Contnuing your theme of each column being its own table - there is some sort of merit in thinking that way - at least initially. has ittle to do with rails of course, but just as a general framework of thought.
If you think conceptually about things that are hard to to in relational databases and things that are easy to do. It is, for example, much harder to add a new column than a new row to an exisiting database. So, if you have a very abstracted design like this.. Entity (entity id, entity name) Rowdata (rowdataid, domainid,entityid, colname,colvalue) Domain (domainid, domain_data_type) Then you could simply add new rows into the domain table and new rows into the Rowdata table every time you want to extend the schema. This of course is far too simplistic an approach - I have mixed the schema up with the values, so it is hopelessly unnormalized), but it sort of sets the mind off onto asking the questions about when we need ultimate flexibility vs when something just needs to work simply and quickly. The answers are never as simple as you think! However, I would also say, don't dwell on the "what might possible ne..." but implement what is most reasonable. Of course it is judgement, but when developing we always have to use our judgement. When we have made a design decision about such a thorny issue, document it so you don't have to revisit the reasons. You may have to revisit the decision, so it would be handy to know why the decision was made the way it was. I do have lots of rules (of thumb and otherwise) around this stuff - but that's how I make my living! http://businessanditarchitecture.blogspot.com C On Apr 14, 9:00 pm, Nik <niks...@gmail.com> wrote: > Thank you vERY much, Chris! -- One often has moments where he/she > notices something that may or may not be a real worry, but is too > doubtful to speak of it. I have each of your described considerations > pulsing through my head each time I think of the future of how these > models will be in case of modification or deletion, but it was too > vague as I had no substance to fill even a hypothetical example. But > your spelling them out certainly relieved me a little. > > Having been thinking of these (potential) problems, it compelled me to > think whether there's a kind of tutorial I can read up on some rules > of thumb of deciding if table or no table and so on. I thought, a few > days, ago, that in the worst case, if I made each column its own > table, a Phone Model, a Gender Model, an Areacode Model, etc, > basically every thing would have its own model, though unrealistically > complex, it'd work ( sort of conveying that the more orthogonal bases > you have, the better; in Linear Algebra). So building up a network of > tables each holding exactly one column, I was thinking that, some > empirical/theory-based rules for combining these hypothetical single > column tables. And your Socratic method (I hope I am using this phrase > right) isn't bad, at all. > > I will discuss with my supervisor for possible scenarios that call for > minor/major table alterations, then I will begin to ask these > questions myself :) > > Thanks again! > Thank you, everyone! > > On Apr 14, 11:16 am, Chris Bird <seabir...@gmail.com> wrote: > > > > > This is a specific case of a more general problem - how to manage > > inheritance in these kinds of models. There are several things to > > think about here. However they break down fairly easily. I'll use your > > specific example, but some of the observations might not make a whole > > lot of sense. So I will pose some questions and then give some guiding > > thinking. This will not be RAILS specific thinking, but bringing > > experience from enterprise class systems where we have things like > > this all the time. You can generalize the thinking questioning when > > the structures are even deeper. > > > Which attributes are common between Clients/Contractors? > > - If there are a lot of attributes in common you might get away with a > > single table, and a type field in the table. > > > Are there relationships identified that both Clients and Contractors > > can have? > > - If for example you had a security tag table and it needed to have > > the associated "person", and it doesn't matter if the person is a > > client or a contractor, then it might be worth managing that > > relationship via a separate table (a Person table). > > > Do you expect to add new kinds of things? > > - Are Clients and Contractors the only types of Persons? Will you need > > to add something else in the future - e.g. Overseas Contractor which > > is like a Contractor but has a bunch more fields, its own processes, > > screens, etc. If so you may want to break into multiple tables. > > > Do you expect to have a role concept that cuts across Clients/ > > Contractors? > > - Similar to relationships above, but let's imagine you also have > > roles like administrator, user, ... If those roles are independent of > > the Client/Contractor status, then again you might want separate > > tables. > > > Do you have to worry about history/transition? > > - If a Client can become a Contractor (or vice versa) - and you need > > to manage the history (for example if all the timesheets haven't been > > cleared yet), then you will have to have something a bit more complex. > > Now you have to manage the temporal element when the Person can be > > both. There are lots of ways of doing that, none of them ideal! > > > If you do decide to break into multiple tables, then make sure you > > manage the relationship handling among the tables inside the Model. Do > > not be tempted to put this into the Controller(s). Then you can treat > > the join of the Person with the Client or the Person with the > > Contractor as if they were individual Active Records. There will be > > performance penalties, but performance while important is not the only > > consideration. > > > Hope this helps > > > Chris > > > On Apr 10, 5:42 pm, Nik <niks...@gmail.com> wrote: > > > > Hello All, > > > > I have a User Model at the moment that has only username, password, > > > and roles. As you might guess, I can add to the User Model a phone > > > column which our clients have and our contractors also have. Many > > > other attributes may be share by both actually. But then only a client > > > can have a "rate" column, and a company association and other things. > > > And only a contractor can have, say, an internal FTP login/password > > > pair. > > > > I don't quite know the nature of rules on deciding just how I should > > > do about these un-shared attributes, I know that I use the "roles" > > > column to differentiate a client and a contractor (learned from Raile > > > Recipes); should I pool all attribute into User Model anyway and then > > > find a mechanism to permit/forbid a client to see the contractor only > > > attrib and vice versa? or two other tables one being > > > contractor_only_properties and the other client_only_properties? I > > > feel that having to build a table for each role seems a bit, I am very > > > unlikely to be right, inflexible or at least un-easily-extensible > > > (sorry for making words like this). > > > > Your (any) opinion is very valuable to me and I thank you for spending > > > your time reading my problem > > > > All my best, > > > Nik- Hide quoted text - > > - Show quoted text - --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Ruby on Rails: Talk" group. To post to this group, send email to rubyonrails-talk@googlegroups.com To unsubscribe from this group, send email to rubyonrails-talk+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/rubyonrails-talk?hl=en -~----------~----~----~----~------~----~------~--~---
