Use of SQL DataReader in ForEach loop

bond007 · April 15th, 2009, 08:24 PM

hello everyone!!!

my problem is that,i hav extracted a whole column from a table through a SQL Command and stored it into a reader object.now i want to check each value of the column against a string.

Can i do it by using ForEach loop?if yes than plz tell me how. if not,than any other way to do this check???

thanks!!!

Lee Dumond · April 16th, 2009, 12:54 AM

To loop through a reader, you would generally use a while loop,

Code:

 
while (reader.Read())
{
   if (reader["MyColumn"].ToString() == stringToCompare)
   {
      // do something
   }
}

Remember, a reader provides forward-only access to its values. The Read() method evalutes to true if there are more records left to read, otherwise false. So once reader.Read() becomes false, the while loop would be terminated.

April 22nd, 2009, 06:05 AM

In C#, a DataSet uses a DataReader to populate itself. By definition, a DataReader is basic and efficient access method to access data and return result as they become available. A DataSet, on the other hand, has to wait for the entire query to process.
The Advantages of the DataReader Example of code:
SqlConnection sql= new SqlConnection(connectionString);
SqlDataAdapter a = new SqlDataAdapter
("select * from mytable;",sql);
DataSet ds = new DataSet();
a.Fill(ds);
foreach (DataRow dr in ds.Tables[0].Rows)
{
Console.WriteLine(dr[0].ToString());
}
The foreach loop does not begin until the DataSet is populated. This means any conditional checks or manipulations must occur in the query or after the DataSet is filled.

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