[sqlalchemy] Re: One To Many Polymorphic Association.
On Monday 27 August 2007 19:57:21 Michael Bayer wrote:
On Aug 24, 2007, at 8:39 AM, praddy wrote:
##
from sqlalchemy import *
meta = BoundMetaData('sqlite://', echo=False)
# Parents table.
parents = Table('parents', meta,
Column(id, Integer, primary_key=True),
Column(data, String(50), nullable=False)
)
# Children_1 Table.
children_1 = Table('children_1', meta,
Column(id, Integer, primary_key=True),
Column(data, String(50), nullable=False)
)
# Children_2 Table.
children_2 = Table('children_2', meta,
Column(id, Integer, primary_key=True),
Column(data, String(50))
)
# Association Table.
# This is a generic table which can relate anything to parent.
assoc = Table('assoc', meta,
# parents.c.id
Column(parent_id, Integer, ForeignKey(parents.c.id)),
# associate's id either children_1.c.id or children_2.c.id or any
other child.
Column(assoc_id, Integer),
# Which can be either 'child_1' or 'child_2' for now (can be used for
extending children
# type, decides which table to look in.
Column(assoc_type, String(20))
)
###
I am a novice with respect to sqlalchemy may be RDBMS as well.
How would you like to work on this scenario to achieve backwards
cascading (may not be the right word) which means when one deletes
one specific child from children_1 table (for example), there should
not be any
association entry, which associates that child to the parent, in the
association table as well?
To allow proper foreign key support, you probably want to place the
foreign key to the association table on each of children_1 and
children_2, and remove the assoc_id column from the assoc table.
this is the key to the blog article about polymorphic associations.
its probably easiest for you to work with the example mentioned in
the blog and modify. (http://techspot.zzzeek.org/files/
poly_assoc_2.py ). at least, if you study the example it will lead
to more insight on how to approach this. If you really want to keep
your foreign keys as they are, the ActiveRecord example (http://
techspot.zzzeek.org/files/poly_assoc_1.py ) illustrates that pattern
with SA.
next, you're going to want to specify cascade='all, delete-orphan'
on both relations which reference the association table:
mapper(Parent, parents, properties={
'associations':relation(Association, cascade=all, delete-orphan)
})
class Association(object):
def _child(self):
if self.assoc_type='child1':
return self.child_1
else:
return self.child_2
child=property(_child)
mapper(Association, assoc, properties={
'child_1':relation(Child1, backref=backref(assoc_1,
cascade=all, delete-orphan)),
'child_2':relation(Child2, backref=backref(assoc_2,
cascade=all, delete-orphan)),
})
mapper(Child1, children_1)
mapper(Child2, children_2)
im out of town this week so I dont have the resources to work out the
full solution but this is the general idea.
Mike,
I have got the solution this way.
- Pradeep Jindal
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poly_assoc_sep_table.py
Description: application/python
[sqlalchemy] Re: One To Many Polymorphic Association.
Currently, unable to find any solution for this problem. I think my
little knowledge with respect to
sqlalchemy is restricting me to get a solution for this issue. Anyone
with somewhat more in-depth
knowledge should be able to find a solution.
Waiting...
Regards,
Pradeep Jindal
On Aug 25, 1:15 am, Pradeep Jindal [EMAIL PROTECTED] wrote:
On Friday 24 August 2007 19:20:00 Gaetan de Menten wrote:
You might be interested by:http://techspot.zzzeek.org/?p=13
(also in the examples directory of SQLAlchemy)
On 8/24/07, praddy [EMAIL PROTECTED] wrote:
##
from sqlalchemy import *
meta = BoundMetaData('sqlite://', echo=False)
# Parents table.
parents = Table('parents', meta,
Column(id, Integer, primary_key=True),
Column(data, String(50), nullable=False)
)
# Children_1 Table.
children_1 = Table('children_1', meta,
Column(id, Integer, primary_key=True),
Column(data, String(50), nullable=False)
)
# Children_2 Table.
children_2 = Table('children_2', meta,
Column(id, Integer, primary_key=True),
Column(data, String(50))
)
# Association Table.
# This is a generic table which can relate anything to parent.
assoc = Table('assoc', meta,
# parents.c.id
Column(parent_id, Integer, ForeignKey(parents.c.id)),
# associate's id either children_1.c.id or children_2.c.id or any
other child.
Column(assoc_id, Integer),
# Which can be either 'child_1' or 'child_2' for now (can be used
for extending children
# type, decides which table to look in.
Column(assoc_type, String(20))
)
###
I am a novice with respect to sqlalchemy may be RDBMS as well.
How would you like to work on this scenario to achieve backwards
cascading (may not be the right word) which means when one deletes
one specific child from children_1 table (for example), there should
not be any
association entry, which associates that child to the parent, in the
association table as well?
Thanks for the reply. I have already gone through that article, but was unable
to figure out the solution. Anyways, I will give it one more try. Please note
that this scenario is already there and I can't make any changes to the
tables at all.
Thanks
- Pradeep Jindal
--~--~-~--~~~---~--~~
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 [EMAIL PROTECTED]
For more options, visit this group at
http://groups.google.com/group/sqlalchemy?hl=en
-~--~~~~--~~--~--~---
[sqlalchemy] Re: One To Many Polymorphic Association.
On Aug 24, 2007, at 8:39 AM, praddy wrote:
##
from sqlalchemy import *
meta = BoundMetaData('sqlite://', echo=False)
# Parents table.
parents = Table('parents', meta,
Column(id, Integer, primary_key=True),
Column(data, String(50), nullable=False)
)
# Children_1 Table.
children_1 = Table('children_1', meta,
Column(id, Integer, primary_key=True),
Column(data, String(50), nullable=False)
)
# Children_2 Table.
children_2 = Table('children_2', meta,
Column(id, Integer, primary_key=True),
Column(data, String(50))
)
# Association Table.
# This is a generic table which can relate anything to parent.
assoc = Table('assoc', meta,
# parents.c.id
Column(parent_id, Integer, ForeignKey(parents.c.id)),
# associate's id either children_1.c.id or children_2.c.id or any
other child.
Column(assoc_id, Integer),
# Which can be either 'child_1' or 'child_2' for now (can be used for
extending children
# type, decides which table to look in.
Column(assoc_type, String(20))
)
###
I am a novice with respect to sqlalchemy may be RDBMS as well.
How would you like to work on this scenario to achieve backwards
cascading (may not be the right word) which means when one deletes
one specific child from children_1 table (for example), there should
not be any
association entry, which associates that child to the parent, in the
association table as well?
To allow proper foreign key support, you probably want to place the
foreign key to the association table on each of children_1 and
children_2, and remove the assoc_id column from the assoc table.
this is the key to the blog article about polymorphic associations.
its probably easiest for you to work with the example mentioned in
the blog and modify. (http://techspot.zzzeek.org/files/
poly_assoc_2.py ). at least, if you study the example it will lead
to more insight on how to approach this. If you really want to keep
your foreign keys as they are, the ActiveRecord example (http://
techspot.zzzeek.org/files/poly_assoc_1.py ) illustrates that pattern
with SA.
next, you're going to want to specify cascade='all, delete-orphan'
on both relations which reference the association table:
mapper(Parent, parents, properties={
'associations':relation(Association, cascade=all, delete-orphan)
})
class Association(object):
def _child(self):
if self.assoc_type='child1':
return self.child_1
else:
return self.child_2
child=property(_child)
mapper(Association, assoc, properties={
'child_1':relation(Child1, backref=backref(assoc_1,
cascade=all, delete-orphan)),
'child_2':relation(Child2, backref=backref(assoc_2,
cascade=all, delete-orphan)),
})
mapper(Child1, children_1)
mapper(Child2, children_2)
im out of town this week so I dont have the resources to work out the
full solution but this is the general idea.
--~--~-~--~~~---~--~~
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 [EMAIL PROTECTED]
For more options, visit this group at
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-~--~~~~--~~--~--~---
[sqlalchemy] Re: One To Many Polymorphic Association.
On Monday 27 August 2007 19:57:21 Michael Bayer wrote:
On Aug 24, 2007, at 8:39 AM, praddy wrote:
##
from sqlalchemy import *
meta = BoundMetaData('sqlite://', echo=False)
# Parents table.
parents = Table('parents', meta,
Column(id, Integer, primary_key=True),
Column(data, String(50), nullable=False)
)
# Children_1 Table.
children_1 = Table('children_1', meta,
Column(id, Integer, primary_key=True),
Column(data, String(50), nullable=False)
)
# Children_2 Table.
children_2 = Table('children_2', meta,
Column(id, Integer, primary_key=True),
Column(data, String(50))
)
# Association Table.
# This is a generic table which can relate anything to parent.
assoc = Table('assoc', meta,
# parents.c.id
Column(parent_id, Integer, ForeignKey(parents.c.id)),
# associate's id either children_1.c.id or children_2.c.id or any
other child.
Column(assoc_id, Integer),
# Which can be either 'child_1' or 'child_2' for now (can be used for
extending children
# type, decides which table to look in.
Column(assoc_type, String(20))
)
###
I am a novice with respect to sqlalchemy may be RDBMS as well.
How would you like to work on this scenario to achieve backwards
cascading (may not be the right word) which means when one deletes
one specific child from children_1 table (for example), there should
not be any
association entry, which associates that child to the parent, in the
association table as well?
To allow proper foreign key support, you probably want to place the
foreign key to the association table on each of children_1 and
children_2, and remove the assoc_id column from the assoc table.
this is the key to the blog article about polymorphic associations.
its probably easiest for you to work with the example mentioned in
the blog and modify. (http://techspot.zzzeek.org/files/
poly_assoc_2.py ). at least, if you study the example it will lead
to more insight on how to approach this. If you really want to keep
your foreign keys as they are, the ActiveRecord example (http://
techspot.zzzeek.org/files/poly_assoc_1.py ) illustrates that pattern
with SA.
next, you're going to want to specify cascade='all, delete-orphan'
on both relations which reference the association table:
mapper(Parent, parents, properties={
'associations':relation(Association, cascade=all, delete-orphan)
})
class Association(object):
def _child(self):
if self.assoc_type='child1':
return self.child_1
else:
return self.child_2
child=property(_child)
mapper(Association, assoc, properties={
'child_1':relation(Child1, backref=backref(assoc_1,
cascade=all, delete-orphan)),
'child_2':relation(Child2, backref=backref(assoc_2,
cascade=all, delete-orphan)),
})
mapper(Child1, children_1)
mapper(Child2, children_2)
im out of town this week so I dont have the resources to work out the
full solution but this is the general idea.
Michael,
Thanks for the reply. I think I already got the solution, I will post
it here
after the testing part of it. Further, I could not change any table in the
real scenario, I had to go with the existing tables.
Thanks again.
Pradeep Jindal
--~--~-~--~~~---~--~~
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 [EMAIL PROTECTED]
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-~--~~~~--~~--~--~---
[sqlalchemy] Re: One To Many Polymorphic Association.
You might be interested by: http://techspot.zzzeek.org/?p=13
(also in the examples directory of SQLAlchemy)
On 8/24/07, praddy [EMAIL PROTECTED] wrote:
##
from sqlalchemy import *
meta = BoundMetaData('sqlite://', echo=False)
# Parents table.
parents = Table('parents', meta,
Column(id, Integer, primary_key=True),
Column(data, String(50), nullable=False)
)
# Children_1 Table.
children_1 = Table('children_1', meta,
Column(id, Integer, primary_key=True),
Column(data, String(50), nullable=False)
)
# Children_2 Table.
children_2 = Table('children_2', meta,
Column(id, Integer, primary_key=True),
Column(data, String(50))
)
# Association Table.
# This is a generic table which can relate anything to parent.
assoc = Table('assoc', meta,
# parents.c.id
Column(parent_id, Integer, ForeignKey(parents.c.id)),
# associate's id either children_1.c.id or children_2.c.id or any
other child.
Column(assoc_id, Integer),
# Which can be either 'child_1' or 'child_2' for now (can be used for
extending children
# type, decides which table to look in.
Column(assoc_type, String(20))
)
###
I am a novice with respect to sqlalchemy may be RDBMS as well.
How would you like to work on this scenario to achieve backwards
cascading (may not be the right word) which means when one deletes
one specific child from children_1 table (for example), there should
not be any
association entry, which associates that child to the parent, in the
association table as well?
--
Gaëtan de Menten
http://openhex.org
--~--~-~--~~~---~--~~
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 [EMAIL PROTECTED]
For more options, visit this group at
http://groups.google.com/group/sqlalchemy?hl=en
-~--~~~~--~~--~--~---
[sqlalchemy] Re: One To Many Polymorphic Association.
On Friday 24 August 2007 19:20:00 Gaetan de Menten wrote:
You might be interested by: http://techspot.zzzeek.org/?p=13
(also in the examples directory of SQLAlchemy)
On 8/24/07, praddy [EMAIL PROTECTED] wrote:
##
from sqlalchemy import *
meta = BoundMetaData('sqlite://', echo=False)
# Parents table.
parents = Table('parents', meta,
Column(id, Integer, primary_key=True),
Column(data, String(50), nullable=False)
)
# Children_1 Table.
children_1 = Table('children_1', meta,
Column(id, Integer, primary_key=True),
Column(data, String(50), nullable=False)
)
# Children_2 Table.
children_2 = Table('children_2', meta,
Column(id, Integer, primary_key=True),
Column(data, String(50))
)
# Association Table.
# This is a generic table which can relate anything to parent.
assoc = Table('assoc', meta,
# parents.c.id
Column(parent_id, Integer, ForeignKey(parents.c.id)),
# associate's id either children_1.c.id or children_2.c.id or any
other child.
Column(assoc_id, Integer),
# Which can be either 'child_1' or 'child_2' for now (can be used
for extending children
# type, decides which table to look in.
Column(assoc_type, String(20))
)
###
I am a novice with respect to sqlalchemy may be RDBMS as well.
How would you like to work on this scenario to achieve backwards
cascading (may not be the right word) which means when one deletes
one specific child from children_1 table (for example), there should
not be any
association entry, which associates that child to the parent, in the
association table as well?
Thanks for the reply. I have already gone through that article, but was unable
to figure out the solution. Anyways, I will give it one more try. Please note
that this scenario is already there and I can't make any changes to the
tables at all.
Thanks
- Pradeep Jindal
--~--~-~--~~~---~--~~
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 [EMAIL PROTECTED]
For more options, visit this group at
http://groups.google.com/group/sqlalchemy?hl=en
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