Exception connecting to SQL Server from c#

Question

i am working on a simple database project in c sharp and ms sql sever 2008 but im having an error upon compiling the program its poping up this message:

The type initializer for 'StudentsInformationSystem.DB_conection' threw an exception

My code:

namespace StudentsInformationSystem
{
    class DB_Access
    {
        private SqlConnection conn;

        public DB_Access()
        {
            conn = DB_conection.GetConnection(); //this is where i am getting the error on this line of code

        }

       public void add_student(string regNo,string fname, string lname, string phoneNo)
       {
            if (conn.State.ToString() == "closed")
            {
                conn.Open();
            }

            SqlCommand newCmd = conn.CreateCommand();
            newCmd.Connection = conn;
            newCmd.CommandType = CommandType.Text;
            newCmd.CommandText = "insert into student values('" + regNo + "','" + fname + "','" + lname + "','" + phoneNo + "')";
            newCmd.ExecuteNonQuery();
        }
    }
}

im a newbie mind explaining to me what you mean??like InnerException. — Mildred Shimz, Sep 16 '12 at 16:09
What error do you get? tell the error sentence please. Most likely it would be something like "connection is not open" is it so? — Sami, Sep 16 '12 at 16:14
what is db_connection called? i think you need to initialize DB_Connection instance. — VIRA, Sep 16 '12 at 16:15
@MildredShimz: *Exceptions* occur at execution time. If you're running the code, it must have *compiled* without error. Compile-time errors are the ones which show up in the Visual Studio "Errors" view, such as if you make a typo and try to use a variable which doesn't exist. — Jon Skeet, Sep 16 '12 at 16:15

score 3 · Answer 1 · answered Sep 16 '12 at 16:09

3

SQL Injection issues aside, your problem likely comes from comparing ConnectionState to a string.

/* this will never be true because "closed" is not equal to "Closed" */
if (conn.State.ToString() == "closed")
{
   conn.Open();
}

... should be:

if (conn.State == ConnectionState.Closed)
{
    conn.Open();
}

You should also get the connection as close to its usage as possible and never store it as a class-level variable.

using (var conn = DB_conection.GetConnection())
using (var cmd = conn.CreateCommand())
{
    // use conn & cmd

    // they will be closed & disposed of when they leave this block
}

answered Sep 16 '12 at 16:09

Austin Salonen

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its still giving me the same problem,i have edited it to show you where exactly im getting the error – Mildred Shimz Sep 16 '12 at 16:20
@MildredShimz: My answer is still valid for other issues you'll encounter. To adequately answer your question, you'll need to post the code for `DB_connection`. – Austin Salonen Sep 16 '12 at 18:16
As for actually having the `DB_connection` class at all, please see this answer: http://stackoverflow.com/a/9707060/4068 – Austin Salonen Sep 16 '12 at 18:17
im am reposting the question again – Mildred Shimz Sep 17 '12 at 10:57

score 0 · Answer 2 · answered Sep 16 '12 at 16:28

Supposing that there is no problem with your DB_conection (you have not shared it's details)

Few improvements in the code

public void add_student(string regNo,string fname, string lname, string phoneNo)
{
     if (conn.State == ConnectionSate.Closed)          
            conn.Open();         
     SqlCommand newCmd = conn.CreateCommand();
     newCmd.CommandText = "insert into student values('" + regNo + "','" + fname + "','" + lname + "','" + phoneNo + "')";
     newCmd.ExecuteNonQuery();
}

I will recommend to not close the connection after each query for the sake of quick accessibility of database, and you are already doing this. However after using a data-reader you should close the data-reader, otherwise it could cause some error

//newCmd.Connection = conn; No need you have done this in above statement

//newCmd.CommandType = CommandType.Text; No need, it is by default

score 0 · Answer 3 · answered Sep 16 '12 at 16:34

Type initializer for [class name] threw an exception.

This indicates an exception raised within the static constructor of a class. You need to check the static constructor of class DB_conection. Its code will be executed before the static method call GetConnection in the code you've shown.

If you run your code in a debugger I'm sure the source of the exception will be obvious.

score 0 · Answer 4 · edited Oct 06 '12 at 20:01

I dont know if you have fixed the problem since now , but if the application you a writing is from a youtube user tutorial ,

the problem is on the app.confing xml you write at first http://www.youtube.com/watch?list=UL53a-mKN01jQ&v=53a-mKN01jQ&feature=player_detailpage#t=479s

remove the <configSections></configSections>and leave <connectionStrings><add ..</connection Strings> and it should work

Exception connecting to SQL Server from c#

4 Answers4