Query: Add optimization to conditional being equated to equality

Resolves #12148

src/EFCore/Query/Internal/NullCheckRemovingExpressionVisitor.cs

@@ -18,6 +18,19 @@ public class NullCheckRemovingExpressionVisitor : ExpressionVisitor
         private readonly NullSafeAccessVerifyingExpressionVisitor _nullSafeAccessVerifyingExpressionVisitor
             = new NullSafeAccessVerifyingExpressionVisitor();
 
+        /// <summary>
+        ///     This is an internal API that supports the Entity Framework Core infrastructure and not subject to
+        ///     the same compatibility standards as public APIs. It may be changed or removed without notice in
+        ///     any release. You should only use it directly in your code with extreme caution and knowing that
+        ///     doing so can result in application failures when updating to a new Entity Framework Core release.
+        /// </summary>
+        protected override Expression VisitBinary(BinaryExpression binaryExpression)
+        {
+            var visitedExpression = base.VisitBinary(binaryExpression);
+
+            return TryOptimizeConditionalEquality(visitedExpression) ?? visitedExpression;
+        }
+
         /// <summary>
         ///     This is an internal API that supports the Entity Framework Core infrastructure and not subject to
         ///     the same compatibility standards as public APIs. It may be changed or removed without notice in
@@ -60,6 +73,42 @@ protected override Expression VisitConditional(ConditionalExpression conditional
             return base.VisitConditional(conditionalExpression);
         }
 
+        private Expression TryOptimizeConditionalEquality(Expression expression)
+        {
+            // Simplify (a ? b : null) == null => a
+            // Simplify (a ? null : c) == null => !a
+            if (expression is BinaryExpression binaryExpression
+                && binaryExpression.NodeType == ExpressionType.Equal
+                && (binaryExpression.Left is ConditionalExpression
+                    || binaryExpression.Right is ConditionalExpression))
+            {
+                Expression comparedExpression;
+                if (binaryExpression.Left is ConditionalExpression conditionalExpression)
+                {
+                    comparedExpression = binaryExpression.Right;
+                }
+                else
+                {
+                    conditionalExpression = binaryExpression.Right as ConditionalExpression;
+                    comparedExpression = binaryExpression.Left;
+                }
+
+                if (conditionalExpression.IfTrue.IsNullConstantExpression()
+                    && comparedExpression.IsNullConstantExpression())
+                {
+                    return conditionalExpression.Test;
+                }
+
+                if (conditionalExpression.IfFalse.IsNullConstantExpression()
+                    && comparedExpression.IsNullConstantExpression())
+                {
+                    return Expression.Not(conditionalExpression.Test);
+                }
+            }
+
+            return null;
+        }
+
         private sealed class NullSafeAccessVerifyingExpressionVisitor : ExpressionVisitor
         {
             private readonly ISet<Expression> _nullSafeAccesses = new HashSet<Expression>(ExpressionEqualityComparer.Instance);

test/EFCore.Cosmos.FunctionalTests/Query/NorthwindMiscellaneousQueryCosmosTest.cs

@@ -4178,6 +4178,12 @@ public override Task DefaultIfEmpty_Sum_over_collection_navigation(bool async)
             return base.DefaultIfEmpty_Sum_over_collection_navigation(async);
         }
 
+        [ConditionalTheory(Skip = "Non embedded collection subquery Issue#17246")]
+        public override Task Entity_equality_on_subquery_with_null_check(bool async)
+        {
+            return base.Entity_equality_on_subquery_with_null_check(async);
+        }
+
         private void AssertSql(params string[] expected)
             => Fixture.TestSqlLoggerFactory.AssertBaseline(expected);
 

test/EFCore.InMemory.FunctionalTests/Query/GearsOfWarQueryInMemoryTest.cs

@@ -27,10 +27,6 @@ public override Task Client_side_equality_with_parameter_works_with_optional_nav
         public override Task Where_coalesce_with_anonymous_types(bool async)
             => base.Where_coalesce_with_anonymous_types(async);
 
-        [ConditionalTheory(Skip = "issue #17386")]
-        public override Task Where_conditional_with_anonymous_type(bool async)
-            => base.Where_conditional_with_anonymous_type(async);
-
         [ConditionalTheory(Skip = "issue #17386")]
         public override Task GetValueOrDefault_on_DateTimeOffset(bool async)
             => base.GetValueOrDefault_on_DateTimeOffset(async);

test/EFCore.Specification.Tests/Query/GearsOfWarQueryTestBase.cs

@@ -1192,17 +1192,16 @@ orderby g.Nickname
         [MemberData(nameof(IsAsyncData))]
         public virtual Task Where_conditional_with_anonymous_type(bool async)
         {
-            return AssertTranslationFailed(
-                () => AssertQuery(
-                    async,
-                    ss => from g in ss.Set<Gear>()
-                          orderby g.Nickname
-                          where (g.LeaderNickname != null
-                                  ? new { g.HasSoulPatch }
-                                  : null)
-                              == null
-                          select g.Nickname,
-                    assertOrder: true));
+            return AssertQuery(
+                async,
+                ss => from g in ss.Set<Gear>()
+                        orderby g.Nickname
+                        where (g.LeaderNickname != null
+                                ? new { g.HasSoulPatch }
+                                : null)
+                            == null
+                        select g.Nickname,
+                assertOrder: true);
         }
 
         [ConditionalTheory]

test/EFCore.Specification.Tests/Query/NorthwindMiscellaneousQueryTestBase.cs

@@ -794,7 +794,8 @@ public virtual Task Ternary_should_not_evaluate_both_sides_with_parameter(bool a
                     o => new
                     {
                         // ReSharper disable SimplifyConditionalTernaryExpression
-                        Data1 = param != null ? o.OrderDate == param.Value : true, Data2 = param == null ? true : o.OrderDate == param.Value
+                        Data1 = param != null ? o.OrderDate == param.Value : true,
+                        Data2 = param == null ? true : o.OrderDate == param.Value
                         // ReSharper restore SimplifyConditionalTernaryExpression
                     }));
         }
@@ -3441,7 +3442,7 @@ public virtual void Select_Where_Subquery_Equality()
             using var context = CreateContext();
             var orders
                 = (from o in context.Orders.OrderBy(o => o.OrderID).Take(1)
-                   // ReSharper disable once UseMethodAny.0
+                       // ReSharper disable once UseMethodAny.0
                    where (from od in context.OrderDetails.OrderBy(od => od.OrderID).Take(2)
                           where (from c in context.Set<Customer>()
                                  where c.CustomerID == o.CustomerID
@@ -6241,5 +6242,23 @@ public virtual Task DefaultIfEmpty_Sum_over_collection_navigation(bool async)
                     .Select(c => new { c.CustomerID, Sum = c.Orders.Select(o => o.OrderID).DefaultIfEmpty().Sum() }),
                 elementSorter: c => c.CustomerID);
         }
+
+        [ConditionalTheory]
+        [MemberData(nameof(IsAsyncData))]
+        public virtual Task Entity_equality_on_subquery_with_null_check(bool async)
+        {
+            return AssertQuery(
+                async,
+                ss => ss.Set<Customer>()
+                    .Select(c => new
+                    {
+                        c.CustomerID,
+                        Order = (c.Orders.Any() ? c.Orders.FirstOrDefault() : null) == null
+                            ? null
+                            : new { c.Orders.FirstOrDefault().OrderDate }
+                    }),
+                elementSorter: c => c.CustomerID,
+                elementAsserter: (e, a) => AssertEqual(e.Order, a.Order));
+        }
     }
 }

test/EFCore.SqlServer.FunctionalTests/Query/GearsOfWarQuerySqlServerTest.cs

@@ -1119,6 +1119,17 @@ FROM [Gears] AS [g]
 ORDER BY [g].[Nickname]");
         }
 
+        public override async Task Where_conditional_with_anonymous_type(bool async)
+        {
+            await base.Where_conditional_with_anonymous_type(async);
+
+            AssertSql(
+                @"SELECT [g].[Nickname]
+FROM [Gears] AS [g]
+WHERE [g].[LeaderNickname] IS NULL
+ORDER BY [g].[Nickname]");
+        }
+
         public override async Task Select_coalesce_with_anonymous_types(bool async)
         {
             await base.Select_coalesce_with_anonymous_types(async);

test/EFCore.SqlServer.FunctionalTests/Query/NorthwindMiscellaneousQuerySqlServerTest.cs

@@ -5202,6 +5202,24 @@ FROM [Orders] AS [o]
 FROM [Customers] AS [c]");
         }
 
+        public override async Task Entity_equality_on_subquery_with_null_check(bool async)
+        {
+            await base.Entity_equality_on_subquery_with_null_check(async);
+
+            AssertSql(
+                @"SELECT [c].[CustomerID], CASE
+    WHEN NOT (EXISTS (
+        SELECT 1
+        FROM [Orders] AS [o]
+        WHERE [c].[CustomerID] = [o].[CustomerID])) THEN CAST(1 AS bit)
+    ELSE CAST(0 AS bit)
+END, (
+    SELECT TOP(1) [o0].[OrderDate]
+    FROM [Orders] AS [o0]
+    WHERE [c].[CustomerID] = [o0].[CustomerID])
+FROM [Customers] AS [c]");
+        }
+
         private void AssertSql(params string[] expected)
             => Fixture.TestSqlLoggerFactory.AssertBaseline(expected);
 

test/EFCore.SqlServer.FunctionalTests/Query/TPTGearsOfWarQuerySqlServerTest.cs

@@ -1363,6 +1363,17 @@ FROM [Gears] AS [g]
 ORDER BY [g].[Nickname]");
         }
 
+        public override async Task Where_conditional_with_anonymous_type(bool async)
+        {
+            await base.Where_conditional_with_anonymous_type(async);
+
+            AssertSql(
+                @"SELECT [g].[Nickname]
+FROM [Gears] AS [g]
+WHERE [g].[LeaderNickname] IS NULL
+ORDER BY [g].[Nickname]");
+        }
+
         public override async Task Select_coalesce_with_anonymous_types(bool async)
         {
             await base.Select_coalesce_with_anonymous_types(async);