Fixes #20604 - Treat ToString as casting to string in the database

src/EFCore.SqlServer/Query/Internal/SqlServerObjectToStringTranslator.cs

@@ -101,6 +101,11 @@ public SqlServerObjectToStringTranslator(ISqlExpressionFactory sqlExpressionFact
                 _sqlExpressionFactory.Constant(true.ToString()));
         }
 
+        if (instance.Type.IsEnum)
+        {
+            return _sqlExpressionFactory.Convert(instance, typeof(string));
+        }
+
         return TypeMapping.TryGetValue(instance.Type, out var storeType)
             ? _sqlExpressionFactory.Function(
                 "CONVERT",

src/EFCore.Sqlite.Core/Query/Internal/SqliteObjectToStringTranslator.cs

@@ -98,7 +98,7 @@ public SqliteObjectToStringTranslator(ISqlExpressionFactory sqlExpressionFactory
                 _sqlExpressionFactory.Constant(true.ToString()));
         }
 
-        return TypeMapping.Contains(instance.Type)
+        return TypeMapping.Contains(instance.Type) || instance.Type.IsEnum
             ? _sqlExpressionFactory.Convert(instance, typeof(string))
             : null;
     }

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

@@ -139,4 +139,20 @@ public override Task Where_compare_anonymous_types(bool async)
 
     public override Task Subquery_inside_Take_argument(bool async)
         => Task.CompletedTask;
+
+    public override Task ToString_nullable_enum_property_projection(bool async)
+        => AssertQuery(
+            async,
+            ss => ss.Set<Weapon>().Select(w => w.AmmunitionType.ToString()),
+            ss => ss.Set<Weapon>().Select(w => w.AmmunitionType != null ? w.AmmunitionType.ToString() : null));
+
+    public override Task ToString_nullable_enum_contains(bool async)
+        => AssertQuery(
+            async,
+            ss => ss.Set<Weapon>().Where(w => w.AmmunitionType.ToString().Contains("Cart")).Select(g => g.Name));
+
+    public override Task ToString_enum_property_projection(bool async)
+        => AssertQuery(
+            async,
+            ss => ss.Set<Gear>().Select(g => g.Rank.ToString()));
 }

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

@@ -337,7 +337,12 @@ protected override void OnModelCreating(ModelBuilder modelBuilder, DbContext con
                 b.HasOne(w => w.Owner).WithMany(g => g.Weapons).HasForeignKey(w => w.OwnerFullName).HasPrincipalKey(g => g.FullName);
             });
 
-        modelBuilder.Entity<Mission>().Property(m => m.Id).ValueGeneratedNever();
+        modelBuilder.Entity<Mission>(
+            b =>
+            {
+                b.Property(m => m.Id).ValueGeneratedNever();
+                b.Property(m => m.Difficulty).HasConversion<string>();
+            });
 
         modelBuilder.Entity<SquadMission>(
             b =>

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

@@ -89,6 +89,37 @@ public virtual Task ToString_boolean_property_nullable(bool async)
             async,
             ss => ss.Set<LocustHorde>().Select(lh => lh.Eradicated.ToString()));
 
+    [ConditionalTheory]
+    [MemberData(nameof(IsAsyncData))]
+    public virtual Task ToString_enum_property_projection(bool async)
+        => AssertQuery(
+            async,
+            ss => ss.Set<Gear>().Select(g => g.Rank.ToString()),
+            ss => ss.Set<Gear>().Select(g => ((int)g.Rank).ToString()));
+
+    [ConditionalTheory]
+    [MemberData(nameof(IsAsyncData))]
+    public virtual Task ToString_nullable_enum_property_projection(bool async)
+        => AssertQuery(
+            async,
+            ss => ss.Set<Weapon>().Select(w => w.AmmunitionType.ToString()),
+            ss => ss.Set<Weapon>().Select(w => w.AmmunitionType != null ? ((int)w.AmmunitionType).ToString() : null));
+
+    [ConditionalTheory]
+    [MemberData(nameof(IsAsyncData))]
+    public virtual Task ToString_enum_contains(bool async)
+        => AssertQuery(
+            async,
+            ss => ss.Set<Mission>().Where(g => g.Difficulty.ToString().Contains("Med")).Select(g => g.CodeName));
+
+    [ConditionalTheory]
+    [MemberData(nameof(IsAsyncData))]
+    public virtual Task ToString_nullable_enum_contains(bool async)
+        => AssertQuery(
+            async,
+            ss => ss.Set<Weapon>().Where(w => w.AmmunitionType.ToString().Contains("1")).Select(g => g.Name),
+            ss => ss.Set<Weapon>().Where(w => w.AmmunitionType != null && ((int?)w.AmmunitionType).ToString().Contains("1")).Select(g => g.Name));
+
     [ConditionalTheory]
     [MemberData(nameof(IsAsyncData))]
     public virtual Task Include_multiple_one_to_one_and_one_to_many_self_reference(bool async)
@@ -3118,16 +3149,6 @@ public virtual Task Projecting_nullable_bool_in_conditional_works(bool async)
                         new { Prop = cg.Gear != null ? cg.Gear.HasSoulPatch : false }),
             e => e.Prop);
 
-    [ConditionalTheory]
-    [MemberData(nameof(IsAsyncData))]
-    public virtual Task Enum_ToString_is_client_eval(bool async)
-        => AssertQuery(
-            async,
-            ss =>
-                ss.Set<Gear>().OrderBy(g => g.SquadId)
-                    .ThenBy(g => g.Nickname)
-                    .Select(g => g.Rank.ToString()));
-
     [ConditionalTheory]
     [MemberData(nameof(IsAsyncData))]
     public virtual Task Correlated_collections_naked_navigation_with_ToList(bool async)

test/EFCore.Specification.Tests/TestModels/GearsOfWarModel/GearsOfWarData.cs

@@ -133,7 +133,8 @@ public static IReadOnlyList<Mission> CreateMissions()
                 Timeline = new DateTimeOffset(599898024001234567, new TimeSpan(1, 30, 0)),
                 Duration = new TimeSpan(1, 2, 3),
                 Date = new DateOnly(2020, 1, 1),
-                Time = new TimeOnly(15, 30, 10)
+                Time = new TimeOnly(15, 30, 10),
+                Difficulty = MissionDifficulty.Low
             },
             new()
             {
@@ -143,7 +144,8 @@ public static IReadOnlyList<Mission> CreateMissions()
                 Timeline = new DateTimeOffset(2, 3, 1, 8, 0, 0, new TimeSpan(-5, 0, 0)),
                 Duration = new TimeSpan(0, 1, 2, 3, 456),
                 Date = new DateOnly(1990, 11, 10),
-                Time = new TimeOnly(10, 15, 50, 500)
+                Time = new TimeOnly(10, 15, 50, 500),
+                Difficulty = MissionDifficulty.Medium
             },
             new()
             {
@@ -153,7 +155,8 @@ public static IReadOnlyList<Mission> CreateMissions()
                 Timeline = new DateTimeOffset(10, 5, 3, 12, 0, 0, new TimeSpan()),
                 Duration = new TimeSpan(0, 1, 0, 15, 456),
                 Date = new DateOnly(1, 1, 1),
-                Time = new TimeOnly(0, 0, 0)
+                Time = new TimeOnly(0, 0, 0),
+                Difficulty = MissionDifficulty.Unknown
             }
         };
 

test/EFCore.Specification.Tests/TestModels/GearsOfWarModel/Mission.cs

@@ -13,6 +13,7 @@ public class Mission
     public TimeSpan Duration { get; set; }
     public DateOnly Date { get; set; }
     public TimeOnly Time { get; set; }
+    public MissionDifficulty Difficulty { get; set; }
 
     public virtual ICollection<SquadMission> ParticipatingSquads { get; set; }
 }

test/EFCore.Specification.Tests/TestModels/GearsOfWarModel/MissionDifficulty.cs

@@ -0,0 +1,13 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+namespace Microsoft.EntityFrameworkCore.TestModels.GearsOfWarModel;
+
+public enum MissionDifficulty
+{
+    Unknown = 0,
+    Low = 1,
+    Medium = 2,
+    High = 3,
+    Extreme = 4
+}