This is a very simple question...
I have reverse engineered an existing database with entity framework core, it works well and I have my classes defined, it has also created on the OnModelCreating event thousands and thousands of line of code detailing all the indexes references etc...
Do I need this code? I am not planning to modify the db schema just simply reading data and updating data from an api, can I comment out all of these lines?
You mean protected override void OnModelCreating(ModelBuilder modelBuilder) method in you DbContext class?
Yes, you need it.
It contains description of references between your entities - it's important for EF to build correct SQL queries.
It is possible to optimize/minimize it (by removing some lines that do not important for your area), but it's manual operation, if you have enough time...