Is there a way to turn a many to many object relationship into a dictionary?

Question

I have two classes

Club with property id and name
Student with property id, name and clubs (list)

One student can be part of multiple clubs.
One club can have multiple students

class Club:
 def __init__(self, id, name):
    self.id = id
    self.name = name

class Student:
 def __init__(self, id, name, clubs):
    self.id = id
    self.name = name
    self.clubs = clubs

I want to have a dictionary where the key is club name and value is list of students.

I have around 30 different many to many relationships in the application.

Is there a way to do it in a generic way?

Does this answer your question? [Object of custom type as dictionary key](https://stackoverflow.com/questions/4901815/object-of-custom-type-as-dictionary-key) — buran, Nov 07 '20 at 14:56
In addition to the link I provided it may be useful to have an attribute of `Club` that will hold all members. You can also add methods that will add club to student's clubs when added as club member as vice versa - add student to club members when club added to student's clubs — buran, Nov 07 '20 at 14:59
On a second reading - if the key is the club name, not the club instance - that's possible given that club names are unique. It maybe better to have club ids as keys — buran, Nov 07 '20 at 15:04

score 0 · Answer 1 · answered Nov 08 '20 at 11:49

A crude inverter could be like below.

def reverse(elems, array_name, i_key):
  dic = {}
  for elem in elems:
    for elem_field in elem[array_name]:
      key = elem_field[i_key]
      if key not in dic:
        dic[key] = []
      dic[key].append(elem)
  return dic

club_a = { 'name': 'a'}
club_b = { 'name': 'b'}
club_c = { 'name': 'c'}
stud_a = { 'id': 1, 'clubs': [club_a, club_b]}
stud_b = { 'id': 2, 'clubs': [club_b, club_c]}
print(reverse([stud_a, stud_b], 'clubs', 'name'))
# a: stud_a
# b: stud_a, stud_b
# c: stud_b

Is there a way to turn a many to many object relationship into a dictionary?

1 Answers1