List.Add方法不起作用

Question

public class abc
    {
        public abc(int ID, string Date, string jobtype, string command)
        {
            this.ID = ID;
            this.Date = Date;
            this.jobtype = jobtype;
            this.command = command;
        }

        public int ID { get; set; }
        public string Date { get; set; }
        public string jobtype { get; set; }
        public string command { get; set; }
    }

    public List<abc> getdata()
    {
        List<abc> data = new List<abc>();
        SqlCommand cmd = new SqlCommand("SELECT * FROM [Table]",connection1);
        using (connection1)
        {
            connection1.Open();
            using (SqlDataReader sdr = cmd.ExecuteReader())
            {
                while (sdr.Read())
                {
                    **data.Add(sdr["job_type"]);**
                }
                connection1.Close();
                return data;
            }
        }
    }

   private DataTable Getdata(SqlCommand cmd)

    {
        DataTable dt = new DataTable();
        SqlDataAdapter sda = new SqlDataAdapter();
        cmd.CommandType = CommandType.Text;
        cmd.Connection = connection1;

        try
        {
            connection1.Open();
            sda.SelectCommand = cmd;
            sda.Fill(dt);
            return dt;
        }

        catch
        {
            return null;
        }

        finally
        {
            connection1.Close();
            sda.Dispose();
            connection1.Dispose();
        }
    }

My code as above, I got an error on data.Add(sdr["job_type"]); where:

Error 2 The best overloaded method match for 'System.Collections.Generic.List has some invalid arguments Error 3 Argument 1: cannot convert from 'object' to 'WindowsFormsApplication1.Form1.abc'

I try to find some solutions through Google but no luck finding one. I quite new to C# so can anyone please tell me where I did wrong? The code are some example that I came across during searching.

Is there any alternative to the ways to place data from database in a list like shown above? Thanks.

Answer 1

You cannot simply cast your database object to your abc class. You will need to read each column and create a new abc object, as your list can only contain objects abc .

For example (I am doing this based on MySQLReader knowledge, it may be a bit different)

while (sdr.Read())
{
    data.Add(new abc((int)sdr["ID"],
    (string)sdr["Date"],
    (string)sdr["job_type"],
    (string)sdr["command"]));
}

Obviously the column names need to be renamed to your exact column names.

Answer 2

You would have to create a new abc object from the actual row you are reading from the Database.

Something like

data.Add(new abc(
    Convert.ToInt32(sdr["ID"]), 
    Convert.ToString(sdr["DATE"]), 
    Convert.ToString(sdr["job_type"]), 
    Convert.ToString(sdr["command"]))
    );

Answer 3

May be like this

You need to Specify Your Properties with Creating Object of Class

data.Add(new abc() {job_type1=sdr["job_type"].ToString()});

Or

Passing Data To Constructor Of Your Class Abc

data.Add(new abc(sdr["job_type"].ToString()));

For Reference

Go through MSDN

Answer 4

 using (SqlDataReader sdr = cmd.ExecuteReader())
            {
                abc temp = new abc();

                while (sdr.Read())
                {
                     temp = new abc();
                     temp.ID =  Convert.ToInt32(sdr["ID"]);
                      temp.Date =  Convert.ToDate(sdr["Date"]);
                       temp.jobtype =  Convert.ToString(sdr["job_type"]);
                     temp.command =  Convert.ToString(sdr["command"]);
                    data.Add(temp);
                }
                connection1.Close();
                return data;
            }

Answer 5

I suggest to modify the abc 's constructor so that it takes the SqlDataReader as a parameter and do the assignment work inside the constructor:

public class abc
{
    private enum Column
    {
        ID = 1,
        Date = 2,
        jobtype = 3,
        command = 4
    }

    public abc(SqlDataReader reader)
    {
        ID = sdr.GetFieldValue<int>[Column.ID];
        Date = sdr.GetFieldValue<string>[Column.Date];
        jobtype = sdr.GetFieldValue<string>[Column.jobtype];
        command = sdr.GetFieldValue<string>[Column.command];

        // or
        //ID = (int)sdr["ID"];
        //Date = (string)sdr["Date"];
        //jobtype =(string)sdr["jobtype"];
        //command = (string)sdr["command"];
    }

    public int ID { get; set; }
    public string Date { get; set; }
    public string jobtype { get; set; }
    public string command { get; set; }
}

this way your loop is nice and clean and the parsing/casting (if any) encapsulated:

while (sdr.Read())
{
    data.Add(new abc(sdr));
}