[Django] 다대다 관계의 모델을 직접 활용해 보자

다대다 관계의 모델을 직접 활용해보자

1. 다대다 관계에서 모델 인스턴스 생성하기

1.객체 생성 후 save() 하기

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In [4]: person = Person.objects.create(name='권태형')
INSERT INTO "person" ("name")
VALUES ('권태형')
​
Execution time: 0.002013s [Database: default]
​
In [5]: python_group = Group.objects.create(name='파이썬모임')
INSERT INTO "group" ("name")
VALUES ('파이썬모임')
​
Execution time: 0.002968s [Database: default]
​
In [6]: vegeterian_group = Group.objects.create(name='채식모임')
INSERT INTO "group" ("name")
VALUES ('채식모임')
​
Execution time: 0.001940s [Database: default]
​
In [7]: m1 = Membership(person=person, group=python_group, sub_group=vegeterian_group, date_joined='2020-01-01', invite_reaso
   ...: n="그냥")
​
In [8]: m1.save()
INSERT INTO "membership" ("person_id", "group_id", "sub_group_id", "date_joined", "invite_reason")
VALUES (2, 3, 4, '2020-01-01', '그냥')
​

2..create 사용하기

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In [19]: person_2 = Person.objects.create(name='권태형2')
INSERT INTO "person" ("name")
VALUES ('권태형2')
​
Execution time: 0.001893s [Database: default]
​
In [20]: Membership.objects.create(group=vegeterian_group, sub_group=python_group, person=person_2, invite_reason="그냥", dat
    ...: e_joined='2020-01-01')
INSERT INTO "membership" ("person_id", "group_id", "sub_group_id", "date_joined", "invite_reason")
VALUES (3, 4, 3, '2020-01-01', '그냥')
​
Execution time: 0.001983s [Database: default]
Out[20]: <Membership: Membership object (2)>
​

 

2. through_defaults를 지정하여서, add() 사용하기

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# python_group이라는 그룹에 멤버를 추가할 때, Person 인스턴스를 넘겨주면 되는데, 이때 멤버쉽의 나머지 필드들은 through_fields에 정의해줄 수 있다
In [32]: python_group.members.add(python_man, through_defaults={'date_joined': '2020-01-01', 'sub_group': vegeterian_group})
BEGIN
​
Execution time: 0.000040s [Database: default]
SELECT "membership"."person_id"
  FROM "membership"
 WHERE ("membership"."group_id" = 3 AND "membership"."person_id" IN (4))
​
Execution time: 0.000108s [Database: default]
INSERT INTO "membership" ("person_id", "group_id", "sub_group_id", "date_joined", "invite_reason") SELECT 4,
       3,
       4,
       '2020-01-01',
       ''
​
Execution time: 0.000415s [Database: default]
​
In [33]: python_group.members.all()
Out[33]: SELECT "person"."id",
       "person"."name"
  FROM "person"
 INNER JOIN "membership"
    ON ("person"."id" = "membership"."person_id")
 WHERE "membership"."group_id" = 3
 LIMIT 21
​
Execution time: 0.000136s [Database: default]
<QuerySet [<Person: 권태형>, <Person: 파이썬맨>]>
​

 

3. remove()

remove를 사용하면 넘어오는 인스턴스에 해당하는 모든 값을 삭제한다.

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In [39]: python_group.members.all()
Out[39]: SELECT "person"."id",
       "person"."name"
  FROM "person"
 INNER JOIN "membership"
    ON ("person"."id" = "membership"."person_id")
 WHERE "membership"."group_id" = 3
 LIMIT 21
​
Execution time: 0.000118s [Database: default]
<QuerySet [<Person: 권태형>, <Person: 파이썬맨>, <Person: 권태형2>, <Person: 권태형2>]>
​
In [40]: person_2
Out[40]: <Person: 권태형2>
​
In [41]: python_group.members.remove(person_2)
BEGIN
​
Execution time: 0.000051s [Database: default]
DELETE
  FROM "membership"
 WHERE ("membership"."group_id" = 3 AND "membership"."person_id" IN (3))
​
Execution time: 0.000586s [Database: default]
​
In [42]: python_group.members.all()
Out[42]: SELECT "person"."id",
       "person"."name"
  FROM "person"
 INNER JOIN "membership"
    ON ("person"."id" = "membership"."person_id")
 WHERE "membership"."group_id" = 3
 LIMIT 21
​
Execution time: 0.000163s [Database: default]
<QuerySet [<Person: 권태형>, <Person: 파이썬맨>]>
​

 

4. clear()

깔끔하게 밀고 싶을 땐(?) clear를 사용하자.

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In [43]: python_group.members.all()
Out[43]: SELECT "person"."id",
       "person"."name"
  FROM "person"
 INNER JOIN "membership"
    ON ("person"."id" = "membership"."person_id")
 WHERE "membership"."group_id" = 3
 LIMIT 21
​
Execution time: 0.000120s [Database: default]
<QuerySet [<Person: 권태형>, <Person: 파이썬맨>]>
​
In [44]: python_group.members.clear()
BEGIN
​
Execution time: 0.000045s [Database: default]
DELETE
  FROM "membership"
 WHERE "membership"."group_id" = 3
​
Execution time: 0.000570s [Database: default]
​
In [45]: python_group.members.all()
Out[45]: SELECT "person"."id",
       "person"."name"
  FROM "person"
 INNER JOIN "membership"
    ON ("person"."id" = "membership"."person_id")
 WHERE "membership"."group_id" = 3
 LIMIT 21
​
Execution time: 0.000131s [Database: default]
<QuerySet []>
​