Question

I am new to MVC and dependency injection. Please help me to understand how that should work. I use Ninject. Here is my code:

in Global.asax file:

private void RegisterDependencyResolver()
    {
        var kernel = new StandardKernel();
        kernel.Bind<IDbAccessLayer>().To<DAL>(); 
        // DAL - is a Data Access Layer that comes from separated class library 
        DependencyResolver.SetResolver(new NinjectDependencyResolver(kernel));
    }

protected void Application_Start()
    {
        RegisterDependencyResolver();
    }

IDbAccessLayer implementation is very simple:

public interface IDbAccessLayer
{
  DataContext Data { get; }
  IEnumerable<User> GetUsers();
}

now in a Controller I need to create a constructor that gets IDbAccessLayer param. And that just works.

Now I don’t know how to pass a connection string to DAL. if I try to replace DAL’s constructor with something that accepts a parameter, it doesn’t work. Throws an exception with message No parameterless constructor defined for this object

Answer 1

You could specify constructor parameters:

kernel
    .Bind<IDbAccessLayer>()
    .To<DAL>()
    .WithConstructorArgument("connectionString", "YOUR CONNECTION STRING HERE");

And instead of hardcoding the connection string in your Global.asax you could read it from your web.config using:

ConfigurationManager.ConnectionStrings["CNName"].ConnectionString

and now your DAL class could take the connection string as parameter:

public class DAL: IDbAccessLayer
{
    private readonly string _connectionString;
    public DAL(string connectionString) 
    {
        _connectionString = connectionString;
    } 

    ... implementation of the IDbAccessLayer methods
}