error in Connection String in C#

Question

I am new to C#. I want to use my Microsoft SQL Server database file test.mdf in my output software in C#. In the past, I had just copied the connection string in Visual Studio like this :

Data Source=.\SQLEXPRESS;AttachDbFilename=C:\Users\Home\Documents\test.mdf;Integrated Security=True;Connect Timeout=30;User Instance=True

as you see the database file path is : C:\Users\Home\Documents\test.mdf;

When I create setup for my sofware in Visual Studio 2008, and install the software on another PC, it errors :

An attempt to atach an auto-named database for file C:\User\Home\Document\test.mdf failed ...

So I want to address the file with the installation folder path whith this :

string dir = Application.StartupPath + "\\" + "test.mdf";

but when I want to run program in Visual Studio 2008 it erros

string dir = Application.StartupPath + "\\" + "test.mdf";
SqlConnection con = new SqlConnection(@"Data Source=.\SQLEXPRESS;AttachDbFilename=" + dir + ";Integrated Security=True;Connect Timeout=30;User Instance=True");

Error 1 A field initializer cannot reference the non-static field, method, or property 'phonebook.Form1.dir' C:\Users\Home\Documents\Visual Studio 2008\Projects\phonebook\phonebook\Form1.cs 25 95 phonebook

UPDATE

When I use

 SqlConnection con = new SqlConnection(@"Data Source=.\SQLEXPRESS;AttachDbFilename="+ Application.StartupPath +" \\test.mdf;Integrated Security=True;Connect Timeout=30;User Instance=True");

it errors :

One or more files do not match the primary file of the database. If you are attempting to attach a database, retry the operation with the correct files. If this is an existing database, the file may be corrupted and should be restored from a backup. Cannot open user default database. Login failed. Login failed for user 'Home-PC\Home'.

While I have copied right test.mdf file there

try using a relative path instead, like ".\\test.mdf" if the file is in the program root. — Thorarins
– Thorarins, Commented Jul 8, 2015 at 8:05
Apart from fixing your error I suggest you use SqlConnectionStringBuilder to create your connection strings to avoid getting invalid values. — Thorsten Dittmar
– Thorsten Dittmar, Commented Jul 8, 2015 at 8:06
@Thorarins this does not work : [code]SqlConnection con = new SqlConnection(@"Data Source=.\SQLEXPRESS;AttachDbFilename=./test.mdf;Integrated Security=True;Connect Timeout=30;User Instance=True");[/code] — SoheilYou
– SoheilYou, Commented Jul 8, 2015 at 9:12
also this : SqlConnection con = new SqlConnection(@"Data Source=.\SQLEXPRESS;AttachDbFilename=.\test.mdf;Integrated Security=True;Connect Timeout=30;User Instance=True"); — SoheilYou
– SoheilYou, Commented Jul 8, 2015 at 9:14

Jon Skeet · Accepted Answer · 2015-07-08 08:04:34Z

3

As the error message says, you can't use the value of one instance field when initializing another. You probably don't want dir as a field anyway. Just move all of this into the body of the constructor... or ideally, only create your SqlConnection when you need it anyway. Don't use a single instance throughout your application, but go through a "create, use, dispose" cycle every time you need database access. (Ideally, don't do this in your GUI code, either...)

answered Jul 8, 2015 at 8:04

Jon Skeet

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9 Comments

SoheilYou Over a year ago

I could not solve my problem . would you plz give me a relative right code ?

Jon Skeet Over a year ago

@soheilyo: No - you've given no indication how you tried to apply my answer, or what problems you ran into. Stack Overflow isn't a "gimme teh codez" site. I've suggested a fairly significant change to your code, within the answer (creating a SqlConnection only when you need to, and disposing it immediately after use) - have you tried implementing that?

Thorarins Over a year ago

problem is also solved here stackoverflow.com/questions/3500829/…

Jon Skeet Over a year ago

@Thorarins: No, that's a different problem. The OP is running into a compile-time error which doesn't occur in that question.

Thorarins Over a year ago

@Jon yes, but his main problem is the connection string which they solved in the answers I posted so probably it will help to solve his problem

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