How do I loop through rows with a data reader in C#?

I know I can use while(dr.Read()){...} but that loops every field on my table, I want to retrieve all the values from the first row, and then second… and so on.

Let’s say I have a table like this:

ID--------------Value1--------------Value2------------------Value3
1               hello               hello2                  hello3
2               hi1                  hi2                      hi3

first I want to get, hello, hello2 and hello3 and then go to the second row and get all the values.

Is there a way to achieve this? I hope somebody understand what I mean.

I am so sorry, this is solved now. I just wasn’t coding right…

And yeah the SqlDataReader.Read() method does what it is supposed to do, again the mistake was mine.

Answers:

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Method 1

That’s the way the DataReader works, it’s designed to read the database rows one at a time.

while(reader.Read()) 
{
  var value1 = reader.GetValue(0); // On first iteration will be hello
  var value2 = reader.GetValue(1); // On first iteration will be hello2
  var value3 = reader.GetValue(2); // On first iteration will be hello3
}

Method 2

int count = reader.FieldCount;
while(reader.Read()) {
    for(int i = 0 ; i < count ; i++) {
        Console.WriteLine(reader.GetValue(i));
    }
}

Note; if you have multiple grids, then:

do {
    int count = reader.FieldCount;
    while(reader.Read()) {
        for(int i = 0 ; i < count ; i++) {
            Console.WriteLine(reader.GetValue(i));
        }
    }
} while (reader.NextResult())

Method 3

Or you can try to access the columns directly by name:

while(dr.Read())
{
    string col1 = (string)dr["Value1"];
    string col2 = (string)dr["Value2"];
    string col3 = (string)dr["Value3"];
}

Method 4

There is no way to get “the whole row” at once – you need to loop through the rows, and for each row, you need to read each column separately:

using(SqlDataReader rdr = cmd.ExecuteReader())
{
    while (rdr.Read())
    {
        string value1 = rdr.GetString(0);
        string value2 = rdr.GetString(1);
        string value3 = rdr.GetString(2);
    }
}

What you do with those strings that you read for each row is entirely up to you – you could store them into a class that you’ve defined, or whatever….

Method 5

How do I loop through rows with a data reader in C#?

IDataReader.Read() advances the reader to the next row in the resultset.

while(reader.Read()){
    /* do whatever you'd like to do for each row. */
}

So, for each iteration of your loop, you’d do another loop, 0 to reader.FieldCount, and call reader.GetValue(i) for each field.

The bigger question is what kind of structure do you want to use to hold that data?

Method 6

Actually the Read method iterating over records in a result set. In your case – over table rows. So you still can use it.

Method 7

while (dr.Read())
{
    for (int i = 0; i < dr.FieldCount; i++)
    {
        subjob.Items.Add(dr[i]);
    }
}

to read rows in one colunmn

Method 8

Suppose your DataTable has the following columns try this code:

DataTable dt =new DataTable();
txtTGrossWt.Text = dt.Compute("sum(fldGrossWeight)", "").ToString() == "" ? "0" : dt.Compute("sum(fldGrossWeight)", "").ToString();
txtTOtherWt.Text = dt.Compute("sum(fldOtherWeight)", "").ToString() == "" ? "0" : dt.Compute("sum(fldOtherWeight)", "").ToString();
txtTNetWt.Text = dt.Compute("sum(fldNetWeight)", "").ToString() == "" ? "0" : dt.Compute("sum(fldNetWeight)", "").ToString();
txtFinalValue.Text = dt.Compute("sum(fldValue)", "").ToString() == "" ? "0" : dt.Compute("sum(fldValue)", "").ToString();

All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0