2008/8/28 Michael Bayer <[EMAIL PROTECTED]>: > > > On Aug 28, 2008, at 8:11 AM, Cecil Westerhof wrote: > >> >> I was just wondering if the folowing possible. >> >> A record has severall groups connected through a N:M relation. >> But it also has a parent. What I would like is that all the groups >> from the parent (and its parent, etc.) also are seen as group for the >> record. >> When the parent has a group added or removed that should then be >> 'visible' at the child. >> Not a very good description I am afraid, so I'll try to give an >> example. >> >> Say I have the groups G1, G2, G3, G4 and G5. >> I have the records R1 and R2. R1 is the parent of R2 and does not have >> a parent itself. >> >> If R1 has the groups G1 and G2 and R2 has the groups G2, G4 and G5, >> then when asking the list of groups of R2 should give, G1, G2, G4 and >> G5. >> When quering for records that have group G1, both R1 and R2 should >> be returned. >> >> When adding G3 to R1 the list for R2 should be: G1, G2, G3, G4 and G5. >> When removing G1 from R1 the list for R2 should be: G2, G3, G4 and G5. >> When removing G2 from R1 the list for R2 should be: G2, G3, G4 and G5. >> (R2 has itself also group G2.) >> >> Is this possible with sqlalchemy or has this to be done by hand? > > I wouldn't say "by hand". An element's groups are basically its own > groups unioned with the groups of its parent. So a simple recursion > is the simplest way to form this group, but this only handles the > "object graph" side of the equation, not the "Query" side.
Thanks for the info. I'll have to digest it, because I am just starting with sqlalchemy. But it is nice to know that I could implement this functionality. > On the Query side, the basic job is to formulate joins to the parent, Would it no be better to the child? Otherwise you need to traverse all records, which would be inefficient -I think- when for example only 1% of the records are in the group. Or am I overlooking something? -- Cecil Westerhof --~--~---------~--~----~------------~-------~--~----~ 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 -~----------~----~----~----~------~----~------~--~---
