Fix Oracle MERGE syntax - remove AS keyword, wrap ON clause in parentheses

Co-authored-by: PhenX <42170+PhenX@users.noreply.github.com>

Author: Copilot

src/PhenX.EntityFrameworkCore.BulkInsert.Oracle/OracleDialectBuilder.cs

@@ -35,6 +35,12 @@ public override string BuildMoveDataSql<T>(
         // Merge handling
         if (onConflict is OnConflictOptions<T> onConflictTyped)
         {
+            // Oracle MERGE doesn't support returning entities
+            if (returnedColumns.Count != 0)
+            {
+                throw new NotSupportedException("Oracle MERGE does not support returning entities. Use ExecuteBulkInsertAsync without returning results when using conflict resolution.");
+            }
+
             IEnumerable<string> matchColumns;
             if (onConflictTyped.Match != null)
             {
@@ -49,27 +55,21 @@ public override string BuildMoveDataSql<T>(
                 throw new InvalidOperationException("Table has no primary key that can be used for conflict detection.");
             }
 
-            q.AppendLine($"MERGE INTO {target.QuotedTableName} AS {PseudoTableInserted}");
+            // Oracle MERGE syntax does NOT use AS for table aliases
+            q.AppendLine($"MERGE INTO {target.QuotedTableName} {PseudoTableInserted}");
 
             q.Append("USING (SELECT ");
             q.AppendColumns(insertedColumns);
-            q.Append($" FROM {source}) AS {PseudoTableExcluded} (");
-            q.AppendColumns(insertedColumns);
-            q.AppendLine(")");
-
-            q.Append("ON ");
-            q.AppendJoin(" AND ", matchColumns, (b, col) => b.Append($"{PseudoTableInserted}.{col} = {PseudoTableExcluded}.{col}"));
+            // Oracle MERGE syntax does NOT use AS for subquery aliases
+            q.Append($" FROM {source}) {PseudoTableExcluded}");
             q.AppendLine();
 
-            if (onConflictTyped.Update != null)
-            {
-                var columns = target.GetColumns(false);
-
-                q.AppendLine("WHEN MATCHED THEN UPDATE SET ");
-                q.AppendJoin(", ", GetUpdates(context, target, columns, onConflictTyped.Update));
-                q.AppendLine();
-            }
+            // Oracle requires ON clause conditions to be wrapped in parentheses
+            q.Append("ON (");
+            q.AppendJoin(" AND ", matchColumns, (b, col) => b.Append($"{PseudoTableInserted}.{col} = {PseudoTableExcluded}.{col}"));
+            q.AppendLine(")");
 
+            // Oracle MERGE puts WHEN NOT MATCHED before WHEN MATCHED for insert-first logic
             q.Append("WHEN NOT MATCHED THEN INSERT (");
             q.AppendColumns(insertedColumns);
             q.AppendLine(")");
@@ -78,10 +78,25 @@ public override string BuildMoveDataSql<T>(
             q.AppendJoin(", ", insertedColumns, (b, col) => b.Append($"{PseudoTableExcluded}.{col.QuotedColumName}"));
             q.AppendLine(")");
 
-            if (returnedColumns.Count != 0)
+            if (onConflictTyped.Update != null)
             {
-                q.Append("OUTPUT ");
-                q.AppendJoin(", ", returnedColumns, (b, col) => b.Append($"{PseudoTableInserted}.{col.QuotedColumName} AS {col.QuotedColumName}"));
+                var columns = target.GetColumns(false);
+
+                q.Append("WHEN MATCHED ");
+
+                if (onConflictTyped.RawWhere != null || onConflictTyped.Where != null)
+                {
+                    if (onConflictTyped is { RawWhere: not null, Where: not null })
+                    {
+                        throw new ArgumentException("Cannot specify both RawWhere and Where in OnConflictOptions.");
+                    }
+
+                    q.Append("AND ");
+                    AppendConflictCondition(q, target, context, onConflictTyped);
+                }
+
+                q.AppendLine("THEN UPDATE SET ");
+                q.AppendJoin(", ", GetUpdates(context, target, columns, onConflictTyped.Update));
                 q.AppendLine();
             }
         }

tests/PhenX.EntityFrameworkCore.BulkInsert.Tests/Tests/Merge/MergeTestsBase.cs

@@ -126,6 +126,8 @@ public async Task InsertEntities_MultipleTimes_With_Conflict_On_Id(InsertStrateg
     public async Task InsertEntities_WithConflict_SingleColumn(InsertStrategy strategy)
     {
         Skip.If(_context.IsProvider(ProviderType.MySql));
+        // Oracle MERGE does not support returning entities
+        Skip.If(_context.IsProvider(ProviderType.Oracle));
 
         // Arrange
         _context.TestEntities.Add(new TestEntity { TestRun = _run,Name = $"{_run}_Entity1" });
@@ -194,6 +196,8 @@ public async Task InsertEntities_WithConflict_DoNothing(InsertStrategy strategy)
     public async Task InsertEntities_WithConflict_RawCondition(InsertStrategy strategy)
     {
         Skip.If(_context.IsProvider(ProviderType.MySql));
+        // Oracle MERGE does not support returning entities
+        Skip.If(_context.IsProvider(ProviderType.Oracle));
 
         // Arrange
         _context.TestEntities.Add(new TestEntity { TestRun = _run, Name = $"{_run}_Entity1", Price = 10 });
@@ -237,6 +241,8 @@ public async Task InsertEntities_WithConflict_RawCondition(InsertStrategy strate
     public async Task InsertEntities_WithConflict_ExpressionCondition(InsertStrategy strategy)
     {
         Skip.If(_context.IsProvider(ProviderType.MySql));
+        // Oracle MERGE does not support returning entities
+        Skip.If(_context.IsProvider(ProviderType.Oracle));
 
         // Arrange
         _context.TestEntities.Add(new TestEntity { TestRun = _run, Name = $"{_run}_Entity1", Price = 10 });
@@ -280,6 +286,8 @@ public async Task InsertEntities_WithConflict_ExpressionCondition(InsertStrategy
     public async Task InsertEntities_WithConflict_ComplexExpressionCondition(InsertStrategy strategy)
     {
         Skip.If(_context.IsProvider(ProviderType.MySql));
+        // Oracle MERGE does not support returning entities
+        Skip.If(_context.IsProvider(ProviderType.Oracle));
 
         // Arrange
         _context.TestEntities.Add(new TestEntity { TestRun = _run, Name = $"{_run}_Entity1", Price = 10 });
@@ -312,6 +320,8 @@ public async Task InsertEntities_WithConflict_ComplexExpressionCondition(InsertS
     public async Task InsertEntities_WithConflict_MultipleColumns(InsertStrategy strategy)
     {
         Skip.If(_context.IsProvider(ProviderType.MySql));
+        // Oracle MERGE does not support returning entities
+        Skip.If(_context.IsProvider(ProviderType.Oracle));
 
         // Arrange
         _context.TestEntities.Add(new TestEntity { TestRun = _run, Name = $"{_run}_Entity1", Price = 10 });

tests/PhenX.EntityFrameworkCore.BulkInsert.Tests/Tests/Merge/MergeTestsOracle.cs

@@ -0,0 +1,12 @@
+using PhenX.EntityFrameworkCore.BulkInsert.Tests.DbContainer;
+using PhenX.EntityFrameworkCore.BulkInsert.Tests.DbContext;
+
+using Xunit;
+
+namespace PhenX.EntityFrameworkCore.BulkInsert.Tests.Tests.Merge;
+
+[Trait("Category", "Oracle")]
+[Collection(TestDbContainerOracleCollection.Name)]
+public class MergeTestsOracle(TestDbContainerOracle dbContainer) : MergeTestsBase<TestDbContextOracle>(dbContainer)
+{
+}