sqlalchemy.exc.CircularDependencyError：检测到循环依赖

本文介绍了sqlalchemy.exc.CircularDependencyError：检测到循环依赖的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

业务逻辑-一个类别可能具有多个（1：M）属性，例如类别内存可能具有速度，大小，类型等属性。

The business logic - One Category may have multiple (1:M) attributes, like Category "Memory" could have attributes Speed, Size, Type etc.

at同时可以按属性值对一个Category进行排序（该属性存储在Category.sortByAttribute中-这是LookupCategoryAttributes表的外键。

at the same time one Category could be sorted by the attribute value (this is stored inside Category.sortByAttribute - which is foreign key to LookupCategoryAttributes table.

尝试通过SQLAlchemy构造它

Trying to construct it via SQLAlchemy, but getting circular dependency detected. What is wrong?

class Attribute(Base): __tablename__ = "LookupCategoryAttributes" types = ["date", "float", "integer", "select", "string", "text"] # Properties ID = Column(BigInteger, primary_key=True) categoryID = Column(BigInteger, ForeignKey('LookupCategories.ID'), nullable=False ) attribute = Column(VARCHAR(255), nullable=False) listValues = Column(VARCHAR(4000)) typeID = Column(VARCHAR(40), nullable=False) isRequired = Column(SmallInteger, nullable=False, default=0) displayInMenu = Column(SmallInteger, nullable=False, default=0) displayInFilter = Column(SmallInteger, nullable=False, default=0) class Category(Base): __tablename__ = "LookupCategories" # Properties ID = Column(BigInteger, primary_key=True) category = Column(VARCHAR(255), nullable=False) description = Column(VARCHAR(1000), nullable=False) parentCategoryID = Column(BigInteger, ForeignKey('LookupCategories.ID')) leftPos = Column(Integer) rightPos = Column(Integer) sortByAttribute = Column(BigInteger, ForeignKey('LookupCategoryAttributes.ID')) sortOrder = Column(SmallInteger, default=1) # Relationships ParentCategory = relationship("Category", uselist=False, remote_side=[ID], backref='SubCategories') SortByAttribute = relationship("Attribute", uselist=False, foreign_keys=[sortByAttribute], primaryjoin="Attribute.ID==Category.sortByAttribute") Attributes = relationship("Attribute", backref="Category", primaryjoin="Attribute.categoryID==Category.ID")

，然后代码如下所示：

category = Category(record['Name'], extID=extID) attr1 = Attribute(v) attr2 = Attribute(v) category.Attributes.append(attr1) category.Attributes.append(attr2) category.SortByAttribute = attr1

当我执行提交时，我得到：

when I execute commit I get:

sqlalchemy.exc.CircularDependencyError: Circular dependency detected.

推荐答案

确定了答案-在关系$ b中使用post_update $ b docs.sqlalchemy/en/latest /orm/relationship_persistence.html#post-update

Okay found the answer - use post_update in relationship docs.sqlalchemy/en/latest/orm/relationship_persistence.html#post-update

所以我在 Category 类中所做的更改如下：

so what I did is inside Category class is changed this:

SortByAttribute = relationship( "Attribute", uselist=False, foreign_keys=[sortByAttribute], primaryjoin="Attribute.ID==Category.sortByAttribute" )

为此：

SortByAttribute = relationship( "Attribute", uselist=False, foreign_keys=[sortByAttribute], primaryjoin="Attribute.ID==Category.sortByAttribute", post_update=True )