Maybe you could look into something that does the importing for you - there are SaaS providers now that will do this (I hear podcast ads about them sometimes... https://flatfile.com/platform/data-onboarding/ springs to mind). Source: about 2 years ago

For the simplicity we will use MSSQLProvider to fetch the data from the database. This class has basic functionality, if you want to create complex database queries, for example JOIN, you'd better use something like Entity Framework. - Source: dev.to / about 1 month ago

I only wanted to give a simple preview of what can be done with Entity Framework, but if this is something that interests you and you want to go further in-depth with all the possibilities, I recommend checking out the official docs where you can also find a great tutorial which will guide you through building your very own .NET Core web application. - Source: dev.to / about 1 year ago

Entity Framework documentation hub - Entity Framework is a modern object-relation mapper that lets you build a clean, portable, and high-level data access layer with .NET (C#) across a variety of databases, including SQL Database (on-premises and Azure), SQLite, MySQL, PostgreSQL, and Azure Cosmos DB. It supports LINQ queries, change tracking, updates, and schema migrations. Source: 12 months ago

You can create the DAL using your existing code or start using a Object Relational Mapper like Entity Framework which will do a lot of the work for you, check this out here: https://learn.microsoft.com/en-us/ef/ also check out LINQ. Source: about 1 year ago

And, possibly (not strictly speaking necessary but very useful) Entity framework as a backend part of it. Source: about 1 year ago