no, 2 tables, plants and characteristics and 2 join tables for the provides and needs relationships
On Jun 2, 3:54 am, Ronbo <[email protected]> wrote: > Thanks Kevin, > > I'm still not clear on this. You mentioned below that I'd need three > tables in addition to 'plant', but I see: > > plant, characteristic, provides, needs, provides_characteristics, and > needs_characteristics. Am I right that this means that each > characteristic must be duplicated for the provides and needs > relationships it will have with 'plant' and their is no way of keying > two relationships with plant off the same table? > > On Jun 1, 5:33 pm, kevinpfromnm <[email protected]> wrote: > > > it sounds like what you are describing would need 3 additional tables > > in addition to the plants table. > > plant > > > characteristic > > > provides join > > needs join > > > plant has many provides_characteristics and many provides through > > provides characteristics > > plant has many needs characteristics and many needs through needs > > characteristics > > > then you can start looking at a characteristic and seeing what plants > > have and need it relatively easily. otherwise, you can add a flag on > > a single join table that tells whether it's a provides or a needs... I > > think the 4 table approach though will be easier to write views and > > such for as there is a clear functional division between the provides > > and needs relationships, even if the data difference is negligible. > > > On Jun 1, 2:40 pm, Ronbo <[email protected]> wrote: > > > > Hello, > > > > I have a beginner's question about modeling. The application I am > > > working on is a plant database. One of the critical features is that > > > it make it easy to represent symbiotic relationships (like the 3 > > > sisters in Mexico, squash, beans and corn), and to discover potential > > > new relationships. > > > > So I have a plant model with some core characteristics describing a > > > species. I would like to be able to assign certain attributes by which > > > a plant has relationships with other species, such as: > > > > shade > > > fixes_nitrogen > > > scaffolding (corn provides a scaffold for beans to climb) > > > Micronutrients > > > etc. > > > > These would be another table. > > > So far, easy. > > > > Plants can have one of two types of relationships with these > > > characteristics. Either 'need' or 'provide'. So a plant could provide > > > shade and need scaffolding, while another needs shade and provides > > > scaffolding... > > > > Question: can this be represented with just two tables, and if so, how > > > to go about it, or do I need to duplicate these characteristics in > > > 'needs' and 'provides' tables? From the little I know about > > > polymorphic associations, this seems different. > > > > Many thanks > > -- You received this message because you are subscribed to the Google Groups "Hobo Users" 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/hobousers?hl=en.
