Type type, ParameterExpression parameter, List<Expression> fields) 
-        {
-            throw new NotSupportedException();
-            /*
-            var dynamicAssemblyName = new AssemblyName("PoweredSoft.DynamicLinq.DynamicTypes");
-            var dynamicAssembly = AssemblyBuilder.DefineDynamicAssembly(dynamicAssemblyName, System.Reflection.Emit.AssemblyBuilderAccess.Run);
-            System.Reflection.Emit.ModuleBuilder dynamicModule = dynamicAssembly.DefineDynamicModule("TempAssembly");
-
-            TypeBuilder dynamicAnonymousType = dynamicModule.DefineType("AnonymousType", TypeAttributes.Public);
-
-            int i = 0;
-            fields.ForEach(field =>
-            {
-                var fieldName = $"A_{++i}"; // tODO
-                dynamicAnonymousType.DefineField(fieldName.
-            });
-
-            dynamicAnonymousType.DefineField(, typeof(TFieldA), FieldAttributes.Public);
-            dynamicAnonymousType.DefineField(fieldNameB, typeof(TFieldB), FieldAttributes.Public);
-
-            return dynamicAnonymousType.CreateType();
-
-            throw new NotImplementedException();   */
-        }
-
         /// <summary>
         /// Returns the right expression for a path supplied.
         /// </summary>

PoweredSoft.DynamicLinq/Helpers/TypeHelpers.cs

@@ -3,11 +3,17 @@ using System.Collections.Generic;
 using System.Linq;
 using System.Text;
 using System.Threading.Tasks;
+using System.Reflection.Emit;
+using System.Reflection;
 
 namespace PoweredSoft.DynamicLinq.Helpers
 {
     public static class TypeHelpers
     {
+        internal static Lazy<AssemblyName> DynamicAssemblyName = new Lazy<AssemblyName>(() => new AssemblyName("PoweredSoft.DynamicLinq.DynamicTypes"));
+        internal static Lazy<AssemblyBuilder> DynamicAssembly = new Lazy<AssemblyBuilder>(() => AssemblyBuilder.DefineDynamicAssembly(DynamicAssemblyName.Value, AssemblyBuilderAccess.Run));
+        internal static Lazy<ModuleBuilder> DynamicModule = new Lazy<ModuleBuilder>(() => DynamicAssembly.Value.DefineDynamicModule("PoweredSoft.DynamicLinq.DynamicTypes"));
+
         public static object ConvertFrom(Type type, object source)
         {
             object ret = null;
@@ -28,5 +34,45 @@ namespace PoweredSoft.DynamicLinq.Helpers
             ret = Convert.ChangeType(source, notNullableType);
             return ret;
         }
+
+        internal static TypeInfo CreateSimpleAnonymousType(List<(Type type, string name)> fields)
+        {
+            // DYNAMIC TYPE CREATION
+            var typeName = $"PSDLProxy_{Guid.NewGuid().ToString("N")}";
+            var dynamicType = DynamicModule.Value.DefineType(typeName, TypeAttributes.Class | TypeAttributes.Public);
+            fields.ForEach(field =>
+            {
+                CreatePropertyOnType(dynamicType, field.name, field.type);
+            });
+            var ret = dynamicType.CreateTypeInfo();
+            return ret;
+        }
+
+        internal static void CreatePropertyOnType(TypeBuilder typeBuilder, string propertyName, Type propertyType)
+        {
+            // Generate a property called "Name"
+            var field = typeBuilder.DefineField("_" + propertyName, propertyType, FieldAttributes.Private);
+            var attributes = MethodAttributes.Public | MethodAttributes.SpecialName | MethodAttributes.HideBySig;
+
+            // generate property
+            var propertyBuilder = typeBuilder.DefineProperty(propertyName, PropertyAttributes.HasDefault, propertyType, null);
+
+            // Generate getter method
+            var getter = typeBuilder.DefineMethod("get_" + propertyName, attributes, propertyType, Type.EmptyTypes);
+            var il = getter.GetILGenerator();
+            il.Emit(OpCodes.Ldarg_0);        // Push "this" on the stack
+            il.Emit(OpCodes.Ldfld, field);   // Load the field "_Name"
+            il.Emit(OpCodes.Ret);            // Return
+            propertyBuilder.SetGetMethod(getter);
+
+            // Generate setter method
+            var setter = typeBuilder.DefineMethod("set_" + propertyName, attributes, null, new[] { propertyType });
+            il = setter.GetILGenerator();
+            il.Emit(OpCodes.Ldarg_0);        // Push "this" on the stack
+            il.Emit(OpCodes.Ldarg_1);        // Push "value" on the stack
+            il.Emit(OpCodes.Stfld, field);   // Set the field "_Name" to "value"
+            il.Emit(OpCodes.Ret);            // Return
+            propertyBuilder.SetSetMethod(setter);
+        }
     }
 }

PoweredSoft.DynamicLinq/PoweredSoft.DynamicLinq.csproj

@@ -21,4 +21,8 @@
     <Folder Include="Properties\" />
   </ItemGroup>
 
+  <ItemGroup>
+    <PackageReference Include="System.Reflection.Emit" Version="4.3.0" />
+  </ItemGroup>
+
 </Project>