2. 多对多关系

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
class HeroTeamLink(SQLModel, table=True):
    team_id: int | None = Field(default=None, foreign_key="team.id", primary_key=True)
    hero_id: int | None = Field(default=None, foreign_key="hero.id", primary_key=True)


class Team(SQLModel, table=True):
    id: int | None = Field(default=None, primary_key=True)
    name: str = Field(index=True)
    headquarters: str

    heroes: list["Hero"] = Relationship(back_populates="teams", link_model=HeroTeamLink)


class Hero(SQLModel, table=True):
    id: int | None = Field(default=None, primary_key=True)
    name: str = Field(index=True)
    secret_name: str
    age: int | None = Field(default=None, index=True)

    teams: list[Team] = Relationship(back_populates="heroes", link_model=HeroTeamLink)

多对多关系需要引入一张额外的中间表HeroTeamLink：

  • HeroTeamLink是一张中间表，所以其中不需要定义Relationship字段。
  • 中间表中只需要设置两个外键字段，并设置成联合主键

多对多关系中，两个实体类的定义基本相同，只要注意一下未定义类的引用即可：

1
heroes: list["Hero"] = Relationship(back_populates="teams", link_model=HeroTeamLink)

关系字段的定义跟一对多关系中父表中的定义基本类似，不过这里需要用link_model来指定中间表。

完整案例：

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
from sqlmodel import Field, Relationship, Session, SQLModel, create_engine


class HeroTeamLink(SQLModel, table=True):
    team_id: int | None = Field(default=None, foreign_key="team.id", primary_key=True)
    hero_id: int | None = Field(default=None, foreign_key="hero.id", primary_key=True)


class Team(SQLModel, table=True):
    id: int | None = Field(default=None, primary_key=True)
    name: str = Field(index=True)
    headquarters: str

    heroes: list["Hero"] = Relationship(back_populates="teams", link_model=HeroTeamLink)


class Hero(SQLModel, table=True):
    id: int | None = Field(default=None, primary_key=True)
    name: str = Field(index=True)
    secret_name: str
    age: int | None = Field(default=None, index=True)

    teams: list[Team] = Relationship(back_populates="heroes", link_model=HeroTeamLink)


def test():
    sqlite_file_name = "database.db"
    sqlite_url = f"sqlite:///{sqlite_file_name}"
    engine = create_engine(sqlite_url, echo=True)
    SQLModel.metadata.drop_all(engine)
    SQLModel.metadata.create_all(engine)

    with Session(engine) as session:
        team_preventers = Team(name="Preventers", headquarters="Sharp Tower")
        team_z_force = Team(name="Z-Force", headquarters="Sister Margaret's Bar")

        hero_deadpond = Hero(
            name="Deadpond",
            secret_name="Dive Wilson",
            teams=[team_z_force, team_preventers],
        )
        hero_rusty_man = Hero(
            name="Rusty-Man",
            secret_name="Tommy Sharp",
            age=48,
            teams=[team_preventers],
        )
        hero_spider_boy = Hero(
            name="Spider-Boy", secret_name="Pedro Parqueador", teams=[team_preventers],
        )
        session.add(hero_deadpond)
        session.add(hero_rusty_man)
        session.add(hero_spider_boy)
        session.commit()

        session.refresh(hero_deadpond)
        session.refresh(hero_rusty_man)
        session.refresh(hero_spider_boy)

        print("Deadpond:", hero_deadpond)
        print("Deadpond teams:", hero_deadpond.teams)
        print("Rusty-Man:", hero_rusty_man)
        print("Rusty-Man Teams:", hero_rusty_man.teams)
        print("Spider-Boy:", hero_spider_boy)
        print("Spider-Boy Teams:", hero_spider_boy.teams)


if __name__ == "__main__":
    test()