ExecuteReader: Connection property has not been initialized. How to fix this?

Question

int tempid,temp1,temp2,temp3,temp4,temp5,temp6;
{
    SqlCommand cmd = new SqlCommand("select * from Szelvenyek");
    SqlConnection cn = new SqlConnection(@"Data Source=.\SQLEXPRESS;AttachDbFilename=D:\Iskola\C#\lotto_kerekeshunor\lotto_kerekeshunor\Database1.mdf;Integrated Security=True;User Instance=True");
    cn.Open();
    SqlDataReader dr = cmd.ExecuteReader();
    while (dr.Read())
    {
        tempid = (int)dr["ID"];
        temp1 = (int)dr["elso"];
        temp2 = (int)dr["masodik"];
        temp3 = (int)dr["harmadik"];
        temp4 = (int)dr["negyedik"];
        temp5 = (int)dr["otodik"];
        temp6 = (int)dr["hatodik"];

        if (r1 == temp1 || r1 == temp2 || r1 == temp3 || r1 == temp4 || r1 == temp5 || r1 == temp6) talalat[tempid]++;
        if (r2 == temp1 || r2 == temp2 || r2 == temp3 || r2 == temp4 || r2 == temp5 || r2 == temp6) talalat[tempid]++;
        if (r3 == temp1 || r3 == temp2 || r3 == temp3 || r3 == temp4 || r3 == temp5 || r3 == temp6) talalat[tempid]++;
        if (r4 == temp1 || r4 == temp2 || r4 == temp3 || r4 == temp4 || r4 == temp5 || r4 == temp6) talalat[tempid]++;
        if (r5 == temp1 || r5 == temp2 || r5 == temp3 || r5 == temp4 || r5 == temp5 || r5 == temp6) talalat[tempid]++;
        if (r6 == temp1 || r6 == temp2 || r6 == temp3 || r6 == temp4 || r6 == temp5 || r6 == temp6) talalat[tempid]++;
    }
}

I have this code, I want to read datas from database then compare them. Visual Basic says

"ExecuteReader: Connection property has not been initialized."

Any help?

Answer 1

Looks like you didn't initialize your SqlCommand.Connection property. Without this, your program can't know to execute your SqlCommand using which SqlConnection. Just add;

cmd.Connection = cn;
cn.Open();
...

Or you can pass your SqlConnection to your SqlCommand constructor as a second parameter (which I always prefer) like;

SqlCommand cmd = new SqlCommand("select * from Szelvenyek", cn);

Also use using statement to dispose your SqlConnection, SqlCommand and SqlDataReader like;

using(SqlConnection cn = new SqlConnection(@"Data Source=.\SQLEXPRESS;AttachDbFilename=D:\Iskola\C#\lotto_kerekeshunor\lotto_kerekeshunor\Database1.mdf;Integrated Security=True;User Instance=True"))
using(SqlCommand cmd = new SqlCommand("select * from Szelvenyek", cn))
{
   cn.Open();
   using(SqlDataReader dr = cmd.ExecuteReader())
   {
      while(dr.Read())
      {
         ///
      }
   }
}

Answer 2

It's easy to forget this. You can set the property by hand, or you can make it a habit to construct commands after your connection, so you can pass it to the constructor:

SqlConnection cn = new SqlConnection(@"Data Source=.\SQLEXPRESS;AttachDbFilename=D:\Iskola\C#\lotto_kerekeshunor\lotto_kerekeshunor\Database1.mdf;Integrated Security=True;User Instance=True");

SqlCommand cmd = new SqlCommand("select * from Szelvenyek", cn);