.NET Core - Targetting old .NET framework

Question

What I want to do: use an older project (.NET 3.5) data context and repositories in a .net core application (targetting .net 4.5). I put a more detailed explanation and what I tried below.

What I want to do

I am building a MVC application using .NET Core (on .NET 4.6 framework) at my work. The application needs to integrate with an existing database.

Normally in my .NET Core MVC applications, in startup.cs I do something like:

services.DbContext<Context>(options...) and parse a connection string. I then do services.AddTransient ... and inject a repository to my controllers, which lets me access the database.

However, instead of setting up my own database context and repositories and queries, I would like to use the existing codebase at my work. I created my project in the same solution as the existing ones. The existing projects are web forms, and use .NET 3.5. The way they do the database and repositories is a bit different - it uses DataContext in System.Data.Linq , and reads a connection string from web.config . Instead of dependency injection, then, the controllers just instantiate an instance of this class.

What I have tried

In my startup.cs , I tried to create a DataContext and parse it into the other project's repository, but it said something like You need to reference System.Data.Linq in the .NET framework 3.5.0 .

Is it possible for a .NET Core project targeting .NET 4.5, to use data context classes and repositories built using .NET 3.5?

Answer 1

I actually solved my problem. I don't think I was clear enough. Here is what my solution is like:

Solution - .NET 3.5 project - .NET 4.5 project

I was creating a repository from .NET 3.5 project in my newer one, and it was creating a datacontext that looks for a web.config file. Even though I created one, it looks like it must try to find that web.config inside of the startup project, regardless of where the data context is created. I made one but it still didn't detect that, I'm not sure why.

I was able to go into the old project and modify the datacontext to directly received a connection string. However, this isn't ideal - I will look for a way to pass a connection string into the older project from my new one, which I think is a good solution.

@jwdeny was correct in saying I had to add a reference to System.Data.Linq. The project told me to add a reference to 3.5, but adding System.Data.Linq 4.0 was enough.