Iceman, In a perfect wolrd there would never be a need to create an artificial primary key. However once people start using the applications things tend to get messier.
Using your example, what happens when the student changes majors or enters a post graduate degree and his ID changes to refelct the deparetment change. If you have foreign key references on that logical primary key you have a problem. Even if the business logic states the ID should never change, people make mistakes so you still need to be able to change that field. There can also be a matter of performace. There is no faster index than an integer. So forcing your database to use a logical primary key (or composite key) can hinder database performance depending on your situation. Nathan On 12/15/08, Ice-Man <[email protected]> wrote: > I strongly DESAGREE u. Acording Data Modeling (entity-relation modeling) > there isn't any reason to create an ARTIFICAL IDENTIFIER ATTRIBUTE, if there > is a REAL data that can be used as the identifier. > Otherwise u may designate a artifical identifier. Pupils from Colleges > Applicants use to be an anagrama of letters and numbers (so that make up > ID). I think u guess what I mean. > > Gupta, > > But, I think it's almost impossible to set Hibernate to generate such ID > in automatic fashion. It's better to generate that ID by your application > and set Hibernate so that. I think that's the simplest way. > Hope helping, > > Ice-Man > > 2008/12/15 Nathan Anderson <[email protected]> > >> Just like Oscar stated, it is generally considered a best practice to have >> database primary keys that have no business meaning attached to them. The >> example you provide appears as though it probably should be defined as a >> unique not null column, but not primary key. But even if you change the >> data structure that doesn't solve the problem of auto assigning the "next" >> value to a new record. >> >> The method I have used in the past for situations like this to have a >> table >> in the database that holds the "next" value. Then update the value >> database >> either in a transaction from your application, or in a stored procedure >> used >> to save a new record, or with a trigger on the insert statement. >> >> Hope that helps, >> Nathan >> >> >> >> On Sun, Dec 14, 2008 at 8:51 PM, sudhakargupta < >> [email protected]> wrote: >> >>> >>> Thanks for your reply and i need an id likes the 05-CS-123 so, i need an >>> auto >>> generated string to increment the last number, if the client want to use >>> the >>> assigned then how to mention in model class to assign the @Id value. >>> >>> >>> Sudhakar >>> >>> >>> Oscar Alvarez-2 wrote: >>> > >>> > Hello, >>> > >>> > What's the diference between autogenerated Long key and autogenerated >>> > String >>> > key???, i mean, if the String is autogenerated, it's not better >>> > solution >>> a >>> > Long key?, but if the String key is meaningful for the end user, then >>> you >>> > should define assigned strategy and assign it before save. >>> > >>> > Best Regards >>> > >>> > >>> > >>> > 2008/12/13 sudhakargupta <[email protected]> >>> > >>> >> >>> >> Thanks for your reply >>> >> >>> >> Is there any other way to use the auto generator for the string in >>> mysql >>> >> or in any other database >>> >> >>> >> please suggest me for this solution.. >>> >> >>> >> Sudhakar.. >>> >> >>> >> >>> >> >>> >> mraible wrote: >>> >> > >>> >> > If you're going to use Strings for the primary key, you'll have to >>> use >>> >> > a type of generator that doesn't increment. I've never done this, >>> >> > hopefully someone else on this list can help you. >>> >> > >>> >> > Matt >>> >> > >>> >> > On Fri, Dec 12, 2008 at 5:39 AM, sudhakargupta >>> >> > <[email protected]> wrote: >>> >> >> >>> >> >> Hi Matt... >>> >> >> >>> >> >> >>> >> >> Presently i'm working with the appfuse2 struts.. In one of my >>> >> >> table >>> i >>> >> >> need >>> >> >> to use the String as a primarykey and use foreignkey relations with >>> >> this >>> >> >> primarykey. >>> >> >> >>> >> >> i created a model class primary key setters/getters are >>> >> >> >>> >> >> >>> >> >> @Id >>> >> >> private String code; >>> >> >> >>> >> >> private String getCode() { >>> >> >> return this.code; >>> >> >> } >>> >> >> >>> >> >> private void setCode(String code) { >>> >> >> this.code = code; >>> >> >> } >>> >> >> >>> >> >> and after that run the command like mvn appfuse:gen and creates the >>> >> all >>> >> >> the >>> >> >> action classes and the jsp files. after that run the command like >>> mvn >>> >> >> jetty:run, then it shows the errors to create the database and to >>> run >>> >> the >>> >> >> project.. >>> >> >> >>> >> >> it shows the errors like primarykey field must be the Long >>> datatype.. >>> >> >> >>> >> >> can u please suggest me to create the database through appfuse .. >>> >> >> >>> >> >> >>> >> >> Sudhakar >>> >> >> >>> >> >> >>> >> >> >>> >> >> >>> >> >> -- >>> >> >> View this message in context: >>> >> >> >>> >> >>> http://www.nabble.com/Appfuse2-Struts-problem-tp20974893s2369p20974893.html >>> >> >> Sent from the AppFuse - User mailing list archive at Nabble.com. >>> >> >> >>> >> >> >>> >> >> >>> --------------------------------------------------------------------- >>> >> >> To unsubscribe, e-mail: [email protected] >>> >> >> For additional commands, e-mail: [email protected] >>> >> >> >>> >> >> >>> >> > >>> >> > --------------------------------------------------------------------- >>> >> > To unsubscribe, e-mail: [email protected] >>> >> > For additional commands, e-mail: [email protected] >>> >> > >>> >> > >>> >> > >>> >> >>> >> -- >>> >> View this message in context: >>> >> >>> http://www.nabble.com/Appfuse2-Struts-problem-tp20974893s2369p20988292.html >>> >> Sent from the AppFuse - User mailing list archive at Nabble.com. >>> >> >>> >> >>> >> --------------------------------------------------------------------- >>> >> To unsubscribe, e-mail: [email protected] >>> >> For additional commands, e-mail: [email protected] >>> >> >>> >> >>> > >>> > >>> > -- >>> > Atentamente >>> > Oscar Alvarez V >>> > (09) 8416 4052 >>> > >>> > >>> >>> -- >>> View this message in context: >>> http://www.nabble.com/Appfuse2-Struts-problem-tp20974893s2369p21008315.html >>> Sent from the AppFuse - User mailing list archive at Nabble.com. >>> >>> >>> --------------------------------------------------------------------- >>> To unsubscribe, e-mail: [email protected] >>> For additional commands, e-mail: [email protected] >>> >>> >> > --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
