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@elemoine
Created August 5, 2019 15:16
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from sqlalchemy import Column, Integer, String, ForeignKey, MetaData, create_engine
from sqlalchemy.orm import sessionmaker, relationship, scoped_session
from sqlalchemy.ext.declarative import declarative_base
from marshmallow import fields
from marshmallow_sqlalchemy import ModelSchema
engine = create_engine("postgresql://elemoine@localhost/gis", echo=True)
metadata = MetaData(engine)
Base = declarative_base(metadata=metadata)
Session = scoped_session(sessionmaker(bind=engine))
#
# Define SQLAlchemy models
#
class Parent(Base):
__tablename__ = "parent"
id = Column(Integer, ForeignKey("child.id", ondelete="CASCADE"), primary_key=True)
child = relationship("Child", lazy="joined")
class Child(Base):
__tablename__ = "child"
id = Column(Integer, primary_key=True)
name = Column(String)
#
# Define Marshmallow model schemas
#
class ParentSchema(ModelSchema):
class Meta:
model = Parent
sqla_session = Session
child = fields.Nested("ChildSchema")
class ChildSchema(ModelSchema):
class Meta:
model = Child
sqla_session = Session
#
# Create the tables in the database
#
metadata.drop_all(checkfirst=True)
metadata.create_all()
#
# Add objects to the database
#
parent = Parent()
child = Child()
child.id = 1
child.name = "name"
parent.child = child
Session.add(parent)
Session.commit()
#
# Load objects using marshmallow-sqalchemy and trigger the "FlushError: New instance <>
# with identity key () conflicts with persistent instance <>" error
#
Session.expunge_all()
parent = Session.query(Parent).one()
json_data = {"child": {"id": 1, "name": "new name"}}
with Session.no_autoflush:
instance = ParentSchema().load(json_data)
Session.add(instance.data)
Session.commit()
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