Refine validation to allow all-primary-key columns with DeleteNotMatchedBySource

- Update validation to allow Upsert mode with only primary key columns when DeleteNotMatchedBySource is true
- This enables valid use case of syncing which records exist without updating other columns
- Add test case to verify this scenario passes validation

Co-authored-by: philnach <[email protected]>

Author: Copilot

Extensions/SqlServer/Cosmos.DataTransfer.SqlServerExtension.UnitTests/SqlServerSinkSettingsTests.cs

@@ -196,12 +196,35 @@ public void TestSinkSettings_AllColumnsArePrimaryKeys_FailsValidation()
         var validationResults = settings.Validate(new ValidationContext(settings)).ToList();
 
         Assert.IsTrue(validationResults.Any(v => v.MemberNames.Contains(nameof(SqlServerSinkSettings.ColumnMappings))),
-            "Validation should fail when all columns are primary keys");
+            "Validation should fail when all columns are primary keys without DeleteNotMatchedBySource");
 
         Assert.IsTrue(validationResults.Any(v => v.ErrorMessage!.Contains("non-primary key column")),
             "Validation error should mention non-primary key column requirement");
     }
 
+    [TestMethod]
+    public void TestSinkSettings_AllColumnsArePrimaryKeys_WithDelete_PassesValidation()
+    {
+        var settings = new SqlServerSinkSettings
+        {
+            ConnectionString = "Server=.;Database=Test;",
+            TableName = "TestTable",
+            WriteMode = SqlWriteMode.Upsert,
+            PrimaryKeyColumns = new List<string> { "Id", "Name" },
+            DeleteNotMatchedBySource = true,
+            ColumnMappings = new List<ColumnMapping>
+            {
+                new ColumnMapping { ColumnName = "Id" },
+                new ColumnMapping { ColumnName = "Name" }
+            }
+        };
+
+        var validationResults = settings.Validate(new ValidationContext(settings)).ToList();
+        
+        Assert.IsFalse(validationResults.Any(v => v.MemberNames.Contains(nameof(SqlServerSinkSettings.ColumnMappings))),
+            "Validation should pass when all columns are primary keys but DeleteNotMatchedBySource is true");
+    }
+
     [TestMethod]
     public void TestSinkSettings_DeleteNotMatchedBySource_DefaultsToFalse()
     {

Extensions/SqlServer/Cosmos.DataTransfer.SqlServerExtension/SqlServerSinkSettings.cs

@@ -53,14 +53,14 @@ public IEnumerable<ValidationResult> Validate(ValidationContext validationContex
                 }
                 else
                 {
-                    // Ensure at least one non-key column exists for updates
+                    // Ensure at least one non-key column exists for updates, unless we're only doing DELETE sync
                     var allColumns = ColumnMappings.Select(m => m.ColumnName).ToList();
                     var nonKeyColumns = allColumns.Except(PrimaryKeyColumns).ToList();
 
-                    if (nonKeyColumns.Count == 0)
+                    if (nonKeyColumns.Count == 0 && !DeleteNotMatchedBySource)
                     {
                         results.Add(new ValidationResult(
-                            "At least one non-primary key column must be specified in ColumnMappings for Upsert mode.",
+                            "At least one non-primary key column must be specified in ColumnMappings for Upsert mode, or set DeleteNotMatchedBySource to true.",
                             new[] { nameof(ColumnMappings) }));
                     }
                 }