Throw standard exceptions from Prepare.

Author: bgrainger

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

@@ -72,6 +72,11 @@ public override object ExecuteScalar()
 
 		public override void Prepare()
 		{
+			if (Connection == null)
+				throw new InvalidOperationException("Connection property must be non-null.");
+			if (Connection.State != ConnectionState.Open)
+				throw new InvalidOperationException("Connection must be Open; current state is {0}".FormatInvariant(Connection.State));
+
 			// NOTE: Prepared statements in MySQL are not currently supported.
 			// 1) Only a subset of statements are actually preparable by the server: http://dev.mysql.com/worklog/task/?id=2871
 			// 2) Although CLIENT_MULTI_STATEMENTS is supposed to mean that the Server "Can handle multiple statements per COM_QUERY and COM_STMT_PREPARE" (https://dev.mysql.com/doc/internals/en/capability-flags.html#flag-CLIENT_MULTI_STATEMENTS),

tests/SideBySide/CommandTests.cs

@@ -39,6 +39,25 @@ public void ExecuteReaderRequiresOpenConnection()
 			}
 		}
 
+		[Fact]
+		public void PrepareRequiresConnection()
+		{
+			using (var command = new MySqlCommand())
+			{
+				Assert.Throws<InvalidOperationException>(() => command.Prepare());
+			}
+		}
+
+		[Fact]
+		public void PrepareRequiresOpenConnection()
+		{
+			using (var connection = new MySqlConnection())
+			using (var command = connection.CreateCommand())
+			{
+				Assert.Throws<InvalidOperationException>(() => command.Prepare());
+			}
+		}
+
 		readonly DatabaseFixture m_database;
 	}
 }