Visual Studio 2015附加SQL Server数据库文件失败求助

Got it, that error is super common when dealing with attached SQL Server files in VS—let's walk through the most likely fixes since you've already moved the offline file to your project folder:

• Check your SQL Server login's default database status
  This is the #1 culprit for this error. Here's how to fix it:

  1. Open SQL Server Management Studio (SSMS) and connect to your SQL Server instance.
  2. Expand Security > Logins, then find the account you're using to connect (either your Windows user or a SQL Server account).
  3. Right-click the login, select Properties, then go to the General tab.
  4. Make sure the Default database is set to a database that actually exists and is online (like master if your original default database is missing/offline).
  5. Save the changes, restart the SQL Server service, then try attaching the file again in VS.

• Fix file permissions for your .mdf/.ldf files
  Even if you moved the files to your project folder, SQL Server might not have access to them:

  1. Navigate to your project folder where the .mdf and .ldf files are stored.
  2. Right-click the files, select Properties > Security tab.
  3. Check if the SQL Server service account (usually NT SERVICE\MSSQLSERVER for default instances, or NT SERVICE\MSSQL$<YourInstanceName> for named instances) has Read & Write permissions.
  4. If it's not listed, click Edit > Add, type the account name, and grant the necessary permissions. Save your changes before retrying.

• Attach the database via SSMS first, then connect in VS
  Sometimes attaching directly through VS can hit permission snags—try doing it manually in SSMS:

  1. Open SSMS, right-click Databases > Attach.
  2. Click Add and select your .mdf file. If you get a permission warning here, follow the prompt to fix it.
  3. Once the database is attached successfully, go back to Visual Studio and connect to the already-attached database (instead of trying to attach the file directly).

• Verify your VS connection string
  If you're using a connection string in your project, double-check these details:

  • Ensure AttachDbFilename points to the correct path (use |DataDirectory|\YourDbName.mdf if the file is in your App_Data folder, or an absolute path if it's elsewhere).
  • For LocalDB instances, make sure your data source is correct (like (LocalDB)\MSSQLLocalDB).
  • Example valid connection string for Windows auth:

    Data Source=(LocalDB)\MSSQLLocalDB;AttachDbFilename=|DataDirectory|\MyDatabase.mdf;Integrated Security=True
    

内容的提问来源于stack exchange，提问作者doria_aries