Fix migration issues on MSSQL

Author: iMattPro

migrations/handle_subscriptions.php

@@ -98,9 +98,24 @@ public function copy_subscription_tables()
 				$core_push_subscriptions_table => $wpn_push_subscriptions_table
 			] as $core_table => $ext_table)
 		{
+			// Turn on identity insert on mssql to be able to insert into
+			// identity columns (e.g. id)
+			if (strpos($this->db->sql_layer, 'mssql') !== false)
+			{
+				$sql = 'SET IDENTITY_INSERT ' . $core_table . ' ON';
+				$this->db->sql_query($sql);
+			}
+
 			$sql = 'INSERT INTO ' . $core_table . '
 					SELECT * FROM ' . $ext_table;
 			$this->db->sql_query($sql);
+
+			// Disable identity insert on mssql again
+			if (strpos($this->db->sql_layer, 'mssql') !== false)
+			{
+				$sql = 'SET IDENTITY_INSERT ' . $core_table . ' OFF';
+				$this->db->sql_query($sql);
+			}
 		}
 	}
 }