The EF Core code base is open source and contains several database providers that can be used as a reference. You can find the source code at https://github.com/aspnet/EntityFramework.
The providers-beware label
Once you begin work on a provider, watch for the
providers-beware label on our GitHub issues and pull requests. We use this label to identify changes that may impact provider writers.
Suggested naming of third party providers
We suggest using the following naming for NuGet packages. This is consistent with the names of packages delivered by the EF Core team.
<Optional project/company name>.EntityFrameworkCore.<Database engine name>