C# list<string> in a list<string>[] .toList()

Question

I am currently learning how to use database connections and how to read and write data. I am using Mysql data/connector 6.1 for visual studio. This supports access to a localhost mysql server.

I want to display personal information of the person logged in for which i use this code:

string query = "SELECT * FROM gebruiker WHERE id='" + id + "'";

List<string>[] list = new List<string>[5];
list[0] = new List<string>();
list[1] = new List<string>();
list[2] = new List<string>();
list[3] = new List<string>();
list[4] = new List<string>();


if (this.openConnection() == true)
{

    MySqlCommand cmd = new MySqlCommand(query, connection);
    //Een nieuw datareader object maken en dan query uitvoeren
    MySqlDataReader dataReader = cmd.ExecuteReader();


    while (dataReader.Read())
    {
        list[0].Add(dataReader["id"].ToString());
        list[1].Add(dataReader["voornaam"].ToString());
        list[2].Add(dataReader["achternaam"].ToString());
        list[3].Add(dataReader["geboortedatum"].ToString());
        list[4].Add(dataReader["Rol_id"].ToString());
    }

    dataReader.Close();

    this.closeConnection();

    return list;
}

I use Lists because I am following this tutorial: tutorial

Then when i return the list i want to get that data and add it to labels on my winform. this is the code i use:

DBconnect connectDB = new DBconnect();
List<string>[] persGegevens = connectDB.persoonlijkeGegevens(userId);
for (int i = 0; i <= persGegevens.Count(); i++)
{
    switch (i)
    {
        case 0:
            break;
        case 1:
            lblVoornaamVrbl.Text = persGegevens[i].ToString();
            break;
        case 2:
            lblAchternaamVrbl.Text = persGegevens[i].ToString();
            break;
        case 3:
            lblGbrtedatumVrbl.Text = persGegevens[i].ToString();
            break;
        case 4:
            lblFuntieVrbl.Text = persGegevens[i].ToString();
            break;
        default:
            break;
    }
}

But unfortunatly the code does not convert the data in List toString but the element will get converted toString. This is what i get: system.collections.generic.list`1[system.string] I also tried to do this with a foreach but that did not work because i can't specify which element has to be placed in what label.

Do you guys know what is the problem here? and is this the right way to retrieve data? or should i use something else to store my data?

Use a DataTable to make your code easier to work with stackoverflow.com/questions/11993211/… — Murray Foxcroft
– Murray Foxcroft, Commented May 26, 2016 at 12:54
@MurrayFoxcroft Never has using a DataTable for something like this made anything easier, in my experience — Jonesopolis
– Jonesopolis, Commented May 26, 2016 at 12:56
I would recommending looking into using Entity Framework and Linq it may make things a little easier for you to understand. — Brandon Johnson
– Brandon Johnson, Commented May 26, 2016 at 12:56
You should be using MySqlCommand parameters and not passing in id directly to the string. Take a look here for more info — Hill
– Hill, Commented May 26, 2016 at 12:59

Tommaso Cerutti · Accepted Answer · 2016-05-26 13:47:22Z

I think nik0lias suggestion is formerly correct but maybe it can runs as desired if changed to :

    case 1:
        lblVoornaamVrbl.Text = persGegevens[i][ 0 ].ToString();
        break;
    case 2:
        lblAchternaamVrbl.Text = persGegevens[i][ 0 ].ToString();
        break;
    case 3:
        lblGbrtedatumVrbl.Text = persGegevens[i][ 0 ].ToString();
        break;
    case 4:
        lblFuntieVrbl.Text = persGegevens[i][ 0 ].ToString();

If I am right, consider if a List array List<>[] is needed or you can simplify your code with List this way:

    string query = "SELECT * FROM gebruiker WHERE id='" + id + "'";

    List<string> listGebruiker = new List<string>();


    if (this.openConnection() == true)
    {
        MySqlCommand cmd = new MySqlCommand(query, connection);
        //Een nieuw datareader object maken en dan query uitvoeren
        MySqlDataReader dataReader = cmd.ExecuteReader();


        while (dataReader.Read())
        {
            listGebruiker.Add(dataReader["id"].ToString());
            listGebruiker.Add(dataReader["voornaam"].ToString());
            listGebruiker.Add(dataReader["achternaam"].ToString());
            listGebruiker.Add(dataReader["geboortedatum"].ToString());
            listGebruiker.Add(dataReader["Rol_id"].ToString());
        }

        dataReader.Close();

        this.closeConnection();

        return list;
    }

and

    DBconnect connectDB = new DBconnect();
    List<string> persGegevens = connectDB.persoonlijkeGegevens(userId);

    lblVoornaamVrbl.Text = persGegevens[1];
    lblAchternaamVrbl.Text = persGegevens[2];
    lblGbrtedatumVrbl.Text = persGegevens[3];
    lblFuntieVrbl.Text = persGegevens[4];

Hope this helps

It might indeed be a better solution to not use a list<> array but to use list. I did not think about that because i was following a tutorial. Thanks.

nik0lai · Accepted Answer · 2016-05-26 13:01:39Z

2

You are trying to do a ToString() on a list, hence the output. You need to specify where in the array or list you want to display and do a ToString() on. The below will work or you could use another variable to loop through each user to get their details.

DBconnect connectDB = new DBconnect();
    List<string>[] persGegevens = connectDB.persoonlijkeGegevens(userId);
    for (int i = 0; i <= persGegevens.Count(); i++)
    {
        switch (i)
        {
            case 0:
                break;
            case 1:
                lblVoornaamVrbl.Text = persGegevens[i][0].ToString();
                break;
            case 2:
                lblAchternaamVrbl.Text = persGegevens[i][1].ToString();
                break;
            case 3:
                lblGbrtedatumVrbl.Text = persGegevens[i][2].ToString();
                break;
            case 4:
                lblFuntieVrbl.Text = persGegevens[i][3].ToString();
                break;
            default:
                break;
        }
    }

edited May 26, 2016 at 13:01

answered May 26, 2016 at 12:54

nik0lai

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1 Comment

Gertjan Brouwer Over a year ago

This indeed works, I use PersGegevens[i][0] because every list on list<string>[] only has 1 element. Thanks for the help.

apomene · Accepted Answer · 2016-05-26 12:53:52Z

1

persGegevens[i] is of type List<string>, so persGegevens[i].ToString() wont give anything meaningful. You need something like:

persGegevens[i][j];

answered May 26, 2016 at 12:53

apomene

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