我有以下代码尝试使用关联对象创建父子多对多关系。 ParentChild（关联表）要有一个包含parent_id，child_id和unc
的组合键timestamp.
import os
import sys
import psycopg2
from datetime import datetime
from sqlalchemy import Column, ForeignKey, Integer, String, Date
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import relationship, Session
from sqlalchemy import create_engine
Base = declarative_base()
class ParentChild(Base):
__tablename__ = 'parentchild'
parent_id = Column(Integer, ForeignKey('parent.id'), primary_key=True)
child_id = Column(Integer, ForeignKey('child.id'), primary_key=True)
timestamp = Column(Date, primary_key=True)
child = relationship("Child", back_populates="parents")
parent = relationship("Parent", back_populates="children")
class Parent(Base):
__tablename__ = 'parent'
id = Column(Integer, autoincrement=True, primary_key=True)
name = Column(String)
age = Column(Integer)
children = relationship('ParentChild', back_populates="parent")
class Child(Base):
__tablename__ = 'child'
id = Column(Integer, autoincrement=True, primary_key=True)
name = Column(String)
age = Column(Integer)
parents = relationship('ParentChild', back_populates='child')
engine = create_engine('blah blah blah')
Base.metadata.create_all(engine)
session = Session(engine)
parent1 = Parent(name='Mark', age='28')
session.add(parent1)
child1 = Child(name='Jack', age='3')
session.add(child1)
family1 = ParentChild(timestamp = datetime.utcnow())
family1.child = child1.id
parent1.children.append(family1)
session.add(family1)
session.commit()
这会导致错误消息；
SAWarning: Column 'parentchild.child_id' is marked as a member of the primary key for table 'parentchild', but has no Python-side or server-side default generator indicated, nor does it indicate 'autoincrement=True' or 'nullable=True', and no explicit value is passed. Primary key columns typically may not store NULL. Note that as of SQLAlchemy 1.1, 'autoincrement=True' must be indicated explicitly for composite (e.g. multicolumn) primary keys if AUTO_INCREMENT/SERIAL/IDENTITY behavior is expected for one of the columns in the primary key. CREATE TABLE statements are impacted by this change as well on most backends.
util.warn(msg)
Traceback (most recent call last):
File "C:\Users\markp\AppData\Local\Programs\Python\Python37\lib\site-packages\sqlalchemy\engine\base.py", line 1193, in _execute_context
context)
File "C:\Users\markp\AppData\Local\Programs\Python\Python37\lib\site-packages\sqlalchemy\engine\default.py", line 509, in do_execute
cursor.execute(statement, parameters)
psycopg2.IntegrityError: null value in column "child_id" violates not-null constraint
DETAIL: Failing row contains (2, null, 2018-11-18).
The above exception was the direct cause of the following exception:
Traceback (most recent call last):
File "c:/Users/markp/OneDrive/Code/agile_metrics/test_assoc.py", line 50, in <module>
session.commit()
File "C:\Users\markp\AppData\Local\Programs\Python\Python37\lib\site-packages\sqlalchemy\orm\session.py", line 954, in commit
self.transaction.commit()
File "C:\Users\markp\AppData\Local\Programs\Python\Python37\lib\site-packages\sqlalchemy\orm\session.py", line 467, in commit
self._prepare_impl()
File "C:\Users\markp\AppData\Local\Programs\Python\Python37\lib\site-packages\sqlalchemy\orm\session.py", line 447, in _prepare_impl
self.session.flush()
File "C:\Users\markp\AppData\Local\Programs\Python\Python37\lib\site-packages\sqlalchemy\orm\session.py", line 2313, in flush
self._flush(objects)
File "C:\Users\markp\AppData\Local\Programs\Python\Python37\lib\site-packages\sqlalchemy\orm\session.py", line 2440, in _flush
transaction.rollback(_capture_exception=True)
File "C:\Users\markp\AppData\Local\Programs\Python\Python37\lib\site-packages\sqlalchemy\util\langhelpers.py", line 66, in __exit__
compat.reraise(exc_type, exc_value, exc_tb)
File "C:\Users\markp\AppData\Local\Programs\Python\Python37\lib\site-packages\sqlalchemy\util\compat.py", line 249, in reraise
raise value
File "C:\Users\markp\AppData\Local\Programs\Python\Python37\lib\site-packages\sqlalchemy\orm\session.py", line 2404, in _flush
flush_context.execute()
File "C:\Users\markp\AppData\Local\Programs\Python\Python37\lib\site-packages\sqlalchemy\orm\unitofwork.py", line 395, in execute
rec.execute(self)
File "C:\Users\markp\AppData\Local\Programs\Python\Python37\lib\site-packages\sqlalchemy\orm\unitofwork.py", line 560, in execute
uow
File "C:\Users\markp\AppData\Local\Programs\Python\Python37\lib\site-packages\sqlalchemy\orm\persistence.py", line 181, in save_obj
mapper, table, insert)
File "C:\Users\markp\AppData\Local\Programs\Python\Python37\lib\site-packages\sqlalchemy\orm\persistence.py", line 872, in _emit_insert_statements
execute(statement, params)
File "C:\Users\markp\AppData\Local\Programs\Python\Python37\lib\site-packages\sqlalchemy\engine\base.py", line 948, in execute
return meth(self, multiparams, params)
File "C:\Users\markp\AppData\Local\Programs\Python\Python37\lib\site-packages\sqlalchemy\sql\elements.py", line 269, in _execute_on_connection
return connection._execute_clauseelement(self, multiparams, params)
File "C:\Users\markp\AppData\Local\Programs\Python\Python37\lib\site-packages\sqlalchemy\engine\base.py", line 1060, in _execute_clauseelement
compiled_sql, distilled_params
File "C:\Users\markp\AppData\Local\Programs\Python\Python37\lib\site-packages\sqlalchemy\engine\base.py", line 1200, in _execute_context
context)
File "C:\Users\markp\AppData\Local\Programs\Python\Python37\lib\site-packages\sqlalchemy\engine\base.py", line 1413, in _handle_dbapi_exception
exc_info
File "C:\Users\markp\AppData\Local\Programs\Python\Python37\lib\site-packages\sqlalchemy\util\compat.py", line 265, in raise_from_cause
reraise(type(exception), exception, tb=exc_tb, cause=cause)
File "C:\Users\markp\AppData\Local\Programs\Python\Python37\lib\site-packages\sqlalchemy\util\compat.py", line 248, in reraise
raise value.with_traceback(tb)
File "C:\Users\markp\AppData\Local\Programs\Python\Python37\lib\site-packages\sqlalchemy\engine\base.py", line 1193, in _execute_context
context)
File "C:\Users\markp\AppData\Local\Programs\Python\Python37\lib\site-packages\sqlalchemy\engine\default.py", line 509, in do_execute
cursor.execute(statement, parameters)
sqlalchemy.exc.IntegrityError: (psycopg2.IntegrityError) null value in column "child_id" violates not-null constraint
DETAIL: Failing row contains (2, null, 2018-11-18).
[SQL: 'INSERT INTO parentchild (parent_id, timestamp) VALUES (%(parent_id)s, %(timestamp)s)'] [parameters: {'parent_id': 2, 'timestamp': datetime.datetime(2018, 11, 18, 11, 25, 34, 667000)}] (Background on this error at: http://sqlalche.me/e/gkpj)
关于如何解决此问题的任何想法？
谢谢 标记