Fix to #5454 - Error when using Where with reference

Problem was for happening for queries with optional navigations like so:

context.Orders.Where(o => o.Customer.IsVip)

In this case Customer can be nullable, so IsVip can also be nullable. We compensate for this by introducing the following:

context.Orders.Where(o => o.Customer != null ? (bool?)o.Customer.IsVip : (bool?)null)

However, we didn't convert it back to the original type (users had to introduce those casts themselves). Without the cast, those queries were throwing compile-time exceptions that were not very informative.

Fix is to cast back to the original type requested by user:

context.Orders.Where(o => (bool)(o.Customer != null ? (bool?)o.Customer.IsVip : (bool?)null))

This still may cause runtime errors if o.Customer is actually null, but those are much more understandable now.

Also fixed compilation errors for complex Skip/Take arguments. Those are evaluated on the client for the time being.

src/Microsoft.EntityFrameworkCore.Relational/Query/Internal/RelationalResultOperatorHandler.cs

@@ -650,9 +650,22 @@ private static Expression HandleSkip(HandlerContext handlerContext)
         {
             var skipResultOperator = (SkipResultOperator)handlerContext.ResultOperator;
 
-            handlerContext.SelectExpression.Offset = skipResultOperator.Count;
+            var sqlTranslatingExpressionVisitor
+                = handlerContext.SqlTranslatingExpressionVisitorFactory
+                    .Create(
+                        handlerContext.QueryModelVisitor,
+                        handlerContext.SelectExpression,
+                        bindParentQueries: true);
 
-            return handlerContext.EvalOnServer;
+            var offset = sqlTranslatingExpressionVisitor.Visit(skipResultOperator.Count);
+            if (offset != null)
+            {
+                handlerContext.SelectExpression.Offset = offset;
+
+                return handlerContext.EvalOnServer;
+            }
+
+            return handlerContext.EvalOnClient();
         }
 
         private static Expression HandleSum(HandlerContext handlerContext)
@@ -676,9 +689,22 @@ private static Expression HandleTake(HandlerContext handlerContext)
         {
             var takeResultOperator = (TakeResultOperator)handlerContext.ResultOperator;
 
-            handlerContext.SelectExpression.Limit = takeResultOperator.Count;
+            var sqlTranslatingExpressionVisitor
+                = handlerContext.SqlTranslatingExpressionVisitorFactory
+                    .Create(
+                        handlerContext.QueryModelVisitor,
+                        handlerContext.SelectExpression,
+                        bindParentQueries: true);
 
-            return handlerContext.EvalOnServer;
+            var limit = sqlTranslatingExpressionVisitor.Visit(takeResultOperator.Count);
+            if (limit != null)
+            {
+                handlerContext.SelectExpression.Limit = takeResultOperator.Count;
+
+                return handlerContext.EvalOnServer;
+            }
+
+            return handlerContext.EvalOnClient();
         }
 
         private static void SetProjectionConditionalExpression(

src/Microsoft.EntityFrameworkCore.Specification.Tests/GearsOfWarQueryTestBase.cs

@@ -1500,6 +1500,125 @@ public virtual void Coalesce_operator_in_projection_with_other_conditions()
             }
         }
 
+        [ConditionalFact]
+        public virtual void Optional_navigation_type_compensation_works_with_predicate()
+        {
+            using (var context = CreateContext())
+            {
+                var query = context.Tags.Where(t => t.Note != "K.I.A." && t.Gear.HasSoulPatch);
+                var result = query.ToList();
+
+                Assert.Equal(2, result.Count);
+            }
+        }
+
+        [ConditionalFact]
+        public virtual void Optional_navigation_type_compensation_works_with_projection()
+        {
+            using (var context = CreateContext())
+            {
+                var query = context.Tags.Where(t => t.Note != "K.I.A.").Select(t => t.Gear.SquadId);
+                var result = query.ToList();
+
+                Assert.Equal(5, result.Count);
+            }
+        }
+
+        [ConditionalFact]
+        public virtual void Optional_navigation_type_compensation_works_with_projection_into_anonymous_type()
+        {
+            using (var context = CreateContext())
+            {
+                var query = context.Tags.Where(t => t.Note != "K.I.A.").Select(t => new { t.Gear.SquadId });
+                var result = query.ToList();
+
+                Assert.Equal(5, result.Count);
+            }
+        }
+
+        [ConditionalFact]
+        public virtual void Optional_navigation_type_compensation_works_with_orderby()
+        {
+            using (var context = CreateContext())
+            {
+                var query = context.Tags.Where(t => t.Note != "K.I.A.").OrderBy(t => t.Gear.SquadId);
+                var result = query.ToList();
+
+                Assert.Equal(5, result.Count);
+            }
+        }
+
+        [ConditionalFact]
+        public virtual void Optional_navigation_type_compensation_works_with_groupby()
+        {
+            using (var context = CreateContext())
+            {
+                var query = context.Tags.Where(t => t.Note != "K.I.A.").GroupBy(t => t.Gear.SquadId);
+                var result = query.ToList();
+
+                Assert.Equal(2, result.Count);
+            }
+        }
+
+        [ConditionalFact]
+        public virtual void Optional_navigation_type_compensation_works_with_all()
+        {
+            using (var context = CreateContext())
+            {
+                var query = context.Tags.Where(t => t.Note != "K.I.A.").All(t => t.Gear.HasSoulPatch);
+
+                Assert.False(query);
+            }
+        }
+
+        [ConditionalFact]
+        public virtual void Optional_navigation_type_compensation_works_with_contains()
+        {
+            using (var context = CreateContext())
+            {
+                var query = context.Tags.Where(t => t.Note != "K.I.A." && context.Gears.Select(g => g.SquadId).Contains(t.Gear.SquadId));
+                var result = query.ToList();
+
+                Assert.Equal(5, result.Count);
+            }
+        }
+
+        [ConditionalFact]
+        public virtual void Optional_navigation_type_compensation_works_with_skip()
+        {
+            using (var context = CreateContext())
+            {
+                var query = context.Tags.Where(t => t.Note != "K.I.A.").Select(t => context.Gears.Skip(t.Gear.SquadId));
+                var result = query.ToList();
+
+                Assert.Equal(5, result.Count);
+            }
+        }
+
+        [ConditionalFact]
+        public virtual void Optional_navigation_type_compensation_works_with_take()
+        {
+            using (var context = CreateContext())
+            {
+                var query = context.Tags.Where(t => t.Note != "K.I.A.").Select(t => context.Gears.Take(t.Gear.SquadId));
+                var result = query.ToList();
+
+                Assert.Equal(5, result.Count);
+            }
+        }
+
+        [ConditionalFact]
+        public virtual void Optional_navigation_type_compensation_throws_rasonable_exception_for_nullable_values()
+        {
+            using (var context = CreateContext())
+            {
+                var query = context.Tags.Where(t => t.Gear.HasSoulPatch);
+
+                //Nullable object must have a value
+                Assert.Throws<InvalidOperationException>(() => query.ToList());
+            }
+        }
+
         protected GearsOfWarContext CreateContext() => Fixture.CreateContext(TestStore);
 
         protected GearsOfWarQueryTestBase(TFixture fixture)

src/Microsoft.EntityFrameworkCore.Specification.Tests/TestModels/GearsOfWarModel/Gear.cs

@@ -36,6 +36,8 @@ public Gear()
         public string LeaderNickname { get; set; }
         public int LeaderSquadId { get; set; }
 
+        public bool HasSoulPatch { get; set; }
+
         [NotMapped]
         public bool IsMarcus => Nickname == "Marcus";
     }

src/Microsoft.EntityFrameworkCore.Specification.Tests/TestModels/GearsOfWarModel/GearsOfWarModelInitializer.cs

@@ -189,6 +189,7 @@ public static void Seed(GearsOfWarContext context)
             {
                 Nickname = "Dom",
                 FullName = "Dominic Santiago",
+                HasSoulPatch = false,
                 SquadId = deltaSquad.Id,
                 Rank = MilitaryRank.Corporal,
                 AssignedCity = ephyra,
@@ -201,6 +202,7 @@ public static void Seed(GearsOfWarContext context)
             {
                 Nickname = "Cole Train",
                 FullName = "Augustus Cole",
+                HasSoulPatch = false,
                 SquadId = deltaSquad.Id,
                 Rank = MilitaryRank.Private,
                 CityOrBirthName = hanover.Name,
@@ -213,6 +215,7 @@ public static void Seed(GearsOfWarContext context)
             {
                 Nickname = "Paduk",
                 FullName = "Garron Paduk",
+                HasSoulPatch = false,
                 SquadId = kiloSquad.Id,
                 Rank = MilitaryRank.Private,
                 CityOrBirthName = unknown.Name,
@@ -224,6 +227,7 @@ public static void Seed(GearsOfWarContext context)
             {
                 Nickname = "Baird",
                 FullName = "Damon Baird",
+                HasSoulPatch = true,
                 SquadId = deltaSquad.Id,
                 Rank = MilitaryRank.Corporal,
                 CityOrBirthName = unknown.Name,
@@ -237,6 +241,7 @@ public static void Seed(GearsOfWarContext context)
             {
                 Nickname = "Marcus",
                 FullName = "Marcus Fenix",
+                HasSoulPatch = true,
                 SquadId = deltaSquad.Id,
                 Rank = MilitaryRank.Sergeant,
                 CityOrBirthName = jacinto.Name,