On Wed, Jul 1, 2009 at 10:07, <[email protected]> wrote: > On Tue, Jun 30, 2009 at 13:32, Gaetan de Menten<[email protected]> wrote: >> >> I'm faced with a tough decision. Here is the problem: the way Elixir >> generates/uses column names for bidirectional (ie where an inverse >> exist), self-referencial ManyToMany relationships is buggy. To make >> sure, here is an example of what I'm talking about: >> > in this example: >> >> class Person(Entity): >> using_options(shortnames=True) >> parents = ManyToMany('Person') >> children = ManyToMany('Person') >> >> Currently, it uses the following pattern for the columns of *all* >> ManyToMany relationships: >> >> "%(tablename)s_%(key)s"
> %(tablename)s_%(relationshipname) This is exactly what I proposed in solution #1. >> In case the relationship is self-referential, it adds the "appearance >> number" of the relationship (ie 1 for the first relationship declared, >> and 2 for the inverse). > i understand this should be the backward compatible solution, perharps with > a tableoption, or a global M2M flag. Whatever scheme is implemented, it is my intention to also implement a global switch you can turn on to get the old behavior. The thing is you'll have to switch it on. But the applications will break if the user has not turned that switch on (or otherwise updated his code/DB). >> To illustrate this, the above example would generate a table with the >> following columns: person_id1 and person_id2, the first one being used >> by the "parents" side, while the second one is used for the "children" >> side. The problem is that if you inverse the order of declaration of >> those fields, the generated columns are the same but are used by the >> other side of the relationship. In other words, the meaning of the >> relationship is reversed. >> >> Here are the solutions I could come up: >> >> 1) Produce column names which depend on the relation name for all >> ManyToMany relationships. >> >> Pro: >> - Seems logical. This is the pattern I wish I had used in the first >> place. >> >> Con: >> - Massive breakage when upgrading from older Elixir: all ManyToMany >> (self-referencial or not) relationships are affected. That is, each >> developer will need to either: >> * use old scheme through setting the global variable >> "elixir.M2MCOL_NAMEFORMAT" before doing anything else with Elixir. >> Ugly but effective. >> * use local_colname AND remote_colname in every ManyToMany >> relationship. >> * update all M2M tables >> - We cannot easily detect (at Elixir-level) whether there is a >> problem or not and thus provide "migration help" automatically. That >> is, people upgrading without reading the release/upgrade notes (and >> unfortunately I think most people don't) will be hit by strange >> "missing column" errors without any clear indication of what to do to >> fix the problem. >> - Breaks if the relationship is renamed. This seems logical and IMO >> acceptable. In that case, the developer can simply use local_colname >> for the renamed relationship. >> >> -- Gaëtan de Menten http://openhex.org --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "SQLElixir" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/sqlelixir?hl=en -~----------~----~----~----~------~----~------~--~---
