Question

I retrieved a list of users from database, something like

List<User> users = <..list of users from db...> 

Name, LastName, DateOfBirth //multidimensional array??

Now I want to store this list as a string and I want be able to reuse it i.e.

string strUsers = users.ToArray().ToString();

How to recreate a list of users from strUsers?

Is it possible?

Answer 1

If you have a lot of users and a lot of columns, it would be better to write your own custom converter class.

public static class UsersConverter
{
    // Separates user properties.
    private const char UserDataSeparator = ',';

    // Separates users in the list.
    private const char UsersSeparator = ';';

    public static string ConvertListToString(IEnumerable<User> usersList)
    {
        var stringBuilder = new StringBuilder();

        // Build the users string.
        foreach (User user in usersList)
        {
            stringBuilder.Append(user.Name);
            stringBuilder.Append(UserDataSeparator);
            stringBuilder.Append(user.Age);
            stringBuilder.Append(UsersSeparator);
        }

        // Remove trailing separator.
        stringBuilder.Remove(stringBuilder.Length - 1, 1);

        return stringBuilder.ToString();
    }

    public static List<User> ParseStringToList(string usersString)
    {
        // Check that passed argument is not null.
        if (usersString == null) throw new ArgumentNullException("usersString");

        var result = new List<User>();

        string[] userDatas = usersString.Split(UsersSeparator);

        foreach (string[] userData in userDatas.Select(x => x.Split(UserDataSeparator)))
        {
            // Check that user data contains enough arguments.
            if (userData.Length < 2) throw new ArgumentException("Users string contains invalid data.");

            string name = userData[0];
            int age;

            // Try parsing age.
            if (!int.TryParse(userData[1], out age))
            {
                throw new ArgumentException("Users string contains invalid data.");
            }

            // Add to result list.
            result.Add(new User { Name = name, Age = age });
        }

        return result;
    }
}

You will win performance wise using the StringBuilder to build up your users string. You could also easily expand the converter to take account different separators/additional logic etc.

If you need a more generic solution (to be able to use for any class), you could create a converter which uses reflection to iterate over all the public fields, get/set properties to see what can be extracted as string and later reverse the process to convert your string back to the list.