Cannot Attach .mdf as Database

Emmmanuel FIADUFE

2y905C#

Hello Team,

Please in my window application, when I run my application set up this is the error I get, kindly assist.

I have my .mdf database in my App_Data folder, I testeted the connection string and is working but when I run the application sep up then the error popup

6 Replies

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Jignesh Kumar2y ago

Accepted answer

Hello EMMMANUEL,

This error seems your SQL server instance, username, and password. If any of these three, not correct please check these properties in your connection string and make it correct,

string connectionString = @"Data Source=(LocalDB)\MSSQLLocalDB;AttachDbFilename=|DataDirectory|\YourDatabase.mdf;Integrated Security=True";

string connectionString = @"Data Source=.;AttachDbFilename=|DataDirectory|\YourDatabase.mdf;Integrated Security=True";

Emmmanuel FIADUFE2y ago
Thank you team
Sam Hobbs2y ago
It depends on whether you are using Windows Authentication or SQL Server Authentication. A username and password is required for SQL Server Authentication but not Windows Authentication. See:

Choose an authentication mode - SQL Server | Microsoft Learn
https://learn.microsoft.com/en-us/sql/relational-databases/security/choose-an-authentication-mode?view=sql-server-ver16

Also, if you have not connected to the database using Visual Studio's Server Explorer and SQL Server Object Explorer then do that. They can be very helpful.

Connect to database or open MDF file (ADO.NET) - Visual Studio (Windows) | Microsoft Learn
https://learn.microsoft.com/en-us/visualstudio/data-tools/add-new-connections?view=vs-2022
Emmmanuel FIADUFE2y ago
Hello Kumar,

Please I did as you said but it didn't work
Emmmanuel FIADUFE2y ago
Hello Team,

After I successfully run the application and when I tried to save data this is the error I got, kindly assist,
Emmmanuel FIADUFE2y ago
Hello team,

I found the solution now,

I went to the file system and I created App_Data folder and loaded the .mdf database into it and it works for me.