mdf文件的ASP.NET connectionString不起作用

Question

I am using I am using Visual Studio 2017. I just created a brand new mdf file in my project (Right click on App Data -> Add New Item -> SQL Server Database) and I called the file TestDatabase.mdf

Now I am trying to connect to it via a connection string:

<add name="TestConnection" connectionString="Server=.\SQLExpress;AttachDbFilename=|DataDirectory|TestDatabase.mdf;Database=TestDatabase; Trusted_Connection=Yes;" providerName="System.Data.SqlClient" />

Next I created a Model and then Created a EntityFramework Controller, but now when I goto the controller index method I get this error:

A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: SQL Network Interfaces, error: 26 - Error Locating Server/Instance Specified)

What am I doing wrong?

Answer 1

Make sure you testDatabase.mdf available in App_Data folder.

<connectionStrings>
  <add name="ConnectionName"
    connectionString="Data Source=.\SQLEXPRESS;AttachDbFilename=|DataDirectory|DatabaseName.mdf;Integrated Security=True;User Instance=True"
    providerName="System.Data.SqlClient" />
</connectionStrings>

Answer 2

This connection string that you have written is incorrect.

<add name="TestConnection" connectionString="Server=.\SQLExpress;AttachDbFilename=|DataDirectory|TestDatabase.mdf;Database=TestDatabase; Trusted_Connection=Yes;" providerName="System.Data.SqlClient" />

I assume that you have SQL Express installed in your system. This will provide a local instance of SQL to run on your machine.

As you said you are using Visual Studio 2017, you can follow these steps to get the correct connection string

1. Open Server Explorer
2. Right Click on your Database and click Properties

3. A property window will open, copy the ConnectionString and make sure it looks like this:

   <add name="YourDbName" connectionString="Data Source=YourComputerName\\SQLEXPRESS;Initial Catalog=YourDbName;Integrated Security=True" />

And now talking about this:

A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: SQL Network Interfaces, error: 26 - Error Locating Server/Instance Specified)

You are getting this error because it is not getting the instance name to connect to the database. In my example, SQLEXPRESS serves as an instance name. If you don't have SQLEXPRESS you can download it from here: https://www.microsoft.com/en-in/sql-server/sql-server-editions-express You can follow the prompt and install this package in your system.

Once you install this, your instance will get activated. Connect your Db once again.I am sure it will work.

In case, if this error comes again, you can follow these steps:

1. Hit Windows + R and type services.msc and hit OK
2. From the given lists, search for SqlServer (SQLEXPRESS) and click start the service . This will activate your instance once again and your database is now ready to connect to your application.

Hope this helps.