[release/7.0] Fix to #30358 - Duplicate table alias in generated select query (An item with the same key has already been added)

src/EFCore.Relational/Query/SqlExpressions/SelectExpression.Helper.cs

@@ -385,6 +385,9 @@ public int GetHashCode((ColumnExpression Column, ValueComparer Comparer) obj)
 
     private sealed class AliasUniquifier : ExpressionVisitor
     {
+        private static readonly bool UseOldBehavior30358
+            = AppContext.TryGetSwitch("Microsoft.EntityFrameworkCore.Issue30358", out var enabled30358) && enabled30358;
+
         private readonly HashSet<string> _usedAliases;
         private readonly List<SelectExpression> _visitedSelectExpressions = new();
 
@@ -401,7 +404,30 @@ public AliasUniquifier(HashSet<string> usedAliases)
             {
                 for (var i = 0; i < innerSelectExpression._tableReferences.Count; i++)
                 {
-                    var newAlias = GenerateUniqueAlias(_usedAliases, innerSelectExpression._tableReferences[i].Alias);
+                    string newAlias;
+                    if (UseOldBehavior30358)
+                    {
+                        newAlias = GenerateUniqueAlias(_usedAliases, innerSelectExpression._tableReferences[i].Alias);
+                    }
+                    else
+                    {
+                        var currentAlias = innerSelectExpression._tableReferences[i].Alias;
+                        newAlias = GenerateUniqueAlias(_usedAliases, currentAlias);
+
+                        if (newAlias != currentAlias)
+                        {
+                            // we keep the old alias in the list (even though it's not actually being used anymore)
+                            // to disambiguate the APPLY case, e.g. something like this:
+                            // SELECT * FROM EntityOne as e
+                            // OUTER APPLY (
+                            //    SELECT * FROM EntityTwo as e1
+                            //    LEFT JOIN EntityThree as e ON (...) -- reuse alias e, since we use e1 after uniqification
+                            //    WHERE e.Foo == e1.Bar -- ambiguity! e could refer to EntityOne or EntityThree
+                            // ) as t
+                            innerSelectExpression._usedAliases.Add(newAlias);
+                        }
+                    }
+
                     innerSelectExpression._tableReferences[i].Alias = newAlias;
                     UnwrapJoinExpression(innerSelectExpression._tables[i]).Alias = newAlias;
                 }

test/EFCore.Relational.Specification.Tests/Query/OwnedEntityQueryRelationalTestBase.cs

@@ -369,6 +369,91 @@ public class Rut
         public int? Value { get; set; }
     }
 
+    [ConditionalTheory]
+    [MemberData(nameof(IsAsyncData))]
+    public virtual async Task Join_selects_with_duplicating_aliases_and_owned_expansion_uniquifies_correctly(bool async)
+    {
+        var contextFactory = await InitializeAsync<MyContext30358>(seed: c => c.Seed());
+        using var context = contextFactory.CreateContext();
+
+        var query = from monarch in context.Monarchs
+                    join magus in context.Magi.Where(x => x.Name.Contains("Bayaz")) on monarch.RulerOf equals magus.Affiliation
+                    select new { monarch, magus };
+
+        var result = async ? await query.ToListAsync() : query.ToList();
+
+        Assert.Single(result);
+        Assert.Equal("The Union", result[0].monarch.RulerOf);
+        Assert.Equal("The Divider", result[0].magus.ToolUsed.Name);
+    }
+
+    protected class MyContext30358 : DbContext
+    {
+        public DbSet<Monarch30358> Monarchs { get; set; }
+        public DbSet<Magus30358> Magi { get; set; }
+
+        public MyContext30358(DbContextOptions options)
+           : base(options)
+        {
+        }
+
+        protected override void OnModelCreating(ModelBuilder modelBuilder)
+        {
+            modelBuilder.Entity<Magus30358>().OwnsOne(x => x.ToolUsed, x => x.ToTable("MagicTools"));
+        }
+
+        public void Seed()
+        {
+            Add(new Monarch30358
+            {
+                Name = "His August Majesty Guslav the Fifth",
+                RulerOf = "The Union",
+            });
+
+            Add(new Monarch30358
+            {
+                Name = "Emperor Uthman-ul-Dosht",
+                RulerOf = "The Gurkish Empire",
+            });
+
+            Add(new Magus30358
+            {
+                Name = "Bayaz, the First of the Magi",
+                Affiliation = "The Union",
+                ToolUsed = new MagicTool30358 { Name = "The Divider" }
+            });
+
+            Add(new Magus30358
+            {
+                Name = "The Prophet Khalul",
+                Affiliation = "The Gurkish Empire",
+                ToolUsed = new MagicTool30358 { Name = "The Hundred Words" }
+            });
+
+            SaveChanges();
+        }
+    }
+
+    public class Monarch30358
+    {
+        public int Id { get; set; }
+        public string Name { get; set; }
+        public string RulerOf { get; set; }
+    }
+
+    public class Magus30358
+    {
+        public int Id { get; set; }
+        public string Name { get; set; }
+        public string Affiliation { get; set; }
+        public MagicTool30358 ToolUsed { get; set; }
+    }
+
+    public class MagicTool30358
+    {
+        public string Name { get; set; }
+    }
+
     protected override DbContextOptionsBuilder AddOptions(DbContextOptionsBuilder builder)
         => base.AddOptions(builder).ConfigureWarnings(
             c => c

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

@@ -178,6 +178,23 @@ public override async Task Owned_entity_with_all_null_properties_property_access
 """
 SELECT [r].[Rot_ApartmentNo]
 FROM [RotRutCases] AS [r]
+""");
+    }
+
+    public override async Task Join_selects_with_duplicating_aliases_and_owned_expansion_uniquifies_correctly(bool async)
+    {
+        await base.Join_selects_with_duplicating_aliases_and_owned_expansion_uniquifies_correctly(async);
+
+        AssertSql(
+"""
+SELECT [m].[Id], [m].[Name], [m].[RulerOf], [t].[Id], [t].[Affiliation], [t].[Name], [t].[Magus30358Id], [t].[Name0]
+FROM [Monarchs] AS [m]
+INNER JOIN (
+    SELECT [m0].[Id], [m0].[Affiliation], [m0].[Name], [m1].[Magus30358Id], [m1].[Name] AS [Name0]
+    FROM [Magi] AS [m0]
+    LEFT JOIN [MagicTools] AS [m1] ON [m0].[Id] = [m1].[Magus30358Id]
+    WHERE [m0].[Name] LIKE N'%Bayaz%'
+) AS [t] ON [m].[RulerOf] = [t].[Affiliation]
 """);
     }
 }