Add OnlyOnInclude option for the root rewritter

samples/BasicSample/Program.cs

@@ -21,7 +21,7 @@ namespace BasicSample
         public string FullName { get; set; }
         private string _FullName => FirstName + " " + LastName;
 
-        [Projectable(UseMemberBody = nameof(_TotalSpent))]
+        [Projectable(UseMemberBody = nameof(_TotalSpent), OnlyOnInclude = true)]
         public double TotalSpent { get; set; }
         private double _TotalSpent => Orders.Sum(x => x.PriceSum);
 
@@ -154,10 +154,11 @@ namespace BasicSample
             }
 
             {
-                var result = dbContext.Users.FirstOrDefault();
+                Console.WriteLine($"Unloaded total: {dbContext.Users.First().TotalSpent}");
+                var result = dbContext.Users.Include(x => x.TotalSpent).FirstOrDefault();
                 Console.WriteLine($"Our first user {result.FullName} has spent {result.TotalSpent}");
                 
-                result = dbContext.Users.FirstOrDefault(x => x.TotalSpent > 1);
+                result = dbContext.Users.Include(x => x.TotalSpent).FirstOrDefault(x => x.TotalSpent > 1);
                 Console.WriteLine($"Our first user {result.FullName} has spent {result.TotalSpent}");
                 
                 var spent = dbContext.Users.Sum(x => x.TotalSpent);

src/EntityFrameworkCore.Projectables.Abstractions/ProjectableAttribute.cs

@@ -1,8 +1,4 @@
 using System;
-using System.Collections.Generic;
-using System.Linq;
-using System.Text;
-using System.Threading.Tasks;
 
 namespace EntityFrameworkCore.Projectables
 {
@@ -23,5 +19,12 @@ namespace EntityFrameworkCore.Projectables
         /// or null to get it from the current member.
         /// </summary>
         public string? UseMemberBody { get; set; }
+
+        /// <summary>
+        /// <c>true</c> will allow you to request for this property by
+        /// explicitly calling .Include(x => x.Property) on the query,
+        /// <c>false</c> will always consider this query to be included.
+        /// </summary>
+        public bool OnlyOnInclude { get; set; }
     }
 }

src/EntityFrameworkCore.Projectables/Services/ProjectableExpressionReplacer.cs

@@ -5,6 +5,7 @@ using System.Linq;
 using System.Linq.Expressions;
 using System.Reflection;
 using EntityFrameworkCore.Projectables.Extensions;
+using Microsoft.EntityFrameworkCore;
 using Microsoft.EntityFrameworkCore.Metadata;
 using Microsoft.EntityFrameworkCore.Query;
 
@@ -16,6 +17,7 @@ namespace EntityFrameworkCore.Projectables.Services
         readonly ExpressionArgumentReplacer _expressionArgumentReplacer = new();
         readonly Dictionary<MemberInfo, LambdaExpression?> _projectableMemberCache = new();
         private bool _disableRootRewrite;
+        private List<string> _includedProjections = new();
         private IEntityType? _entityType;
 
         private readonly MethodInfo _select;
@@ -60,6 +62,7 @@ namespace EntityFrameworkCore.Projectables.Services
         public Expression? Replace(Expression? node)
         {
             _disableRootRewrite = false;
+            _includedProjections.Clear();
             var ret = Visit(node);
 
             if (_disableRootRewrite)
@@ -138,6 +141,28 @@ namespace EntityFrameworkCore.Projectables.Services
 
         protected override Expression VisitMethodCall(MethodCallExpression node)
         {
+            if (node.Method.Name == nameof(EntityFrameworkQueryableExtensions.Include))
+            {
+                var include = node.Arguments[1] switch {
+                    ConstantExpression { Value: string str } => str,
+                    LambdaExpression { Body: MemberExpression member } => member.Member.Name,
+                    UnaryExpression { Operand: LambdaExpression { Body: MemberExpression member } } => member.Member.Name,
+                    _ => null
+                };
+                // Only rewrite the include if it includes a projectable property (or if we don't know what's happening).
+                var ret = Visit(node.Arguments[0]);
+                // The visit here is needed because we need the _entityType defined on the query root for the condition below.
+                if (
+                    include != null
+                    && _entityType?.ClrType
+                        ?.GetProperty(include)
+                        ?.GetCustomAttribute<ProjectableAttribute>() != null)
+                {
+                    _includedProjections.Add(include);
+                    return ret;
+                }
+            }
+
             // Replace MethodGroup arguments with their reflected expressions.
             // Note that MethodCallExpression.Update returns the original Expression if argument values have not changed.
             node = node.Update(node.Object, node.Arguments.Select(arg => arg switch {
@@ -212,13 +237,13 @@ namespace EntityFrameworkCore.Projectables.Services
                     var updatedBody = _expressionArgumentReplacer.Visit(reflectedExpression.Body);
                     _expressionArgumentReplacer.ParameterArgumentMapping.Clear();
 
-                    return base.Visit(
+                    return Visit(
                         updatedBody
                     );
                 }
                 else
                 {
-                    return base.Visit(
+                    return Visit(
                         reflectedExpression.Body
                     );
                 }
@@ -243,7 +268,14 @@ namespace EntityFrameworkCore.Projectables.Services
         private Expression _AddProjectableSelect(Expression node, IEntityType entityType)
         {
             var projectableProperties = entityType.ClrType.GetProperties()
-                .Where(x => x.IsDefined(typeof(ProjectableAttribute), false))
+                .Where(x => {
+                    var attr = x.GetCustomAttribute<ProjectableAttribute>();
+                    if (attr == null)
+                        return false;
+                    if (attr.OnlyOnInclude)
+                        return _includedProjections.Contains(x.Name);
+                    return true;
+                })
                 .Where(x => x.CanWrite)
                 .ToList();
 
@@ -291,7 +323,7 @@ namespace EntityFrameworkCore.Projectables.Services
             _expressionArgumentReplacer.ParameterArgumentMapping.Add(lambda.Parameters[0], para);
             var updatedBody = _expressionArgumentReplacer.Visit(lambda.Body);
             _expressionArgumentReplacer.ParameterArgumentMapping.Clear();
-            return base.Visit(updatedBody);
+            return Visit(updatedBody);
         }
     }
 }