Inserting seeds from txt files

Suppose I have seeds, for pre-populating a database, of: countries and currencies, products, blog-articles, etc. I want to extract each of them into a separate file so that I can read it from seed.eex and insert data into my db. How would you recommend doing this?

What format of a file: yml, json, anything else?

How should I deal with the “belongs_to”, “has_many” cases in that text file? That is, how should I represent a seed and its parent or child seed together? It’ll require knowing a foreign id – you know what I mean.

That’s it for now.