Fix return value of ExecuteNonQuery.

It must return -1 for statements that don't modify data, e.g., SELECT.

Author: bgrainger

src/MySqlConnector/Core/ResultSet.cs

@@ -26,7 +26,7 @@ public async Task<ResultSet> ReadResultSetHeaderAsync(IOBehavior ioBehavior)
 			ColumnDefinitions = null;
 			ColumnTypes = null;
 			LastInsertId = 0;
-			RecordsAffected = 0;
+			RecordsAffected = null;
 			State = ResultSetState.None;
 			m_columnDefinitionPayloadUsedBytes = 0;
 			m_dataLengths = null;
@@ -46,7 +46,7 @@ public async Task<ResultSet> ReadResultSetHeaderAsync(IOBehavior ioBehavior)
 					if (firstByte == OkPayload.Signature)
 					{
 						var ok = OkPayload.Create(payload);
-						RecordsAffected += ok.AffectedRowCount;
+						RecordsAffected = (RecordsAffected ?? 0) + ok.AffectedRowCount;
 						LastInsertId = ok.LastInsertId;
 						ColumnDefinitions = null;
 						ColumnTypes = null;
@@ -334,7 +334,7 @@ public Row GetCurrentRow()
 		public ColumnDefinitionPayload[] ColumnDefinitions { get; private set; }
 		public MySqlDbType[] ColumnTypes { get; private set; }
 		public long LastInsertId { get; private set; }
-		public int RecordsAffected { get; private set; }
+		public int? RecordsAffected { get; private set; }
 		public ResultSetState State { get; private set; }
 
 		byte[] m_columnDefinitionPayloads;

src/MySqlConnector/MySql.Data.MySqlClient/MySqlDataReader.cs

@@ -104,7 +104,7 @@ private void ActivateResultSet(ResultSet resultSet)
 			}
 
 			Command.LastInsertedId = resultSet.LastInsertId;
-			m_recordsAffected += resultSet.RecordsAffected;
+			m_recordsAffected = m_recordsAffected == null ? resultSet.RecordsAffected : m_recordsAffected.Value + (resultSet.RecordsAffected ?? 0);
 		}
 
 		private async Task<ResultSet> BufferNextResultAsync(IOBehavior ioBehavior, CancellationToken cancellationToken)
@@ -169,7 +169,7 @@ private async Task<ResultSet> ScanResultSetAsyncAwaited(IOBehavior ioBehavior, R
 
 		public override bool HasRows => GetResultSet().HasRows;
 		public override bool IsClosed => Command == null;
-		public override int RecordsAffected => m_recordsAffected;
+		public override int RecordsAffected => m_recordsAffected.GetValueOrDefault(-1);
 
 		public override int GetOrdinal(string name) => GetResultSet().GetOrdinal(name);
 
@@ -441,7 +441,7 @@ private ResultSet GetResultSet()
 		}
 
 		readonly CommandBehavior m_behavior;
-		int m_recordsAffected;
+		int? m_recordsAffected;
 		ResultSet m_resultSet;
 		ResultSet m_resultSetBuffered;
 #if !NETSTANDARD1_3

tests/SideBySide/CommandTests.cs

@@ -1,4 +1,6 @@
 using System;
+using System.Threading.Tasks;
+using Dapper;
 using MySql.Data.MySqlClient;
 using Xunit;
 
@@ -58,6 +60,33 @@ public void PrepareRequiresOpenConnection()
 			}
 		}
 
+		[Fact]
+		public void ExecuteNonQueryForSelectReturnsNegativeOne()
+		{
+			using (var connection = new MySqlConnection(m_database.Connection.ConnectionString))
+			using (var command = connection.CreateCommand())
+			{
+				connection.Open();
+				command.CommandText = "SELECT 1;";
+				Assert.Equal(-1, command.ExecuteNonQuery());
+			}
+		}
+
+		[Fact]
+		public async Task ExecuteNonQueryReturnValue()
+		{
+			using (var connection = new MySqlConnection(m_database.Connection.ConnectionString))
+			{
+				await connection.OpenAsync();
+				await connection.ExecuteAsync(@"drop table if exists execute_non_query;
+create table execute_non_query(id integer not null primary key auto_increment, value text null);");
+				Assert.Equal(4, await connection.ExecuteAsync("insert into execute_non_query(value) values(null), (null), ('one'), ('two');"));
+				Assert.Equal(-1, await connection.ExecuteAsync("select value from execute_non_query;"));
+				Assert.Equal(2, await connection.ExecuteAsync("delete from execute_non_query where value is null;"));
+				Assert.Equal(1, await connection.ExecuteAsync("update execute_non_query set value = 'three' where value = 'one';"));
+			}
+		}
+
 		readonly DatabaseFixture m_database;
 	}
 }