Flask-SQLAlchemy 如何存儲 ForeignKey 對象列表

Question

我正在創建一個應用程序，它將收集許多不同“類型”項目的要求，但無法弄清楚如何構建 Flask-SQLAlchemy ORM Model 關系。

我有以下課程：

ItemSize - 一個“類型”，比如 T 恤尺寸。

class ItemSize(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(80), unique=True, nullable=False)
    date_created = db.Column(db.Date(), default=datetime.now())
    height = db.Column(db.Integer, nullable=True)
    depth = db.Column(db.Integer, nullable=True)
    width = db.Column(db.Integer, nullable=True)

ItemSet - 特定 ItemSize 的集合，存儲與 ItemSize 和 Count 的關系。 （例如，ItemSize：'A'，計數：2）

class ItemSet(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    size = db.Column(db.Integer, db.ForeignKey('itemsizes.id'), nullable=True)
    count = db.Column(db.Integer, nullable=False)

要求 - 許多 ItemSet 的集合。 （例如，ItemSets [1, 2, 3, 4, 5]）

class Specification(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(80), unique=True, nullable=False)
    comments = db.Column(db.String(255), nullable=True)
    
    # THIS IS THE BIT I AM UNSURE OF
    # Need this to a collection of Many ItemSets
    # Will the below work? 
    requirements = db.relationship('ItemSet', uselist=True, backref='itemsets')    

以上在嘗試創建任何對象時給了我以下錯誤：

sqlalchemy.exc.InvalidRequestError: One or more mappers failed to initialize - can't proceed with initialization of other mappers. Triggering mapper: 'mapped class Specification->specifications'. Original exception was: Could not determine join condition between parent/child tables on relationship Specification.requirements - there are no foreign keys linking these tables.  Ensure that referencing columns are associated with a ForeignKey or ForeignKeyConstraint, or specify a 'primaryjoin' expression.

有誰知道如何實現這種關系？

Specification.requirements -> [Array of ItemSets]

任何指針都非常感謝。

Answer 1

您需要修改這兩個類：

class Specification(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(80), unique=True, nullable=False)
    comments = db.Column(db.String(255), nullable=True)
    
    # THIS IS THE BIT I AM UNSURE OF
    # Need this to a collection of Many ItemSets
    # Will the below work? 
    requirements = relationship("ItemSet", back_populates="spec")

class ItemSet(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    size = db.Column(db.Integer, db.ForeignKey('itemsizes.id'), nullable=True)
    count = db.Column(db.Integer, nullable=False)
    spec_id = Column(db.Integer, ForeignKey('spec.id'))
    spec = relationship("Specification", back_populates="requirements")