First, change the type of your
List<string> (you can change
string to another type if needed, like
Now your controller will get the list of selected values, but then your query must save them. Ideally, this list should be saved in another table and you should save each value in a separate row. That's a good normalized design.
However, it seems from your code that you save the list in a single field of the same table, perhaps comma-separated? That's not a good design and it needs to be normalized like I mentioned above, but if you really want to do so then you have to join the array items using the separator that you want:
If you're using .NET < 4, you have to use
Note: your query is vulnerable to SQL injection. Use a parameterized query instead.