The Seed method runs every time the application starts, so the way you have coded it will attempt to add the FoodWeight
s over and over again. EF have provided the AddOrUpdate
as a convenient method to prevent that but it is really not appropriate for bulk inserts.
You could use sql directly on the database - and if you are using sql server that sql could be 'BULK INSERT'.
I would put the sql in an Up migration because you probably only want to run the insert once from a known state, and it avoids having to worry about the efficiency of the context and tracking changes etc.
There is example code and more information here: how to seed data using sql files