Translate ToString() on string expressions

src/EFCore.PG/Query/ExpressionTranslators/Internal/NpgsqlObjectToStringTranslator.cs

@@ -65,6 +65,11 @@ public NpgsqlObjectToStringTranslator(IRelationalTypeMappingSource typeMappingSo
             return null;
         }
 
+        if (instance.TypeMapping?.ClrType == typeof(string))
+        {
+            return instance;
+        }
+
         if (instance.Type == typeof(bool))
         {
             if (instance.Type == typeof(bool))

test/EFCore.PG.FunctionalTests/Query/GearsOfWarQueryNpgsqlTest.cs

@@ -13,6 +13,17 @@ public GearsOfWarQueryNpgsqlTest(GearsOfWarQueryNpgsqlFixture fixture, ITestOutp
         Fixture.TestSqlLoggerFactory.SetTestOutputHelper(testOutputHelper);
     }
 
+    public override async Task ToString_string_property_projection(bool async)
+    {
+        await base.ToString_string_property_projection(async);
+
+        AssertSql(
+            """
+SELECT w."Name"
+FROM "Weapons" AS w
+""");
+    }
+
     #region Byte array
 
     public override async Task Byte_array_filter_by_length_literal_does_not_cast_on_varbinary_n(bool async)

test/EFCore.PG.FunctionalTests/Query/Inheritance/TPCGearsOfWarQueryNpgsqlTest.cs

@@ -11,6 +11,17 @@ public TPCGearsOfWarQueryNpgsqlTest(TPCGearsOfWarQueryNpgsqlFixture fixture, ITe
         Fixture.TestSqlLoggerFactory.SetTestOutputHelper(testOutputHelper);
     }
 
+    public override async Task ToString_string_property_projection(bool async)
+    {
+        await base.ToString_string_property_projection(async);
+
+        AssertSql(
+            """
+SELECT w."Name"
+FROM "Weapons" AS w
+""");
+    }
+
     // Base implementation uses DateTimeOffset.Now, which we don't translate by design. Use DateTimeOffset.UtcNow instead.
     public override async Task Select_datetimeoffset_comparison_in_projection(bool async)
     {

test/EFCore.PG.FunctionalTests/Query/Inheritance/TPTGearsOfWarQueryNpgsqlTest.cs

@@ -15,6 +15,17 @@ public TPTGearsOfWarQueryNpgsqlTest(TPTGearsOfWarQueryNpgsqlFixture fixture, ITe
     // TODO: #1232
     // protected override bool CanExecuteQueryString => true;
 
+    public override async Task ToString_string_property_projection(bool async)
+    {
+        await base.ToString_string_property_projection(async);
+
+        AssertSql(
+            """
+SELECT w."Name"
+FROM "Weapons" AS w
+""");
+    }
+
     // Base implementation uses DateTimeOffset.Now, which we don't translate by design. Use DateTimeOffset.UtcNow instead.
     public override async Task Select_datetimeoffset_comparison_in_projection(bool async)
     {

test/EFCore.PG.FunctionalTests/Query/Translations/StringTranslationsNpgsqlTest.cs

@@ -115,6 +115,75 @@ SELECT lower(b."String")
 """);
     }
 
+    [ConditionalFact]
+    public async Task ToString_on_string()
+    {
+        await AssertQuery(
+            ss => ss.Set<BasicTypesEntity>().Where(b => b.String.ToString() == "Seattle").Select(b => b.String));
+
+        AssertSql(
+            """
+SELECT b."String"
+FROM "BasicTypesEntities" AS b
+WHERE b."String" = 'Seattle'
+""");
+    }
+
+    [ConditionalFact]
+    public async Task ToString_on_nullable_string()
+    {
+        await AssertQuery(
+            ss => ss.Set<NullableBasicTypesEntity>().Where(b => b.String!.ToString() == null).Select(b => b.Id),
+            ss => ss.Set<NullableBasicTypesEntity>().Where(b => b.String == null).Select(b => b.Id));
+
+        AssertSql(
+            """
+SELECT n."Id"
+FROM "NullableBasicTypesEntities" AS n
+WHERE n."String" IS NULL
+""");
+    }
+
+    [ConditionalFact]
+    public async Task ToString_on_object_typed_string_grouping_key_order_by()
+    {
+        await AssertQuery(
+            ss => ss.Set<BasicTypesEntity>()
+                .Where(b => b.String == "Seattle" || b.String == "Berlin")
+                .GroupBy(b => (object)b.String)
+                .Select(g => new { Key = g.Key.ToString(), Count = g.Count() })
+                .OrderBy(g => g.Key),
+            assertOrder: true);
+
+        AssertSql(
+            """
+SELECT b."String", count(*)::int
+FROM "BasicTypesEntities" AS b
+WHERE b."String" IN ('Seattle', 'Berlin')
+GROUP BY b."String"
+ORDER BY b."String" NULLS FIRST
+""");
+    }
+
+    [ConditionalFact]
+    public async Task ToString_on_object_typed_string_grouping_key_where()
+    {
+        await AssertQuery(
+            ss => ss.Set<BasicTypesEntity>()
+                .GroupBy(b => (object)b.String)
+                .Select(g => new { Key = g.Key.ToString(), Count = g.Count() })
+                .Where(g => g.Key == "Seattle"),
+            elementSorter: g => g.Key);
+
+        AssertSql(
+            """
+SELECT b."String", count(*)::int
+FROM "BasicTypesEntities" AS b
+GROUP BY b."String"
+HAVING b."String" = 'Seattle'
+""");
+    }
+
     #endregion Miscellaneous
 
     #region IndexOf