Mike, is the anti-pattern you mentioned possibly the nested sets of
naive trees?
On 01/17/2014 04:00 PM, Richard Gerd Kuesters wrote:
well ... let's go to the sql antipatterns book to see if i can find
this problem there ... :P
thanks a lot Mike.
best regards,
richard.
On 01/17/2014 03:42 PM, Michael Bayer wrote:
if you’re persisting to these tables outside of SQLAlchemy it might
be easier, not sure.
On Jan 17, 2014, at 12:37 PM, Richard Gerd Kuesters
<[email protected] <mailto:[email protected]>> wrote:
well, i have that feeling too. it's a basic NxN relationship between
the same instance type. the anti-pattern might be having a
polymorphic model to do that. i know sqlalchemy can handle this
issue and provide me constant results, but by hand it can give me
trouble ... should I remove the polymorphic association for logic' sake?
On 01/17/2014 03:24 PM, Michael Bayer wrote:
On Jan 17, 2014, at 12:05 PM, Richard Gerd Kuesters
<[email protected] <mailto:[email protected]>> wrote:
hi all,
I'm having a tricky situation while modeling a database here.
first, i'll just put the code of my two classes / models:
*
**class Resource(Base):**
**
** resource_id = Column(Integer, Sequence, primary_key=True)**
** resource_type_id = Column(Integer, ForeignKey(SomeClass.id),
nullable=False, index=True)**
** p_discriminator = Column(Integer)**
**
** __mapper_args__ = dict(**
**polymorphic_on=p_discriminator,**
** polymorphic_identity=1**
** )**
**
**class ResourceRelationship(Resource):**
**
** resource_id = Column(Integer,
ForeignKey(Resource.resource_id), primary_key=True, index=True)**
** left_resource_id = Column(Integer,
ForeignKey(Resource.resource_id), nullable=True, index=True)**
** right_resource_id = Column(Integer,
ForeignKey(Resource.resource_id), nullable=True, index=True)**
**
** __mapper_args__ = dict(**
** polymorphic_identity=2**
**inherit_condition=(resource_id == Resource.resource_id)**
** )*
ok, nothing fancy but, I would really like to create a unique
constraint on ResourceRelationship, using left_resouce_id,
right_resource_id AND the inherited resource_type_id.
the problem is: i can do that only using concrete inheritance,
afaik. i would not like to do that because i really like the way
polymorphic models work -- and the most important reason: this
database is shared with other applications that would not rely on
sqlalchemy to do the magic of maintain the data integrity.
you’d need to add resource_type_id to ResourceRelationship as well.
The SQLAlchemy mapping will maintain the same value for both
columns provided you map them under the same attribute name.
i have a sneaky feeling there’s some relational design antipattern
occurring here but I’m not adept enough to determine specifically
what that might be.
--
You received this message because you are subscribed to the Google
Groups "sqlalchemy" group.
To unsubscribe from this group and stop receiving emails from it,
send an email to [email protected]
<mailto:[email protected]>.
To post to this group, send email to [email protected]
<mailto:[email protected]>.
Visit this group at http://groups.google.com/group/sqlalchemy.
For more options, visit https://groups.google.com/groups/opt_out.
--
You received this message because you are subscribed to the Google
Groups "sqlalchemy" group.
To unsubscribe from this group and stop receiving emails from it, send
an email to [email protected].
To post to this group, send email to [email protected].
Visit this group at http://groups.google.com/group/sqlalchemy.
For more options, visit https://groups.google.com/groups/opt_out.
--
You received this message because you are subscribed to the Google Groups
"sqlalchemy" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to [email protected].
To post to this group, send email to [email protected].
Visit this group at http://groups.google.com/group/sqlalchemy.
For more options, visit https://groups.google.com/groups/opt_out.
