I have the situation
a model called contract and a model called parts,

a contract can have and be lrelated to many parts

i have the folowing Schema

Contract
-> title
-> start_date
-> due_date
-> file

Part
-> first_name
-> last_name
-> email
-> cpf
-> phone

ContractPart
-> contract_id
-> part_id

So how i can make a nested form to create those relationship between models?
exemple: i have a contract, A and a part B, C
so i want to related part B,C to contract A

but i havent any ideia how i can make a nested_form with a select to create this association