如何解决无法从具有一对多关系的模型中导入模式
我有两个具有一对多关系的模型:
from marshmallow import Schema,fields
from server import db,ma,app
from .category import CategorySchema
class Analysis(db.Model):
__tablename__ = 'Analysis'
__table_args__ = {'extend_existing': True}
id = db.Column(db.Integer,primary_key=True)
name = db.Column(db.String(120),index=True,unique=True)
description = db.Column(db.Text,nullable=False)
img = db.Column(db.LargeBinary,nullable=True)
img_mimetype = db.Column(db.Text,nullable=True)
img_name = db.Column(db.Text,nullable=True)
category_id = db.Column(db.Integer,db.ForeignKey('Categories.id'),nullable=True)
category = db.relationship("Category",back_populates="analysis")
class AnalysisSchema(ma.SQLAlchemyAutoSchema):
class Meta:
fields = ("id","name","description")
category = fields.Nested(CategorySchema(exclude=['img','analysis']))
from marshmallow import Schema,fields
from server import db,app
from sqlalchemy.ext.hybrid import hybrid_property
from .analysis import AnalysisSchema
class Category(db.Model):
__tablename__ = 'Categories'
__table_args__ = {'extend_existing': True}
id = db.Column(db.Integer,primary_key=True)
name = db.Column(db.String(120),unique=True)
description = db.Column(db.Text,nullable=False)
img = db.Column(db.LargeBinary,nullable=False)
img_mimetype = db.Column(db.Text,nullable=False)
img_name = db.Column(db.Text,nullable=False)
analysis = db.relationship("Analysis",back_populates="category")
@property
def img_url(self):
return "/categories/" + str(self.id)
class CategorySchema(ma.SQLAlchemyAutoSchema):
class Meta:
# model = Category
fields = ("id","description","img","img_url","analysis")
analysis = fields.Nested(AnalysisSchema,many=True)
class CreateCategorySchema(Schema):
name = fields.Str(required=True)
description = fields.Str(required=True)
class UpdateCategorySchema(Schema):
name = fields.Str(required=True)
description = fields.Str(required=False)
img = fields.Str(required=False)
img_name = fields.Str(required=False)
img_mimetype = fields.Str(required=False)
我不明白为什么会出现此错误:ImportError: cannot import name 'CategorySchema' from 'server.models.category' (/server/server/models/category.py)
Category 模型的导入效果很好,而 Analysis 模型中的导入没有。
解决方法
您可以通过将类名传递给 nested
as a string 来避免循环导入 - 这里的问题。例如:
class AnalysisSchema(ma.SQLAlchemyAutoSchema):
class Meta:
fields = ("id","name","description")
category = fields.Nested("CategorySchema",exclude=["img","analysis"])
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