Python SQLAlchemy: AttributeError: Neither 'Column' object nor 'Comparator' object has an attribute 'schema'
Question:
I tried creating a new database in my project, but I got this error when I run the script, I have another project using similar definition, it worked before, but now it get the same error now.
I am using Python 2.7.8 and the version of SQLAlchemy module is 0.9.8.
By the way, a project used Flask-SQLAlchemy, it works well.
I am confused.
The traceback information is following:
Traceback (most recent call last):
File "D:/Projects/OO-IM/db_create.py", line 4, in <module>
from models import Base
File "D:ProjectsOO-IMmodels.py", line 15, in <module>
Column('followed_id', Integer(), ForeignKey('user.id'))
File "C:Python27libsite-packagessqlalchemysqlschema.py", line 369, in __new__
schema = metadata.schema
File "C:Python27libsite-packagessqlalchemysqlelements.py", line 662, in __getattr__
key)
AttributeError: Neither 'Column' object nor 'Comparator' object has an attribute 'schema'
from sqlalchemy import (create_engine, Column,
String, Integer, Text,
DateTime, Boolean,
ForeignKey, Table)
from sqlalchemy.orm import sessionmaker, relationship, backref
from sqlalchemy.ext.declarative import declarative_base
SQLALCHEMY_DATABASE_URI = "mysql://root:mysqladmin@localhost:3306/oo_im?charset=utf8"
Base = declarative_base()
# TODO:AttributeError: Neither 'Column' object nor 'Comparator' object has an attribute 'schema'
friendships = Table('friendships',
Column('follower_id', Integer(), ForeignKey('user.id')),
Column('followed_id', Integer(), ForeignKey('user.id'))
)
class User(Base):
__tablename__ = 'user'
id = Column(Integer(), primary_key=True)
account = Column(String(32), unique=True, nullable=False)
password = Column(String(32), nullable=False)
followed = relationship("User",
secondary=friendships,
primaryjoin=(friendships.c.follower_id == id),
secondaryjoin=(friendships.c.followed_id == id),
backref=backref("followers", lazy="dynamic"),
lazy="dynamic")
def __init__(self, account, password, followed=None):
self.account = account
self.password = password
if followed:
for user in followed:
self.follow(user)
def follow(self, user):
if not self.is_following(user):
self.followed.append(user)
return self
def unfollow(self, user):
if self.is_following(user):
self.followed.remove(user)
return self
def is_following(self, user):
return self.followed.filter(friendships.c.followed_id == user.id).count() > 0
class ChatLog(Base):
__tablename__ = 'chatlog'
id = Column(Integer(), primary_key=True)
sender_id = Column(Integer(), ForeignKey('user.id'), nullable=False)
receiver_id = Column(Integer(), ForeignKey('user.id'), nullable=False)
send_time = Column(DateTime(), nullable=False)
received = Column(Boolean(), default=False)
content = Column(Text(), nullable=False)
engine = create_engine(SQLALCHEMY_DATABASE_URI, convert_unicode=True)
DBSession = sessionmaker(bind=engine)
Answers:
The table definition should be:
friendships = Table('friendships',
Base.metadata,
Column('follower_id', Integer(), ForeignKey('user.id')),
Column('followed_id', Integer(), ForeignKey('user.id'))
)
When defining tables using the declarative syntax, the metadata is inherited through the class declaration from Base, i.e.
Base = declarative_base()
class ChatLog(Base)
but, when defining tables using the old Table syntax, the metadata must be explicitly specified.
I had the same error because I spelled Column
with a lowercase c
. It should be Column
.
I faced the similar issue. Precisely, the error that I faced was :
AttributeError: Neither 'ColumnClause' object nor 'Comparator' object has an attribute '_set_parent_with_dispatch'
After a lot of struggle, I found out it was a spelling mistake. I spelled sa.Column as sa.column in below snippet line #6.
from alembic import op
import sqlalchemy as sa
def something():
op.add_column('table_name',
sa.Column('column_name', sa.Text(), nullable=True) # Correct usage
)
I tried creating a new database in my project, but I got this error when I run the script, I have another project using similar definition, it worked before, but now it get the same error now.
I am using Python 2.7.8 and the version of SQLAlchemy module is 0.9.8.
By the way, a project used Flask-SQLAlchemy, it works well.
I am confused.
The traceback information is following:
Traceback (most recent call last):
File "D:/Projects/OO-IM/db_create.py", line 4, in <module>
from models import Base
File "D:ProjectsOO-IMmodels.py", line 15, in <module>
Column('followed_id', Integer(), ForeignKey('user.id'))
File "C:Python27libsite-packagessqlalchemysqlschema.py", line 369, in __new__
schema = metadata.schema
File "C:Python27libsite-packagessqlalchemysqlelements.py", line 662, in __getattr__
key)
AttributeError: Neither 'Column' object nor 'Comparator' object has an attribute 'schema'
from sqlalchemy import (create_engine, Column,
String, Integer, Text,
DateTime, Boolean,
ForeignKey, Table)
from sqlalchemy.orm import sessionmaker, relationship, backref
from sqlalchemy.ext.declarative import declarative_base
SQLALCHEMY_DATABASE_URI = "mysql://root:mysqladmin@localhost:3306/oo_im?charset=utf8"
Base = declarative_base()
# TODO:AttributeError: Neither 'Column' object nor 'Comparator' object has an attribute 'schema'
friendships = Table('friendships',
Column('follower_id', Integer(), ForeignKey('user.id')),
Column('followed_id', Integer(), ForeignKey('user.id'))
)
class User(Base):
__tablename__ = 'user'
id = Column(Integer(), primary_key=True)
account = Column(String(32), unique=True, nullable=False)
password = Column(String(32), nullable=False)
followed = relationship("User",
secondary=friendships,
primaryjoin=(friendships.c.follower_id == id),
secondaryjoin=(friendships.c.followed_id == id),
backref=backref("followers", lazy="dynamic"),
lazy="dynamic")
def __init__(self, account, password, followed=None):
self.account = account
self.password = password
if followed:
for user in followed:
self.follow(user)
def follow(self, user):
if not self.is_following(user):
self.followed.append(user)
return self
def unfollow(self, user):
if self.is_following(user):
self.followed.remove(user)
return self
def is_following(self, user):
return self.followed.filter(friendships.c.followed_id == user.id).count() > 0
class ChatLog(Base):
__tablename__ = 'chatlog'
id = Column(Integer(), primary_key=True)
sender_id = Column(Integer(), ForeignKey('user.id'), nullable=False)
receiver_id = Column(Integer(), ForeignKey('user.id'), nullable=False)
send_time = Column(DateTime(), nullable=False)
received = Column(Boolean(), default=False)
content = Column(Text(), nullable=False)
engine = create_engine(SQLALCHEMY_DATABASE_URI, convert_unicode=True)
DBSession = sessionmaker(bind=engine)
The table definition should be:
friendships = Table('friendships',
Base.metadata,
Column('follower_id', Integer(), ForeignKey('user.id')),
Column('followed_id', Integer(), ForeignKey('user.id'))
)
When defining tables using the declarative syntax, the metadata is inherited through the class declaration from Base, i.e.
Base = declarative_base()
class ChatLog(Base)
but, when defining tables using the old Table syntax, the metadata must be explicitly specified.
I had the same error because I spelled Column
with a lowercase c
. It should be Column
.
I faced the similar issue. Precisely, the error that I faced was :
AttributeError: Neither 'ColumnClause' object nor 'Comparator' object has an attribute '_set_parent_with_dispatch'
After a lot of struggle, I found out it was a spelling mistake. I spelled sa.Column as sa.column in below snippet line #6.
from alembic import op
import sqlalchemy as sa
def something():
op.add_column('table_name',
sa.Column('column_name', sa.Text(), nullable=True) # Correct usage
)