Throw InvalidOperationException for open reader.

This is a breaking change from Connector/NET but is more consistent with other ADO.NET Providers. Since it indicates misuse of the library, the specific exception type should not be relied on my clients.

Author: bgrainger

docs/content/tutorials/migrating-from-connector-net.md

@@ -76,6 +76,11 @@ Connector/NET allows a command to be executed even when `MySqlCommand.Transactio
 disposed `MySqlTransaction`. MySqlConnector will throw an `InvalidOperationException` if the `MySqlCommand.Transaction`
 property doesn't reference the active transaction. See [#333](https://github.com/mysql-net/MySqlConnector/issues/333) for more details.
 
+### Exceptions
+
+For consistency with other ADO.NET providers, MySqlConnector will throw `InvalidOperationException` (instead of `MySqlException`)
+for various precondition checks that indicate misuse of the API (and not a problem related to MySQL Server).
+
 ### Bugs present in Connector/NET that are fixed in MySqlConnector
 
 * [#37283](https://bugs.mysql.com/bug.php?id=37283), [#70587](https://bugs.mysql.com/bug.php?id=70587): Distributed transactions are not supported

src/MySqlConnector/Core/ServerSession.cs

@@ -115,7 +115,7 @@ public void StartQuerying(MySqlCommand command)
 			lock (m_lock)
 			{
 				if (m_state == State.Querying || m_state == State.CancelingQuery)
-					throw new MySqlException("There is already an open DataReader associated with this Connection which must be closed first.");
+					throw new InvalidOperationException("There is already an open DataReader associated with this Connection which must be closed first.");
 
 				VerifyState(State.Connected);
 				m_state = State.Querying;

tests/SideBySide/QueryTests.cs

@@ -198,6 +198,11 @@ public async Task InvalidSql()
 		[Fact]
 		public async Task MultipleReaders()
 		{
+#if BASELINE
+			var exceptionType = typeof(MySqlException);
+#else
+			var exceptionType = typeof(InvalidOperationException);
+#endif
 			using (var cmd = m_database.Connection.CreateCommand())
 			{
 				cmd.CommandText = @"drop table if exists query_multiple_readers;
@@ -214,21 +219,21 @@ public async Task MultipleReaders()
 
 				using (var reader1 = await cmd1.ExecuteReaderAsync())
 				{
-					Assert.Throws<MySqlException>(() => cmd2.ExecuteReader());
-					Assert.Throws<MySqlException>(() => cmd2.ExecuteScalar());
+					Assert.Throws(exceptionType, () => cmd2.ExecuteReader());
+					Assert.Throws(exceptionType, () => cmd2.ExecuteScalar());
 					do
 					{
 						while (await reader1.ReadAsync())
 						{
-							Assert.Throws<MySqlException>(() => cmd2.ExecuteReader());
-							Assert.Throws<MySqlException>(() => cmd2.ExecuteScalar());
+							Assert.Throws(exceptionType, () => cmd2.ExecuteReader());
+							Assert.Throws(exceptionType, () => cmd2.ExecuteScalar());
 						}
-						Assert.Throws<MySqlException>(() => cmd2.ExecuteReader());
-						Assert.Throws<MySqlException>(() => cmd2.ExecuteScalar());
+						Assert.Throws(exceptionType, () => cmd2.ExecuteReader());
+						Assert.Throws(exceptionType, () => cmd2.ExecuteScalar());
 					} while (await reader1.NextResultAsync());
 
-					Assert.Throws<MySqlException>(() => cmd2.ExecuteReader());
-					Assert.Throws<MySqlException>(() => cmd2.ExecuteScalar());
+					Assert.Throws(exceptionType, () => cmd2.ExecuteReader());
+					Assert.Throws(exceptionType, () => cmd2.ExecuteScalar());
 
 					reader1.Dispose();
 					using (cmd2.ExecuteReader())