the list of genders (or whatever look up) should be separate from the
actual entity. validation can be done any number of ways. attributes,
Validator<T>, or a series of simple bool returning members on the
entity itself. I would treat Gender as a value object/entity using NH
mappings instead of a string. this would allow for strategies of
gender specific functionality. instead of logic like
if(person.gender == "M"
{
}
else if(person.gender == "F")
{
}
you could do
person.gender.dosomething();
i would probably go with a combination of validation attributes
(castle validation component) and IValidator<T> where the validation
logic can be placed in a central location. The systems I design are
small so I find this works well for me.
On Feb 9, 7:04 pm, Dathan <[email protected]> wrote:
> Something like
> PersonTbl (PersonId INTEGER PRIMARY KEY IDENTITY(1,1), Name NVARCHAR
> (255), GenderId INTEGER REFERENCES GenderTbl(GenderId));
> GenderTbl (GenderId INTEGER PRIMARY KEY IDENTITY(1,1), Gender NVARCHAR
> (10));
>
> But where Person.Gender is a string, and is at some point by the DAL
> resolved into the GenderId that corresponds to the value of the Gender
> column with the same string value.
>
> The contents of GenderTbl should never be changed by the DAL (I don't
> want users defining new genders!), but we do have a case where users
> being able to add to such a list might be necessary (e.g., it might be
> necessary to allow users to add new cities to our gazeteer). So,
> since I'm a newbie to the terminology, yes, you might say the Gender
> list is persistent, but I'm not trying to persist a collection of
> genders per person. Just a single Gender per person, plus supporting
> some mechanism for validating that what the user has selected in the
> frontend is a valid gender.
>
> But I guess even that's not quite right... I don't want to persist a
> Gender object per Person (a one-to-one relationship). I want to
> create a many-to-one relationship where each Person has a reference to
> either the, e.g., "Male", "Female", or "Unknown" gender. But I'd like
> to be able to, somewhere (and it just makes sense to me to do it as
> part of the object model, rather than externally in the UI logic), get
> a list of all valid genders (currently I do this as a string -- would
> it make more sense to create a Gender object for this?) for use both
> in validating user input (is the user's input in the set of valid
> genders?), and in UI presentation.
>
> On Feb 9, 4:39 pm, Fabio Maulo <[email protected]> wrote:
>
> > The "Gender" list is persistent ?
>
> > 2009/2/9 Dathan <[email protected]>
>
> > > Thanks for the reply!
>
> > > The list is, as you surmise, for UI drop-down population, but also for
> > > run-time validation. I'd rather validate the value of the Gender
> > > property immediately (via either Dictionary.ContainsKey() or List.Find
> > > (), as you suggest) than waiting for NHibernate to throw an error when
> > > I try to serialize the entity back to the data store (I'm an NH
> > > newbie, so please correct me if I'm wrong about the behavior in this
> > > regard). I'm open to advice on best practices, though, if this is the
> > > wrong way to go about it.
>
> > > Given that a list of valid genders is also of use in data validation
> > > (which seems to be very much a domain concern, rather than strictly a
> > > UI concern), not just UI control, it seems logical to me that embedded
> > > in the person entity is an appropriate place for this information. I
> > > take it this is contrary to DDD / MVC / other best practices?
>
> > > ~Dathan
>
> > > On Feb 9, 3:33 pm, Jason Meckley <[email protected]> wrote:
> > > > why does the person entity have a static list of genders? if it's just
> > > > for UI dropdown list selection, this can, and should, be done outside
> > > > to scope of the person entity.
> > > > I would also recommend using 2nd level cache for memory storage of the
> > > > gender list rather than a static list. and I would recommend waiting
> > > > on implementing the cache until
> > > > 1. preformance is a documented and measurable issue
> > > > 2. the problem is loading the genders and not another issue (select n
> > > > +1 or unrestricted list results).
>
> > > > the person entity would just have a Gender property which you would
> > > > get;set; to a Gender field. no need for a dictionary of genders within
> > > > the person entity. also, if you are going to keep a collection on any
> > > > entity. use IList<T>, in this case IList<Gender>. key, value
> > > > containers do not express intent and the same functionality can be
> > > > gained using list.Find(predicate).
>
> > > > On Feb 9, 12:45 pm, Dathan <[email protected]> wrote:
>
> > > > > I'm considering porting my existing DAL to NHibernate instead. But
> > > > > I've been reading the documentation, and there's one feature of the
> > > > > way my object model currently works that I haven't figured out an
> > > > > elegant way to do using NHibernate yet.
>
> > > > > Say I'm representing a person. That person has a Gender property. In
> > > > > the database, that gender property is a foreign key to
> > > > > GenderTbl.GenderId, and GenderTbl.Gender holds the string that
> > > > > describes the person's gender. What I'm doing currently is having
> > > > > something like the following:
>
> > > > > public class Person
> > > > > {
> > > > > private string gender;
> > > > > private static Dictionary<string, int> genderDict;
> > > > > private static IList<string> genderList;
> > > > > .
> > > > > .
> > > > > .
> > > > > public string Gender
> > > > > {
> > > > > get
> > > > > {
> > > > > return gender;
> > > > > }
> > > > > set
> > > > > {
> > > > > if (!genderDict.ContainsKey(value))
> > > > > throw new ArgumentException("Invalid gender");
> > > > > gender = value;
> > > > > }
> > > > > }
>
> > > > > public IList<string> GenderList
> > > > > {
> > > > > get
> > > > > {
> > > > > return genderList;
> > > > > }
> > > > > }
>
> > > > > }
>
> > > > > My DAL initializes Person.genderDict and Person.genderList to reflect
> > > > > the contents of GenderTbl -- genderDict is used to lookup the primary
> > > > > key of a gender when the Person is serialized back to the database
> > > > > (there's a UNIQUE constraint on GenderTbl.Gender, so this reverse
> > > > > lookup will be valid). I could just as easily do something like:
> > > > > private int gender;
> > > > > private Dictionary<int, string> genderForwardDict;
> > > > > private Dictionary<string, int> genderReverseDict;
> > > > > public string Gender
> > > > > {
> > > > > get{ return genderDict[gender];};
> > > > > set{ if (!genderReverseDict.ContainsKey(value)) throw new
> > > > > ArgumentException(); else gender = genderReverseDict[value];}
>
> > > > > }
>
> > > > > And I'd be fine with that. What I haven't figured out is how to get
> > > > > NHibernate to populate a static list of the legal values for the
> > > > > gender field (genderDict). Or is there some other way to do this that
> > > > > I'm missing? Specifically, I do this so view-related controls can
> > > > > bind to the list of legal values so the user can select from a combo
> > > > > box rather than having to perform a search every time or type in a
> > > > > string, etc.
>
> > > > > Thanks!
>
> > > > > ~Dathan
>
> > --
> > Fabio Maulo
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