Python sqlalchemy同一个表的多个外键
我有一个postgres数据库,看起来像这样:Python sqlalchemy同一个表的多个外键,python,postgresql,sqlalchemy,flask-sqlalchemy,Python,Postgresql,Sqlalchemy,Flask Sqlalchemy,我有一个postgres数据库,看起来像这样: Table "public.entities" Column | Type | Modifiers ---------------+-----------------------------+------------------------------------------------ id
Table "public.entities"
Column | Type | Modifiers
---------------+-----------------------------+------------------------------------------------
id | bigint | not null default nextval('guid_seq'::regclass)
type_id | smallint | not null
name | character varying |
Indexes:
"entities_pkey" PRIMARY KEY, btree (id)
Foreign-key constraints:
"entities_parent_id_fkey" FOREIGN KEY (parent_id) REFERENCES entities(id)
"entities_type_id_fkey" FOREIGN KEY (type_id) REFERENCES entity_types(id)
Referenced by:
TABLE "posts" CONSTRAINT "posts_id_fkey" FOREIGN KEY (id) REFERENCES entities(id)
TABLE "posts" CONSTRAINT "posts_subject_1_fkey" FOREIGN KEY (subject_1) REFERENCES entities(id)
TABLE "posts" CONSTRAINT "posts_subject_2_fkey" FOREIGN KEY (subject_2) REFERENCES entities(id)
Table "public.posts"
Column | Type | Modifiers
-----------+--------+-----------
id | bigint | not null
poster_id | bigint |
subject_1 | bigint | not null
subject_2 | bigint | not null
Indexes:
"posts_pkey" PRIMARY KEY, btree (id)
Foreign-key constraints:
"posts_id_fkey" FOREIGN KEY (id) REFERENCES entities(id)
"posts_poster_id_fkey" FOREIGN KEY (poster_id) REFERENCES users(id)
"posts_subject_1_fkey" FOREIGN KEY (subject_1) REFERENCES entities(id)
"posts_subject_2_fkey" FOREIGN KEY (subject_2) REFERENCES entities(id)
我试图弄清楚如何为“posts”定义orm对象,以包含所有3个外键。请注意,只有id是主键。其他的只是帖子和实体之间的关系,不需要pk
class PostModel(EntitiesModel):
__tablename__ = 'posts'
id = db.Column(db.BigInteger, db.ForeignKey(EntitiesModel.id), primary_key=True, nullable=False)
poster_id = db.Column(db.BigInteger, db.ForeignKey(UserModel.id), nullable=False)
subject_1 = db.Column(db.BigInteger, db.ForeignKey(EntitiesModel.id), nullable=False)
subject_2 = db.Column(db.BigInteger, db.ForeignKey(EntitiesModel.id), nullable=False)
我试过稍微修改一下,除了禁用subject_1上的外键外,我似乎无法想出一个不会导致此错误的解决方案:
AmbiguousForeignKeysError: Can't determine join between 'entities' and 'posts'; tables have more than one foreign key constraint relationship between them. Please specify the 'onclause' of this join explicitly.
有什么想法吗?由于您忽略了最重要的部分,即引发该异常的代码,但如果将关系属性添加到类PostModel中,则会尝试将foreign_keys参数添加到关系调用中,如下所示:
class PostModel(...):
# ...
subject1_id = Column(db.Column(db.BigInteger, db.ForeignKey(EntitiesModel.id), nullable=False)
subject2_id = Column(db.Column(db.BigInteger, db.ForeignKey(EntitiesModel.id), nullable=False)
subject1 = relationship(EntitiesModel, foreign_keys=subject1_id)
subject2 = relationship(EntitiesModel, foreign_keys=subject2_id)