[sqlalchemy] Re: Self-Referential Mapping with Base?
Must have been a bug in the default constructor prior to 0.5.0 final.
I got the same error rerunning with earlier version. Strange, I don't
remember now how I had this running before. Maybe with my own
constructor, but not worth igging to find out, it works with final
release.
On Jan 11, 1:43 pm, Darren Govoni dar...@ontrenet.com wrote:
Ahhh, looks like I'm on rc4. Let me try final and see.
On Sun, 2009-01-11 at 13:10 -0500, Michael Bayer wrote:
0.5.0 final ?
On Jan 11, 2009, at 12:21 PM, Darren Govoni wrote:
Hi MikeCo,
I tried your example, and got this error from SA 0.5.
ValueError: need more than 0 values to unpack
Darren
On Fri, 2009-01-09 at 20:33 -0800, MikeCo wrote:
from sqlalchemy import *
from sqlalchemy.orm import *
from sqlalchemy.ext.declarative import declarative_base
dbname = ''
dburl = 'sqlite:///%s' % dbname
# set up environment
eng = create_engine(dburl, echo=False)
meta = MetaData(bind=eng)
Base = declarative_base(metadata=meta)
Session = sessionmaker()
# D self referential
class D(Base):
__tablename__ = 'D'
id = Column(Integer, primary_key=True)
id_d = Column(Integer, ForeignKey('D.id'))
name = Column(Text)
child = relation('D',
backref=backref('parent', remote_side='D.id'))
def __repr__(self):
return '--D (id:%s-id_d:%s) %s --' % (self.id, self.id_d,
self.name)
def initdb():
print '# create the database'
meta.drop_all(checkfirst=True)
meta.create_all()
sess = Session()
# insert some data for self-reference relationship
for ddata in ('d-one', 'd-two'):
dobj = D(name=ddata)
sess.add(dobj)
dobj2 = D(name=ddata+'-child1')
dobj.child.append(dobj2)
dobj2 = D(name=ddata+'-child2')
dobj.child.append(dobj2)
dobj3 = D(name=ddata+'-child2'+'-child3')
dobj2.child.append(dobj3)
sess.commit()
sess.close()
def printobj(obj, indent=''):
# recursive list
print '%s%s' % (indent, obj)
if hasattr(obj, 'child'):
for ch in obj.child:
printobj(ch, indent=indent+' ')
def listd():
# retrieve and list
sess = Session()
print '# D-D'
query = sess.query(D).filter(D.id_d==None).order_by(D.name)
for dobj in query:
printobj(dobj)
sess.close()
def tst3():
# do stuff with self referential class D
sess = Session()
print #switch parentage of name 'd-two-child1' to 'd-one'
print '# before'
listd()
child = sess.query(D).filter(D.name=='d-two-child1').one()
parent = sess.query(D).filter(D.name=='d-one').one()
eng.echo=True
child.parent = parent
child.name += ' MOVED'
sess.commit()
eng.echo=False
print '# after'
listd()
initdb()
tst3()
--~--~-~--~~~---~--~~
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[sqlalchemy] Re: Self-Referential Mapping with Base?
yes, it was a bug that declarative wasn't translating the backref()
arguments from strings.
On Jan 12, 2009, at 10:22 AM, MikeCo wrote:
Must have been a bug in the default constructor prior to 0.5.0 final.
I got the same error rerunning with earlier version. Strange, I don't
remember now how I had this running before. Maybe with my own
constructor, but not worth igging to find out, it works with final
release.
On Jan 11, 1:43 pm, Darren Govoni dar...@ontrenet.com wrote:
Ahhh, looks like I'm on rc4. Let me try final and see.
On Sun, 2009-01-11 at 13:10 -0500, Michael Bayer wrote:
0.5.0 final ?
On Jan 11, 2009, at 12:21 PM, Darren Govoni wrote:
Hi MikeCo,
I tried your example, and got this error from SA 0.5.
ValueError: need more than 0 values to unpack
Darren
On Fri, 2009-01-09 at 20:33 -0800, MikeCo wrote:
from sqlalchemy import *
from sqlalchemy.orm import *
from sqlalchemy.ext.declarative import declarative_base
dbname = ''
dburl = 'sqlite:///%s' % dbname
# set up environment
eng = create_engine(dburl, echo=False)
meta = MetaData(bind=eng)
Base = declarative_base(metadata=meta)
Session = sessionmaker()
# D self referential
class D(Base):
__tablename__ = 'D'
id = Column(Integer, primary_key=True)
id_d = Column(Integer, ForeignKey('D.id'))
name = Column(Text)
child = relation('D',
backref=backref('parent', remote_side='D.id'))
def __repr__(self):
return '--D (id:%s-id_d:%s) %s --' % (self.id,
self.id_d,
self.name)
def initdb():
print '# create the database'
meta.drop_all(checkfirst=True)
meta.create_all()
sess = Session()
# insert some data for self-reference relationship
for ddata in ('d-one', 'd-two'):
dobj = D(name=ddata)
sess.add(dobj)
dobj2 = D(name=ddata+'-child1')
dobj.child.append(dobj2)
dobj2 = D(name=ddata+'-child2')
dobj.child.append(dobj2)
dobj3 = D(name=ddata+'-child2'+'-child3')
dobj2.child.append(dobj3)
sess.commit()
sess.close()
def printobj(obj, indent=''):
# recursive list
print '%s%s' % (indent, obj)
if hasattr(obj, 'child'):
for ch in obj.child:
printobj(ch, indent=indent+'')
def listd():
# retrieve and list
sess = Session()
print '# D-D'
query = sess.query(D).filter(D.id_d==None).order_by(D.name)
for dobj in query:
printobj(dobj)
sess.close()
def tst3():
# do stuff with self referential class D
sess = Session()
print #switch parentage of name 'd-two-child1' to 'd-one'
print '# before'
listd()
child = sess.query(D).filter(D.name=='d-two-child1').one()
parent = sess.query(D).filter(D.name=='d-one').one()
eng.echo=True
child.parent = parent
child.name += ' MOVED'
sess.commit()
eng.echo=False
print '# after'
listd()
initdb()
tst3()
--~--~-~--~~~---~--~~
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sqlalchemy group.
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-~--~~~~--~~--~--~---
[sqlalchemy] Re: Self-Referential Mapping with Base?
Hi MikeCo,
I tried your example, and got this error from SA 0.5.
ValueError: need more than 0 values to unpack
Darren
On Fri, 2009-01-09 at 20:33 -0800, MikeCo wrote:
from sqlalchemy import *
from sqlalchemy.orm import *
from sqlalchemy.ext.declarative import declarative_base
dbname = ''
dburl = 'sqlite:///%s' % dbname
# set up environment
eng = create_engine(dburl, echo=False)
meta = MetaData(bind=eng)
Base = declarative_base(metadata=meta)
Session = sessionmaker()
# D self referential
class D(Base):
__tablename__ = 'D'
id = Column(Integer, primary_key=True)
id_d = Column(Integer, ForeignKey('D.id'))
name = Column(Text)
child = relation('D',
backref=backref('parent', remote_side='D.id'))
def __repr__(self):
return '--D (id:%s-id_d:%s) %s --' % (self.id, self.id_d,
self.name)
def initdb():
print '# create the database'
meta.drop_all(checkfirst=True)
meta.create_all()
sess = Session()
# insert some data for self-reference relationship
for ddata in ('d-one', 'd-two'):
dobj = D(name=ddata)
sess.add(dobj)
dobj2 = D(name=ddata+'-child1')
dobj.child.append(dobj2)
dobj2 = D(name=ddata+'-child2')
dobj.child.append(dobj2)
dobj3 = D(name=ddata+'-child2'+'-child3')
dobj2.child.append(dobj3)
sess.commit()
sess.close()
def printobj(obj, indent=''):
# recursive list
print '%s%s' % (indent, obj)
if hasattr(obj, 'child'):
for ch in obj.child:
printobj(ch, indent=indent+'')
def listd():
# retrieve and list
sess = Session()
print '# D-D'
query = sess.query(D).filter(D.id_d==None).order_by(D.name)
for dobj in query:
printobj(dobj)
sess.close()
def tst3():
# do stuff with self referential class D
sess = Session()
print #switch parentage of name 'd-two-child1' to 'd-one'
print '# before'
listd()
child = sess.query(D).filter(D.name=='d-two-child1').one()
parent = sess.query(D).filter(D.name=='d-one').one()
eng.echo=True
child.parent = parent
child.name += ' MOVED'
sess.commit()
eng.echo=False
print '# after'
listd()
initdb()
tst3()
--~--~-~--~~~---~--~~
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-~--~~~~--~~--~--~---
[sqlalchemy] Re: Self-Referential Mapping with Base?
0.5.0 final ?
On Jan 11, 2009, at 12:21 PM, Darren Govoni wrote:
Hi MikeCo,
I tried your example, and got this error from SA 0.5.
ValueError: need more than 0 values to unpack
Darren
On Fri, 2009-01-09 at 20:33 -0800, MikeCo wrote:
from sqlalchemy import *
from sqlalchemy.orm import *
from sqlalchemy.ext.declarative import declarative_base
dbname = ''
dburl = 'sqlite:///%s' % dbname
# set up environment
eng = create_engine(dburl, echo=False)
meta = MetaData(bind=eng)
Base = declarative_base(metadata=meta)
Session = sessionmaker()
# D self referential
class D(Base):
__tablename__ = 'D'
id = Column(Integer, primary_key=True)
id_d = Column(Integer, ForeignKey('D.id'))
name = Column(Text)
child = relation('D',
backref=backref('parent', remote_side='D.id'))
def __repr__(self):
return '--D (id:%s-id_d:%s) %s --' % (self.id, self.id_d,
self.name)
def initdb():
print '# create the database'
meta.drop_all(checkfirst=True)
meta.create_all()
sess = Session()
# insert some data for self-reference relationship
for ddata in ('d-one', 'd-two'):
dobj = D(name=ddata)
sess.add(dobj)
dobj2 = D(name=ddata+'-child1')
dobj.child.append(dobj2)
dobj2 = D(name=ddata+'-child2')
dobj.child.append(dobj2)
dobj3 = D(name=ddata+'-child2'+'-child3')
dobj2.child.append(dobj3)
sess.commit()
sess.close()
def printobj(obj, indent=''):
# recursive list
print '%s%s' % (indent, obj)
if hasattr(obj, 'child'):
for ch in obj.child:
printobj(ch, indent=indent+'')
def listd():
# retrieve and list
sess = Session()
print '# D-D'
query = sess.query(D).filter(D.id_d==None).order_by(D.name)
for dobj in query:
printobj(dobj)
sess.close()
def tst3():
# do stuff with self referential class D
sess = Session()
print #switch parentage of name 'd-two-child1' to 'd-one'
print '# before'
listd()
child = sess.query(D).filter(D.name=='d-two-child1').one()
parent = sess.query(D).filter(D.name=='d-one').one()
eng.echo=True
child.parent = parent
child.name += ' MOVED'
sess.commit()
eng.echo=False
print '# after'
listd()
initdb()
tst3()
--~--~-~--~~~---~--~~
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-~--~~~~--~~--~--~---
[sqlalchemy] Re: Self-Referential Mapping with Base?
Ahhh, looks like I'm on rc4. Let me try final and see.
On Sun, 2009-01-11 at 13:10 -0500, Michael Bayer wrote:
0.5.0 final ?
On Jan 11, 2009, at 12:21 PM, Darren Govoni wrote:
Hi MikeCo,
I tried your example, and got this error from SA 0.5.
ValueError: need more than 0 values to unpack
Darren
On Fri, 2009-01-09 at 20:33 -0800, MikeCo wrote:
from sqlalchemy import *
from sqlalchemy.orm import *
from sqlalchemy.ext.declarative import declarative_base
dbname = ''
dburl = 'sqlite:///%s' % dbname
# set up environment
eng = create_engine(dburl, echo=False)
meta = MetaData(bind=eng)
Base = declarative_base(metadata=meta)
Session = sessionmaker()
# D self referential
class D(Base):
__tablename__ = 'D'
id = Column(Integer, primary_key=True)
id_d = Column(Integer, ForeignKey('D.id'))
name = Column(Text)
child = relation('D',
backref=backref('parent', remote_side='D.id'))
def __repr__(self):
return '--D (id:%s-id_d:%s) %s --' % (self.id, self.id_d,
self.name)
def initdb():
print '# create the database'
meta.drop_all(checkfirst=True)
meta.create_all()
sess = Session()
# insert some data for self-reference relationship
for ddata in ('d-one', 'd-two'):
dobj = D(name=ddata)
sess.add(dobj)
dobj2 = D(name=ddata+'-child1')
dobj.child.append(dobj2)
dobj2 = D(name=ddata+'-child2')
dobj.child.append(dobj2)
dobj3 = D(name=ddata+'-child2'+'-child3')
dobj2.child.append(dobj3)
sess.commit()
sess.close()
def printobj(obj, indent=''):
# recursive list
print '%s%s' % (indent, obj)
if hasattr(obj, 'child'):
for ch in obj.child:
printobj(ch, indent=indent+'')
def listd():
# retrieve and list
sess = Session()
print '# D-D'
query = sess.query(D).filter(D.id_d==None).order_by(D.name)
for dobj in query:
printobj(dobj)
sess.close()
def tst3():
# do stuff with self referential class D
sess = Session()
print #switch parentage of name 'd-two-child1' to 'd-one'
print '# before'
listd()
child = sess.query(D).filter(D.name=='d-two-child1').one()
parent = sess.query(D).filter(D.name=='d-one').one()
eng.echo=True
child.parent = parent
child.name += ' MOVED'
sess.commit()
eng.echo=False
print '# after'
listd()
initdb()
tst3()
--~--~-~--~~~---~--~~
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sqlalchemy group.
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-~--~~~~--~~--~--~---
[sqlalchemy] Re: Self-Referential Mapping with Base?
One thing to notice about ignoring the ids completely. This can
introduce inefficiencies when updating records. In the sample function
tst3() the line
child.parent = parent
causes SA to read the old parent record to get the attribute
child.parent. Changing to:
child.id_d = parent.id
eliminates the extra SELECT statement.
Inefficiencies like that are pretty rare.
On Jan 9, 11:33 pm, MikeCo mconl...@gmail.com wrote:
I spent some time understanding this a little while ago. Here is the
construct you need
(thanks to Michael Bayer for making it clear for me)
# D self referential
class D(Base):
__tablename__ = 'D'
id = Column(Integer, primary_key=True)
id_d = Column(Integer, ForeignKey('D.id'))
name = Column(Text)
child = relation('D', backref=backref('parent',
remote_side='D.id'))
The 'child' relation establishes the two way linkage you want.
One of the key things to think about is to use objects as normal
python data structures. Generally you don't need to manipulate ids;
let SQLAlchemy worry about that.
Here is sample script I used when learning the topic
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
from sqlalchemy import *
from sqlalchemy.orm import *
from sqlalchemy.ext.declarative import declarative_base
dbname = ''
dburl = 'sqlite:///%s' % dbname
# set up environment
eng = create_engine(dburl, echo=False)
meta = MetaData(bind=eng)
Base = declarative_base(metadata=meta)
Session = sessionmaker()
# D self referential
class D(Base):
__tablename__ = 'D'
id = Column(Integer, primary_key=True)
id_d = Column(Integer, ForeignKey('D.id'))
name = Column(Text)
child = relation('D',
backref=backref('parent', remote_side='D.id'))
def __repr__(self):
return '--D (id:%s-id_d:%s) %s --' % (self.id, self.id_d,
self.name)
def initdb():
print '# create the database'
meta.drop_all(checkfirst=True)
meta.create_all()
sess = Session()
# insert some data for self-reference relationship
for ddata in ('d-one', 'd-two'):
dobj = D(name=ddata)
sess.add(dobj)
dobj2 = D(name=ddata+'-child1')
dobj.child.append(dobj2)
dobj2 = D(name=ddata+'-child2')
dobj.child.append(dobj2)
dobj3 = D(name=ddata+'-child2'+'-child3')
dobj2.child.append(dobj3)
sess.commit()
sess.close()
def printobj(obj, indent=''):
# recursive list
print '%s%s' % (indent, obj)
if hasattr(obj, 'child'):
for ch in obj.child:
printobj(ch, indent=indent+' ')
def listd():
# retrieve and list
sess = Session()
print '# D-D'
query = sess.query(D).filter(D.id_d==None).order_by(D.name)
for dobj in query:
printobj(dobj)
sess.close()
def tst3():
# do stuff with self referential class D
sess = Session()
print #switch parentage of name 'd-two-child1' to 'd-one'
print '# before'
listd()
child = sess.query(D).filter(D.name=='d-two-child1').one()
parent = sess.query(D).filter(D.name=='d-one').one()
eng.echo=True
child.parent = parent
child.name += ' MOVED'
sess.commit()
eng.echo=False
print '# after'
listd()
initdb()
tst3()
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
On Jan 9, 10:03 pm, Darren Govoni dar...@ontrenet.com wrote:
Hi,
Thanks for the response. I'm still fairly new to SA but am very
impressed with this package!
I tried a variety of combinations of mappings. If I use just the
parent_id,parent it would seem to make sense logically if my children
only have one parent.
The tables generate fine. But when I try to set the parent of a child at
runtime it throws an exception about Conversion not being a list or
collection or something. So I was experimenting with the M2M, and as you
see, its not right.
Logically, the self referring parent should be enough I would think. Is
there another way using Base without having to use another mapping
technique since all my other classes are Base derived?
Thank you.
On Fri, 2009-01-09 at 20:17 -0500, Michael Bayer wrote:
On Jan 9, 2009, at 7:42 PM, project2501 wrote:
Hi,
I'm trying to create a mapped class that allows parent/child
relation of itself. I've spent the last 3 hours searching and reading
the other posts on this, but can't get anything to work.
I'm on 0.5rc4 and just want to declare this in a mapped class as such:
class Conversion(Base):
__tablename__ = 'conversion'
id = Column(Integer, primary_key=True)
name = Column(String(20))
parent_id = Column(Integer, ForeignKey('conversion.id'))
parent = relation(Conversion, backref=child)
children = relation('Conversion', secondary=conversion_conversion,
backref='parents')
I was hoping to use the same style many-to-many declarations
[sqlalchemy] Re: Self-Referential Mapping with Base?
Interesting to know.
Appreciate the examples!
On Sat, 2009-01-10 at 05:38 -0800, MikeCo wrote:
One thing to notice about ignoring the ids completely. This can
introduce inefficiencies when updating records. In the sample function
tst3() the line
child.parent = parent
causes SA to read the old parent record to get the attribute
child.parent. Changing to:
child.id_d = parent.id
eliminates the extra SELECT statement.
Inefficiencies like that are pretty rare.
On Jan 9, 11:33 pm, MikeCo mconl...@gmail.com wrote:
I spent some time understanding this a little while ago. Here is the
construct you need
(thanks to Michael Bayer for making it clear for me)
# D self referential
class D(Base):
__tablename__ = 'D'
id = Column(Integer, primary_key=True)
id_d = Column(Integer, ForeignKey('D.id'))
name = Column(Text)
child = relation('D', backref=backref('parent',
remote_side='D.id'))
The 'child' relation establishes the two way linkage you want.
One of the key things to think about is to use objects as normal
python data structures. Generally you don't need to manipulate ids;
let SQLAlchemy worry about that.
Here is sample script I used when learning the topic
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
from sqlalchemy import *
from sqlalchemy.orm import *
from sqlalchemy.ext.declarative import declarative_base
dbname = ''
dburl = 'sqlite:///%s' % dbname
# set up environment
eng = create_engine(dburl, echo=False)
meta = MetaData(bind=eng)
Base = declarative_base(metadata=meta)
Session = sessionmaker()
# D self referential
class D(Base):
__tablename__ = 'D'
id = Column(Integer, primary_key=True)
id_d = Column(Integer, ForeignKey('D.id'))
name = Column(Text)
child = relation('D',
backref=backref('parent', remote_side='D.id'))
def __repr__(self):
return '--D (id:%s-id_d:%s) %s --' % (self.id, self.id_d,
self.name)
def initdb():
print '# create the database'
meta.drop_all(checkfirst=True)
meta.create_all()
sess = Session()
# insert some data for self-reference relationship
for ddata in ('d-one', 'd-two'):
dobj = D(name=ddata)
sess.add(dobj)
dobj2 = D(name=ddata+'-child1')
dobj.child.append(dobj2)
dobj2 = D(name=ddata+'-child2')
dobj.child.append(dobj2)
dobj3 = D(name=ddata+'-child2'+'-child3')
dobj2.child.append(dobj3)
sess.commit()
sess.close()
def printobj(obj, indent=''):
# recursive list
print '%s%s' % (indent, obj)
if hasattr(obj, 'child'):
for ch in obj.child:
printobj(ch, indent=indent+'')
def listd():
# retrieve and list
sess = Session()
print '# D-D'
query = sess.query(D).filter(D.id_d==None).order_by(D.name)
for dobj in query:
printobj(dobj)
sess.close()
def tst3():
# do stuff with self referential class D
sess = Session()
print #switch parentage of name 'd-two-child1' to 'd-one'
print '# before'
listd()
child = sess.query(D).filter(D.name=='d-two-child1').one()
parent = sess.query(D).filter(D.name=='d-one').one()
eng.echo=True
child.parent = parent
child.name += ' MOVED'
sess.commit()
eng.echo=False
print '# after'
listd()
initdb()
tst3()
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
On Jan 9, 10:03 pm, Darren Govoni dar...@ontrenet.com wrote:
Hi,
Thanks for the response. I'm still fairly new to SA but am very
impressed with this package!
I tried a variety of combinations of mappings. If I use just the
parent_id,parent it would seem to make sense logically if my children
only have one parent.
The tables generate fine. But when I try to set the parent of a child at
runtime it throws an exception about Conversion not being a list or
collection or something. So I was experimenting with the M2M, and as you
see, its not right.
Logically, the self referring parent should be enough I would think. Is
there another way using Base without having to use another mapping
technique since all my other classes are Base derived?
Thank you.
On Fri, 2009-01-09 at 20:17 -0500, Michael Bayer wrote:
On Jan 9, 2009, at 7:42 PM, project2501 wrote:
Hi,
I'm trying to create a mapped class that allows parent/child
relation of itself. I've spent the last 3 hours searching and reading
the other posts on this, but can't get anything to work.
I'm on 0.5rc4 and just want to declare this in a mapped class as such:
class Conversion(Base):
__tablename__ = 'conversion'
id = Column(Integer, primary_key=True)
name = Column(String(20))
parent_id =
[sqlalchemy] Re: Self-Referential Mapping with Base?
On Jan 9, 2009, at 7:42 PM, project2501 wrote:
Hi,
I'm trying to create a mapped class that allows parent/child
relation of itself. I've spent the last 3 hours searching and reading
the other posts on this, but can't get anything to work.
I'm on 0.5rc4 and just want to declare this in a mapped class as such:
class Conversion(Base):
__tablename__ = 'conversion'
id = Column(Integer, primary_key=True)
name = Column(String(20))
parent_id = Column(Integer, ForeignKey('conversion.id'))
parent = relation(Conversion, backref=child)
children = relation('Conversion', secondary=conversion_conversion,
backref='parents')
I was hoping to use the same style many-to-many declarations I do
elsewhere. It creates fine, but doesn't work when adding objects.
The many-to-many is possible but is not really necessary for the
typical self-referential mapping. It depends on if you'd like a
single object to have many parents. However in your example above, it
appears you are creating two separate self-referring bidirectional
relationships, parent/child (which is also misconfigured, the many-
to-one side needs a remote_side argument) and parents/children.
This would create two entirely isolated methods of associating one
Conversion object with another - there's no link between parent/child
and parents/children. Is this the desired effect ?
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[sqlalchemy] Re: Self-Referential Mapping with Base?
Hi,
Thanks for the response. I'm still fairly new to SA but am very
impressed with this package!
I tried a variety of combinations of mappings. If I use just the
parent_id,parent it would seem to make sense logically if my children
only have one parent.
The tables generate fine. But when I try to set the parent of a child at
runtime it throws an exception about Conversion not being a list or
collection or something. So I was experimenting with the M2M, and as you
see, its not right.
Logically, the self referring parent should be enough I would think. Is
there another way using Base without having to use another mapping
technique since all my other classes are Base derived?
Thank you.
On Fri, 2009-01-09 at 20:17 -0500, Michael Bayer wrote:
On Jan 9, 2009, at 7:42 PM, project2501 wrote:
Hi,
I'm trying to create a mapped class that allows parent/child
relation of itself. I've spent the last 3 hours searching and reading
the other posts on this, but can't get anything to work.
I'm on 0.5rc4 and just want to declare this in a mapped class as such:
class Conversion(Base):
__tablename__ = 'conversion'
id = Column(Integer, primary_key=True)
name = Column(String(20))
parent_id = Column(Integer, ForeignKey('conversion.id'))
parent = relation(Conversion, backref=child)
children = relation('Conversion', secondary=conversion_conversion,
backref='parents')
I was hoping to use the same style many-to-many declarations I do
elsewhere. It creates fine, but doesn't work when adding objects.
The many-to-many is possible but is not really necessary for the
typical self-referential mapping. It depends on if you'd like a
single object to have many parents. However in your example above, it
appears you are creating two separate self-referring bidirectional
relationships, parent/child (which is also misconfigured, the many-
to-one side needs a remote_side argument) and parents/children.
This would create two entirely isolated methods of associating one
Conversion object with another - there's no link between parent/child
and parents/children. Is this the desired effect ?
--~--~-~--~~~---~--~~
You received this message because you are subscribed to the Google Groups
sqlalchemy group.
To post to this group, send email to sqlalchemy@googlegroups.com
To unsubscribe from this group, send email to
sqlalchemy+unsubscr...@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/sqlalchemy?hl=en
-~--~~~~--~~--~--~---
[sqlalchemy] Re: Self-Referential Mapping with Base?
I spent some time understanding this a little while ago. Here is the
construct you need
(thanks to Michael Bayer for making it clear for me)
# D self referential
class D(Base):
__tablename__ = 'D'
id = Column(Integer, primary_key=True)
id_d = Column(Integer, ForeignKey('D.id'))
name = Column(Text)
child = relation('D', backref=backref('parent',
remote_side='D.id'))
The 'child' relation establishes the two way linkage you want.
One of the key things to think about is to use objects as normal
python data structures. Generally you don't need to manipulate ids;
let SQLAlchemy worry about that.
Here is sample script I used when learning the topic
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
from sqlalchemy import *
from sqlalchemy.orm import *
from sqlalchemy.ext.declarative import declarative_base
dbname = ''
dburl = 'sqlite:///%s' % dbname
# set up environment
eng = create_engine(dburl, echo=False)
meta = MetaData(bind=eng)
Base = declarative_base(metadata=meta)
Session = sessionmaker()
# D self referential
class D(Base):
__tablename__ = 'D'
id = Column(Integer, primary_key=True)
id_d = Column(Integer, ForeignKey('D.id'))
name = Column(Text)
child = relation('D',
backref=backref('parent', remote_side='D.id'))
def __repr__(self):
return '--D (id:%s-id_d:%s) %s --' % (self.id, self.id_d,
self.name)
def initdb():
print '# create the database'
meta.drop_all(checkfirst=True)
meta.create_all()
sess = Session()
# insert some data for self-reference relationship
for ddata in ('d-one', 'd-two'):
dobj = D(name=ddata)
sess.add(dobj)
dobj2 = D(name=ddata+'-child1')
dobj.child.append(dobj2)
dobj2 = D(name=ddata+'-child2')
dobj.child.append(dobj2)
dobj3 = D(name=ddata+'-child2'+'-child3')
dobj2.child.append(dobj3)
sess.commit()
sess.close()
def printobj(obj, indent=''):
# recursive list
print '%s%s' % (indent, obj)
if hasattr(obj, 'child'):
for ch in obj.child:
printobj(ch, indent=indent+'')
def listd():
# retrieve and list
sess = Session()
print '# D-D'
query = sess.query(D).filter(D.id_d==None).order_by(D.name)
for dobj in query:
printobj(dobj)
sess.close()
def tst3():
# do stuff with self referential class D
sess = Session()
print #switch parentage of name 'd-two-child1' to 'd-one'
print '# before'
listd()
child = sess.query(D).filter(D.name=='d-two-child1').one()
parent = sess.query(D).filter(D.name=='d-one').one()
eng.echo=True
child.parent = parent
child.name += ' MOVED'
sess.commit()
eng.echo=False
print '# after'
listd()
initdb()
tst3()
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
On Jan 9, 10:03 pm, Darren Govoni dar...@ontrenet.com wrote:
Hi,
Thanks for the response. I'm still fairly new to SA but am very
impressed with this package!
I tried a variety of combinations of mappings. If I use just the
parent_id,parent it would seem to make sense logically if my children
only have one parent.
The tables generate fine. But when I try to set the parent of a child at
runtime it throws an exception about Conversion not being a list or
collection or something. So I was experimenting with the M2M, and as you
see, its not right.
Logically, the self referring parent should be enough I would think. Is
there another way using Base without having to use another mapping
technique since all my other classes are Base derived?
Thank you.
On Fri, 2009-01-09 at 20:17 -0500, Michael Bayer wrote:
On Jan 9, 2009, at 7:42 PM, project2501 wrote:
Hi,
I'm trying to create a mapped class that allows parent/child
relation of itself. I've spent the last 3 hours searching and reading
the other posts on this, but can't get anything to work.
I'm on 0.5rc4 and just want to declare this in a mapped class as such:
class Conversion(Base):
__tablename__ = 'conversion'
id = Column(Integer, primary_key=True)
name = Column(String(20))
parent_id = Column(Integer, ForeignKey('conversion.id'))
parent = relation(Conversion, backref=child)
children = relation('Conversion', secondary=conversion_conversion,
backref='parents')
I was hoping to use the same style many-to-many declarations I do
elsewhere. It creates fine, but doesn't work when adding objects.
The many-to-many is possible but is not really necessary for the
typical self-referential mapping. It depends on if you'd like a
single object to have many parents. However in your example above, it
appears you are creating two separate self-referring bidirectional
relationships, parent/child (which is also misconfigured, the many-
to-one side needs a remote_side argument) and parents/children.
This would create two entirely isolated methods
