Reading values from SQL database in C#

Question

i have just started learning C# and i can write data to the database without a problem. But i'm having problems with reading, the SQL executes fine but i'm having issues with storing it. How would i store the four columns that should be returned and then show them as a message box? Thanks.

SqlCommand myCommand = new SqlCommand("select * from Requests where Complete = 0", myConnection);
SqlDataReader myReader = myCommand.ExecuteReader();
while (myReader.Read())

Console.WriteLine(myReader["Username"].ToString());
Console.WriteLine(myReader["Item"].ToString());
Console.WriteLine(myReader["Amount"].ToString());
Console.WriteLine(myReader["Complete"].ToString());

Solution 1

One problem is missing braces after the while

while (myReader.Read())
{  // <<- here
    Console.WriteLine(myReader["Username"].ToString());
    Console.WriteLine(myReader["Item"].ToString());
    Console.WriteLine(myReader["Amount"].ToString());
    Console.WriteLine(myReader["Complete"].ToString());
}  // <<- here

if you skip the braces only the first line will be processed in each loop, the rest will be processed after the loop, then myReader is past the last row.

Solution 2

Don't forget to use the using(){} block :

using (SqlConnection connection = new SqlConnection(connectionString))
using (SqlCommand command = new SqlCommand("select * from Requests where Complete = 0", connection))
{
    connection.Open();  
    using (SqlDataReader reader = command.ExecuteReader())
    {
        while (reader.Read())
        {
            Console.WriteLine(reader["Username"].ToString());
            Console.WriteLine(reader["Item"].ToString());
            Console.WriteLine(reader["Amount"].ToString());
            Console.WriteLine(reader["Complete"].ToString());
        }
    }
}

Solution 3

Personally I'd write a class with 4 properties (with matching names and types), then use "dapper" (http://code.google.com/p/dapper-dot-net/):

var data = connection.Query<Request>(
    "select * from Requests where Complete = 0").ToList();

With something like:

public class Request {
    public string Username{get;set;}
    ...
    public bool Complete {get;set;}
}

Dapper is free, simple, has parameterisation to avoid SQL-injection, and is very very fast.

Comments

[Albin Sunnanbo]

When using databases in c# you should really have a look at Linq2SQL or Entity Framework. It simplifies a lot.

[Albin Sunnanbo]

@abatishchev Linq2Sql has helped me more often than not. The readability, compile time type checking and the intellisense really helps productivity in my experience.

[abatishchev]

@Albin: I agree that ORM is great technology but it isn't necessary to use it everywhere. On newbie level it will confuse more then teach

[TomTom]

On top the question has NOTHING to do with teh database but more with how to deal with the data after reading it. Poster is bviously challenged with beginner questions regarding programming.

[Matthew Cox]

@Paul if this answered your question, which appears to be the case, please be sure to mark the response as the answer. This is the check mark symbol by answer posts.

[Marc Gravell]

Never, ever, ever call a custom type Object :)