【发布时间】：2020-10-02 21:27:16
【问题描述】：
在声明我的两个模型之间的关系时（存储在两个单独的文件中，我收到以下错误：
ERROR: sqlalchemy.exc.InvalidRequestError: When initializing mapper mapped class FrequencyBand->frequency_bands_table, expression 'LicenseItem' failed to locate a name ('LicenseItem'). If this is a class name, consider adding this relationship() to the <class 'src.models.metaData.FrequencyBand'> class after both dependent classes have been defined.
我认为通过使用字符串表示（通过声明性基础）可以避免这个问题 -> 但似乎我在设置映射器之前导入了 FrequencyBand-Object。我该如何解决？ （作为一种解决方法，我在 LicenseItem 上声明了关系，但我对其他关系也有类似的问题）。任何想法/提示？非常感谢任何帮助！
class FrequencyBand(db.Model):
__tablename__ = "frequency_bands_table"
band_id = db.Column(db.String(20), primary_key=True)
band_nr = db.Column(db.Integer)
name = db.Column(db.String(50))
technology = db.Column(db.String(20))
license = db.relationship("LicenseItem")
license_id = db.Column(db.String(100), db.ForeignKey('license_items_table.item_id'))
class Item(db.Model):
__tablename__ = 'items_table'
item_id = db.Column(db.String(20), primary_key=True)
category = db.Column(db.Enum("Antennen", "Radio", "Diverses", "Lizenzen"))
name = db.Column(db.String(100))
description = db.Column(db.String(100))
otc = db.Column(db.Integer)
mrc = db.Column(db.Integer)
custom_price = db.Column(db.Boolean)
item_status = db.Column(db.Enum("active", "inactive"))
last_updated_at = db.Column(db.DateTime(timezone=True), onupdate=func.now())
__mapper_args__ = {
'polymorphic_identity':'Item',
'polymorphic_on':category
}
def __str__(self):
return self.name
class MiscellaneousItem(Item):
__mapper_args__ = { 'polymorphic_identity':'Diverses'}
__tablename__ = 'miscellaneous_items_table'
item_id = db.Column(db.String(20), db.ForeignKey('items_table.item_id'), primary_key=True)
class MiscellaneousItemSchema(marshmallow.SQLAlchemyAutoSchema):
class Meta:
model = MiscellaneousItem
include_fk = True
class AntennaItem(Item):
__mapper_args__ = { 'polymorphic_identity':'Antennen'}
__tablename__ = 'antenna_items_table'
item_id = db.Column(db.String(20), db.ForeignKey('items_table.item_id'), primary_key=True)
hardware_types = db.relationship("HardwareType", secondary=item_hw_type_table)
frequency_bands = db.relationship("FrequencyBand", secondary=item_frequency_table)
mimo_layers = db.Column(db.Integer)
nrOfBands = db.Column(db.Integer)
allowed_SLA_types = db.relationship("SLAType", secondary=item_sla_types_table)
class LicenseItem(Item): #Item-Subclass --> Joined table inheritance
__mapper_args__ = { 'polymorphic_identity':'Lizenzen'}
__tablename__ = 'license_items_table'
item_id = db.Column(db.String(20), db.ForeignKey('items_table.item_id'), primary_key=True)
frequencies = db.relationship("FrequencyBand", backref="license")
由于我为我的烧瓶应用程序使用命名空间和蓝图，因此模型在命名空间中导入，并且蓝图通过应用程序工厂模式注册。
from flask import Blueprint
from flask_restx import Api
from .meta_data import ns as meta_data_ns
from .projects import ns as projects_ns
api_blueprint = Blueprint('api', __name__)
api = Api(api_blueprint)
api.add_namespace(meta_data_ns, path='/meta')
api.add_namespace(projects_ns, path='/projects')
#meta namespace -> the first namespace which is registered -> and therefore the FrequencyBand is imported before LicenseItem is declared
from flask_restx import Namespace, Resource
from src.models.metaData import FrequencyBand
from src.models.item import Item, AllItemsSchema
from src.models.utils import token_required
ns = Namespace('meta', description='Operations related to meta data')
@ns.route('/')
class UnitObject(Resource):
@token_required
def get(self):
#...
#app.__init__
from flask import Flask
from .extensions import db,...
from src.config import app_config
def create_app(config_name):
"""Create and return app."""
app = Flask(__name__)
app.config.from_object(app_config[config_name])
db.init_app(app)
marshmallow.init_app(app)
...
with app.app_context():
from src.api import api_blueprint
from src.admin_backend.commands import bp as command_bp
app.register_blueprint(api_blueprint, url_prefix="/api")
app.register_blueprint(command_bp)
return app
【问题讨论】：
-
你能发布项目类吗？如果没有 Item 类，您的代码对我有用。
-
感谢您的支持。我添加了 Item 类。我还意识到 db 引用的是 flask_sqlalchemy （而不是 sqlalchemy，但我知道这两个应该是相同的）。但是可能是 Joined table 继承导致了一些问题？
标签： python flask orm sqlalchemy flask-sqlalchemy