On Jan 10, 2010, at 2:55 PM, Jules Stevenson wrote: > Sorry for the bad subject, and probably incorrect terminology but is > it possible to set up a table that would allow a foreign key link (or > any other technique) that would enable it to bind against *any* other > mapped class? > > The context for this is there is a DB table that stores tasks to be > executed. These tasks could relate to lots and lots of other mapped > classes, and essentially I'd just like to be able to call: > > sentinelTask.dbObject > > where dbObject could be a user, project, client or any other allready > mapped class. > > Is this possible? What should the DB structure be to set this sort of > relationship up. > > Sorry if this is just plain stupid, any pointers much appreciated.
In order from easiest to most tedious: method 1: - put individual foreign key columns on "task" relating to each kind of target object. On your class, "dbObject" just checks each of the related attributes for non-None, then returns that. method 2: - user, project client etc. all have a foreign key back to your "task" table, not the other way around. As before "dbObject" checks among several related attributes. method 3: - use an association table for each association of "task" to "X". The basic idea of this is described at http://techspot.zzzeek.org/?p=13 . The examples there use an older style of SQLA querying but are easy to update. method 4: - user, project, client etc. are all inherited from a "base" table, and your task table contains a foreign key to that. See the docs on joined table inheritance for that. If you're already using "joined" then this would be the easiest method. > > Jules > -- > You received this message because you are subscribed to the Google Groups > "sqlalchemy" group. > To post to this group, send email to sqlalch...@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. > >
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