I'm currently attempting to connect to a local copy of a database for testing purposes as to not alter live data.

I'm using MVC with Entity Framework (.Net 4.5), and I'm currently running into this error whenever I attempt to access data through EF:

An exception of type 'System.Data.EntityException' occurred in System.Data.Entity.dll but was not handled in user code

Additional information: The underlying provider failed on Open.

This is the function that is trying to access the data - the error happens on the first line

public IEnumerable<Client> GetClients()
{
    List<Client> clients = (from c in this.repository.Clients select c).ToList();
    return clients;
}

Here is my connection string in the app.config as well:

<add name="EntitiesConnectionString" connectionString="metadata=res://*/EFName.csdl|res://*/EFName.ssdl|res://*/EFName.msl;provider=System.Data.SqlClient;provider connection string="Data Source=(LocalDb)\v11.0;Initial Catalog=testdb;Integrated Security=True;Pooling=False"" providerName="System.Data.EntityClient" />

I'm using the integrated SQL Server Express that comes with Visual Studio 2015 to manage the local DB that I have created.

More information that I've found:

"Cannot open database \"testdb\" requested by the login. The login failed.\r\nLogin failed for user 'NT AUTHORITY\\SYSTEM'."

I don't believe that I have any permissions set on the db that I created, perhaps something is wrong with the connection string?

Edit:

I've added the 'NT AUTHORITY\NETWORK SERVICE' user, and then added it to the 'db_owner' role in MS SQL Server Management Studio without any luck

I also attempted to create a new login and user with credentials and the 'db_owner' role, and I still receive the same "Login failed for user 'user'."

This is the connection string that I'm using with the test user that I created:

<add name="EntitiesConnectionString" connectionString="metadata=res://*/EFName.csdl|res://*/EFName.ssdl|res://*/EFName.msl;provider=System.Data.SqlClient;provider connection string="Data Source=(LocalDb)\v11.0;Initial Catalog=testdb;Integrated Security=False;Persist Security Info=True;User ID=test;Password=password"" providerName="System.Data.EntityClient" />

You are likely enumerating GetClients() after disposing of the underlying connection.

Try either:

a) changing the return type of the method to something like List< Client>

public List<Client> GetClients()
{
    List<Client> clients = (from c in this.repository.Clients select c).ToList();
    return clients;
}

or b) call .ToList() on the method immediately:

IEnumerable<Clients> clients = GetClients().ToList();

As it is, execution of .ToList() inside your method is deferred until the method's return value is enumerated, which if I had to guess, is after the db connection has been disposed.