[sqlalchemy] Re: a-directional i.e. bi-directional m:m relations
Thanks for the ideas. I thought of all of the above. The one I've been using is the accessor which unions together the necessary things. My question came up when I wondered if there was some even more fundamental way to handle these forwards-backwards cases. I'm glad to know I'm already doing all I can. On Dec 2, 3:32 pm, Michael Bayer [EMAIL PROTECTED] wrote: On Dec 2, 2008, at 5:54 PM, Eric Ongerth wrote: Now when I want to find out whether a Foo has a relation to another Foo, I have to check whether there exists any row in foo_relations that has the given Foo as either as this OR that. Also, what if I need backrefs on the foo_relations mapper? The backref from 'this' and the backref from 'that' would both point to something called a foo, but they would have to be given separate labels in order ot not be conflicting property names -- when really, I would not want to know if a foo was the 'that' or the 'this' of some foo relation. So ideally in a case like this, I could set an option that says the m:m relation is bidirectional, and that the backrefs for both foreign keys in the m:m table should really point to the same place (or at least be unioned together). I have a feeling that would violate some part of the RDBMS standards, and I'm perfectly willing to go without or work around. This is more of a philosophical point for learning's sake -- what do other people do in such cases? you can store two rows in the association table, one for each direction. or provide an accessor which just unions together the forwards and backwards references between Foo objects. or make a readonly relation() that does the appropriate OR logic. I might even try combining both of those techniques somehow. --~--~-~--~~~---~--~~ 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: a-directional i.e. bi-directional m:m relations
there is... u do not want to know if A points B or B points A, u want to know if A and B are related in whatever aspect. That is, A and B are members of some set X denoting that aspect. i.e. moving the belonginess out of A and B alltogether. but this isn't going to make your DB simpler... quite the opposite. On Friday 05 December 2008 10:40:16 Eric Ongerth wrote: Thanks for the ideas. I thought of all of the above. The one I've been using is the accessor which unions together the necessary things. My question came up when I wondered if there was some even more fundamental way to handle these forwards-backwards cases. I'm glad to know I'm already doing all I can. On Dec 2, 3:32 pm, Michael Bayer [EMAIL PROTECTED] wrote: On Dec 2, 2008, at 5:54 PM, Eric Ongerth wrote: Now when I want to find out whether a Foo has a relation to another Foo, I have to check whether there exists any row in foo_relations that has the given Foo as either as this OR that. Also, what if I need backrefs on the foo_relations mapper? The backref from 'this' and the backref from 'that' would both point to something called a foo, but they would have to be given separate labels in order ot not be conflicting property names -- when really, I would not want to know if a foo was the 'that' or the 'this' of some foo relation. So ideally in a case like this, I could set an option that says the m:m relation is bidirectional, and that the backrefs for both foreign keys in the m:m table should really point to the same place (or at least be unioned together). I have a feeling that would violate some part of the RDBMS standards, and I'm perfectly willing to go without or work around. This is more of a philosophical point for learning's sake -- what do other people do in such cases? you can store two rows in the association table, one for each direction. or provide an accessor which just unions together the forwards and backwards references between Foo objects. or make a readonly relation() that does the appropriate OR logic. I might even try combining both of those techniques somehow. --~--~-~--~~~---~--~~ 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: a-directional i.e. bi-directional m:m relations
Oh, right. I don't know what type of brain fog obscured that basic relational fact, except that I may have been burning my synapses a bit too hot lately resulting in a deplorable deficit of neurotransmitters. Thank you for helping me regain the sight of the obvious. On Dec 5, 1:16 am, [EMAIL PROTECTED] wrote: there is... u do not want to know if A points B or B points A, u want to know if A and B are related in whatever aspect. That is, A and B are members of some set X denoting that aspect. i.e. moving the belonginess out of A and B alltogether. but this isn't going to make your DB simpler... quite the opposite. On Friday 05 December 2008 10:40:16 Eric Ongerth wrote: Thanks for the ideas. I thought of all of the above. The one I've been using is the accessor which unions together the necessary things. My question came up when I wondered if there was some even more fundamental way to handle these forwards-backwards cases. I'm glad to know I'm already doing all I can. On Dec 2, 3:32 pm, Michael Bayer [EMAIL PROTECTED] wrote: On Dec 2, 2008, at 5:54 PM, Eric Ongerth wrote: Now when I want to find out whether a Foo has a relation to another Foo, I have to check whether there exists any row in foo_relations that has the given Foo as either as this OR that. Also, what if I need backrefs on the foo_relations mapper? The backref from 'this' and the backref from 'that' would both point to something called a foo, but they would have to be given separate labels in order ot not be conflicting property names -- when really, I would not want to know if a foo was the 'that' or the 'this' of some foo relation. So ideally in a case like this, I could set an option that says the m:m relation is bidirectional, and that the backrefs for both foreign keys in the m:m table should really point to the same place (or at least be unioned together). I have a feeling that would violate some part of the RDBMS standards, and I'm perfectly willing to go without or work around. This is more of a philosophical point for learning's sake -- what do other people do in such cases? you can store two rows in the association table, one for each direction. or provide an accessor which just unions together the forwards and backwards references between Foo objects. or make a readonly relation() that does the appropriate OR logic. I might even try combining both of those techniques somehow. --~--~-~--~~~---~--~~ 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: a-directional i.e. bi-directional m:m relations
On Dec 2, 2008, at 5:54 PM, Eric Ongerth wrote: Now when I want to find out whether a Foo has a relation to another Foo, I have to check whether there exists any row in foo_relations that has the given Foo as either as this OR that. Also, what if I need backrefs on the foo_relations mapper? The backref from 'this' and the backref from 'that' would both point to something called a foo, but they would have to be given separate labels in order ot not be conflicting property names -- when really, I would not want to know if a foo was the 'that' or the 'this' of some foo relation. So ideally in a case like this, I could set an option that says the m:m relation is bidirectional, and that the backrefs for both foreign keys in the m:m table should really point to the same place (or at least be unioned together). I have a feeling that would violate some part of the RDBMS standards, and I'm perfectly willing to go without or work around. This is more of a philosophical point for learning's sake -- what do other people do in such cases? you can store two rows in the association table, one for each direction. or provide an accessor which just unions together the forwards and backwards references between Foo objects. or make a readonly relation() that does the appropriate OR logic. I might even try combining both of those techniques somehow. --~--~-~--~~~---~--~~ 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 -~--~~~~--~~--~--~---
