Report -1 for statements that are not INSERT, UPDATE or DELETE

DuckDB.NET.Bindings/DuckDBStatementType.cs

@@ -20,7 +20,6 @@ public enum DuckDBStatementType
     Drop,
     Export,
     Pragma,
-    Show,
     Vacuum,
     Call,
     Set,
@@ -31,4 +30,7 @@ public enum DuckDBStatementType
     Attach,
     Detach,
     Multi,
-}
+    CopyDatabase = 28,
+    UpdateExtensions = 29,
+    MergeInto = 30,
+}

DuckDB.NET.Data/DuckDBCommand.cs

@@ -72,18 +72,33 @@ public override int ExecuteNonQuery()
 
         var results = PreparedStatement.PreparedStatement.PrepareMultiple(connection!.NativeConnection, CommandText, parameters, UseStreamingMode);
 
-        var count = 0;
+        // DbCommand.ExecuteNonQuery: "For UPDATE, INSERT, and DELETE statements, the return value is the number of
+        // rows affected by the command. For all other types of statements, the return value is -1."
+        var count = -1;
 
         foreach (var result in results)
         {
             var current = result;
-            count += (int)NativeMethods.Query.DuckDBRowsChanged(ref current);
+            if (CountsRows(NativeMethods.Query.DuckDBResultStatementType(current)))
+            {
+                count = Math.Max(count, 0) + (int)GetRowsAffected(ref current);
+            }
+
             result.Close();
         }
 
         return count;
     }
 
+    /// <summary>The statements whose affected-row count ADO.NET reports; every other statement reports -1.</summary>
+    internal static bool CountsRows(DuckDBStatementType statementType) =>
+        statementType is DuckDBStatementType.Insert or DuckDBStatementType.Update or DuckDBStatementType.Delete or DuckDBStatementType.Copy or DuckDBStatementType.MergeInto;
+
+    internal static long GetRowsAffected(ref DuckDBResult result) =>
+        NativeMethods.Query.DuckDBResultReturnType(result) == DuckDBResultType.QueryResult
+            ? NativeMethods.Query.DuckDBRowCount(ref result)
+            : NativeMethods.Query.DuckDBRowsChanged(ref result);
+
     public override object? ExecuteScalar()
     {
         EnsureConnectionOpen();
@@ -181,4 +196,4 @@ private void EnsureConnectionOpen([CallerMemberName] string operation = "")
             throw new InvalidOperationException($"{operation} requires an open connection");
         }
     }
-}
+}

DuckDB.NET.Data/DuckDBDataReader.cs

@@ -21,6 +21,7 @@ public sealed class DuckDBDataReader : DbDataReader
     private ulong rowsReadFromCurrentChunk;
 
     private bool closed;
+    private int recordsAffected = -1;
     private bool hasRows;
     private bool streamingResult;
     private bool streamEnded;
@@ -54,6 +55,11 @@ private bool InitNextReader()
         while (resultEnumerator.MoveNext())
         {
             var result = resultEnumerator.Current;
+            if (DuckDBCommand.CountsRows(NativeMethods.Query.DuckDBResultStatementType(result)))
+            {
+                recordsAffected = Math.Max(recordsAffected, 0) + (int)DuckDBCommand.GetRowsAffected(ref result);
+            }
+
             if (NativeMethods.Query.DuckDBResultReturnType(result) == DuckDBResultType.QueryResult)
             {
                 // Release the previous result set before replacing it: nothing else holds it, and a materialized
@@ -341,7 +347,11 @@ public override bool IsDBNull(int ordinal)
 
     public override object this[string name] => GetValue(GetOrdinal(name));
 
-    public override int RecordsAffected => -1;
+    /// <summary>
+    /// The rows inserted, updated, deleted, or copied by the statements read so far; -1 when none of them reports an
+    /// affected-row count. DbDataReader.RecordsAffected: "-1 for SELECT statements; 0 if no rows were affected".
+    /// </summary>
+    public override int RecordsAffected => recordsAffected;
 
     public override bool HasRows => hasRows;
 
@@ -460,4 +470,4 @@ private static void ThrowNoRowRead()
     {
         throw new InvalidOperationException("No row has been read");
     }
-}
+}

DuckDB.NET.Test/ExecuteNonQueryTests.cs

@@ -1,4 +1,6 @@
-namespace DuckDB.NET.Test;
+using DuckDB.NET.Test.Helpers;
+
+namespace DuckDB.NET.Test;
 
 public class ExecuteNonQueryTests(DuckDBDatabaseFixture db) : DuckDBTestBase(db)
 {
@@ -41,4 +43,109 @@ public void ExecuteQueryWithUnicodeText()
             results.Should().BeEquivalentTo(words);
         }
     }
-}
+
+    // https://learn.microsoft.com/dotnet/api/system.data.common.dbcommand.executenonquery:
+    // "For UPDATE, INSERT, and DELETE statements, the return value is the number of rows affected by the command.
+    // For all other types of statements, the return value is -1."
+    [Theory]
+    [InlineData("SELECT 42")]
+    [InlineData("CREATE TABLE minus_one (id INTEGER)")]
+    [InlineData("SET threads = 1")]
+    public async Task NonDmlStatementsReturnMinusOne(string sql)
+    {
+        Command.CommandText = sql;
+        Command.ExecuteNonQuery().Should().Be(-1);
+
+        Command.CommandText = sql.Replace("minus_one", "minus_one_async");
+        (await Command.ExecuteNonQueryAsync()).Should().Be(-1);
+    }
+
+    [Fact]
+    public void DmlStatementsReturnTheirRowCountIncludingZero()
+    {
+        Command.CommandText = "CREATE TABLE counted (id INTEGER); INSERT INTO counted VALUES (1), (2), (3);";
+        Command.ExecuteNonQuery().Should().Be(3, "only the INSERT is counted");
+
+        Command.CommandText = "UPDATE counted SET id = id + 10 WHERE id > 100";
+        Command.ExecuteNonQuery().Should().Be(0);
+
+        Command.CommandText = "DELETE FROM counted WHERE id = 2";
+        Command.ExecuteNonQuery().Should().Be(1);
+    }
+
+    [Fact]
+    public void MergeReportsItsRowCount()
+    {
+        Command.CommandText = "CREATE TABLE merge_counted (id INTEGER, name VARCHAR); INSERT INTO merge_counted VALUES (1, 'old');";
+        Command.ExecuteNonQuery();
+
+        Command.CommandText = "MERGE INTO merge_counted AS target USING (VALUES (1, 'updated'), (2, 'inserted')) AS source(id, name) ON target.id = source.id WHEN MATCHED THEN UPDATE SET name = source.name WHEN NOT MATCHED THEN INSERT (id, name) VALUES (source.id, source.name);";
+        Command.ExecuteNonQuery().Should().Be(2);
+    }
+
+    [Fact]
+    public void CopyReportsItsRowCount()
+    {
+        using var file = DisposableFile.GenerateInTemp("csv");
+        Command.CommandText = "CREATE TABLE copy_counted (id INTEGER); INSERT INTO copy_counted VALUES (1), (2), (3);";
+        Command.ExecuteNonQuery();
+
+        Command.CommandText = $"COPY copy_counted TO '{file.FileName}' (FORMAT CSV);";
+        Command.ExecuteNonQuery().Should().Be(3);
+    }
+
+    [Theory]
+    [InlineData(false)]
+    [InlineData(true)]
+    public void ReturningReportsItsRowCount(bool useStreamingMode)
+    {
+        var tableName = useStreamingMode ? "returning_counted_streaming" : "returning_counted_materialized";
+        using var command = new DuckDBCommand
+        {
+            Connection = Connection,
+            UseStreamingMode = useStreamingMode,
+            CommandText = $"CREATE TABLE {tableName} (id INTEGER); INSERT INTO {tableName} VALUES (1), (2);"
+        };
+        command.ExecuteNonQuery();
+
+        command.CommandText = $"INSERT INTO {tableName} VALUES (3), (4) RETURNING id;";
+        command.ExecuteNonQuery().Should().Be(2);
+
+        command.CommandText = $"UPDATE {tableName} SET id = id + 10 WHERE id <= 2 RETURNING id;";
+        using var reader = command.ExecuteReader();
+        while (reader.Read()) { }
+        reader.Close();
+        reader.RecordsAffected.Should().Be(2);
+    }
+
+    // https://learn.microsoft.com/dotnet/api/system.data.common.dbdatareader.recordsaffected:
+    // "The number of rows changed, inserted, or deleted. -1 for SELECT statements; 0 if no rows were affected"
+    [Fact]
+    public void RecordsAffectedCountsDmlRunThroughExecuteReader()
+    {
+        Command.CommandText = "CREATE TABLE through_reader (id INTEGER); INSERT INTO through_reader VALUES (1), (2);";
+        Command.ExecuteNonQuery();
+
+        Command.CommandText = "DELETE FROM through_reader WHERE id = 2";
+        using (var reader = Command.ExecuteReader())
+        {
+            reader.Close();
+            reader.RecordsAffected.Should().Be(1);
+        }
+
+        Command.CommandText = "DELETE FROM through_reader WHERE id = 99";
+        using (var reader = Command.ExecuteReader())
+        {
+            reader.Close();
+            reader.RecordsAffected.Should().Be(0);
+        }
+
+        Command.CommandText = "SELECT id FROM through_reader";
+        using (var reader = Command.ExecuteReader())
+        {
+            while (reader.Read()) { }
+            reader.Close();
+            reader.RecordsAffected.Should().Be(-1);
+        }
+    }
+}