Re: DataSet's Vs Object Model

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From: David Jessee (djessee_at_houston.rr.com)
Date: 11/26/04 

Date: Fri, 26 Nov 2004 08:28:26 -0600

If you have a class that implements IComparer that has properties you can
set, or a constructor:

e.g. new MyCoparer(new object() {"FirstName","ASC","LastName","DESC"})

you could make the implementation of the class use reflection to determine
which properties to compare (FirstName, LastName) and how to order them
(ASC, DESC)

"MattC" <m@m.com> wrote in message
news:Or1cOr50EHA.2292@TK2MSFTNGP15.phx.gbl...
> Thanks guys,
>
> Yeah so far I have been implementing an object model driven design where
> possible using Collection classes specific for the obejcts and yeah those
> sealed IComparer classes are cool.
>
> On that Topic is there an interface that will allow yoo to create a filter
> for a collection.
>
> Failing that, I guess I will have to implement filtering support in the
base
> collection class and try to make it overidable, a la Sort.
>
> MattC
>
> "David Jessee" <djessee@houston.rr.com> wrote in message
> news:O5m39420EHA.1260@TK2MSFTNGP12.phx.gbl...
> > First, on the fact of sorting, look at the IComparer Interface. I know
> > that's not what the message was really about, but its a good piece of
> trivia
> > :-)
> >
> > Making a migration from a data-centric approach to development to an
> > object-centric approach is difficult. Especially when you're talking
> about
> > object persistence in a relational database. I've had to do all sorts
of
> > things to facilitate the process (e.g. having constructors that take an
> > IDataReader, Having collections implement a "ParentId" Method).
> >
> > I can tell you the things that have helped me a lot, though.
> > First, only look at the persistence model after you have flushed out
your
> > object model. Create Factory classes that manage Instatiation and
> > Repository Classes that save Instances and perform lookups. But ONLY
look
> > at the external interfaces for these ... don't think about what the
tables
> > will look like because sometimes after you have a good understanding of
> your
> > model, certian aspects of your model will behave best if they're (dare I
> say
> > it) de-normalized. Sometimes the relational view of your persistence
will
> > not have a 1-to-1 correlation with your classes (there's a belief that
if
> > there's a person class, there should also be a person table).
> >
> > Once your model has been flushed out, and you understand its behavior,
you
> > can start looking at a relational model for it. note, you may have to
> make
> > some adjustments in your model to accomidate for the relational
> integration.
> >
> > There are a number of tools out there that accomplish this task.
> > Additionally, there are some persistence frameworks in development on
some
> > public sites (do a search for "persistence" on gotdotnet.com). But
> > ultimately it comes down to you finding the best way for your model to
be
> > persisted. For instance, I have one project in the works with a rather
> > complex object has to be saved to the database. Since this complex
> > hierarchy (7 type definitions and 4 collection types) will not need to
be
> > queried, I'm serializing the entire instance to a memory stream, base64
> > encoding the result and sticking it into a text field.
> >
> > One book I read that gave me a lot of insight into this process was
> > "Domain-Driven Design: Tackling Complexity in the Heart of Software"
(Rick
> > Evans). You'd definately get something out of it.
> >
> >
> >
> > "MattC" <m@m.com> wrote in message
> > news:Oy3CgUt0EHA.1260@TK2MSFTNGP12.phx.gbl...
> > > Hi,
> > >
> > > I have question that I'd like to throw up for a discussion as I cant
> seem
> > to
> > > figure out the answer myself.
> > >
> > > I have implemented an object model in an ASP.NET application. Classes
> use
> > > inheritance, aggregation and all the other OO means of data
> encapsulation.
> > > The persistant store for the data is a database, so 3rd Normal form
> etc...
> > >
> > > Here's where thing get interesting (well, kinda). I have create a
> series
> > of
> > > collection classes that derive from ArrayList and allow objects within
> my
> > > objectmodel to be stored in their respective collection class. For
> > example
> > > a Department class with have a related DepartmentCollection class for
> > > storage of many objects.
> > >
> > > These collections can then be bound to a datagrid and using the bound
> > column
> > > template I can pick any data from the object model, so I can display
in
> > the
> > > grid the salary of the manager of each department in the collection.
> > >
> > > This is great and very flexible. However, if I wish to use the
features
> > > provided by ADO.NET then having an object model is not so useful. For
> > > example a user table exists of the username, securityprofileid and
> > > activeaccountflag, departmentID. Pulling out the user details into my
> > user
> > > class would then fill all the details relating to the class, so the
> > > Department ID is used to get the aggregate Department object and the
> same
> > > with the SecurityProfile object. With a DataTable I would only have
> that
> > > data which came from the table, i.e, the four fields with the object
> model
> > > much more data.
> > >
> > > So when I come to use sorting or filtering which is provided by the
> > > DataTable class I can only sort and filter on those fields available.
> If
> > I
> > > want the same data as in my previous example of the manager's salary,
I
> > > would need to create a DataSet that contained then data I wanted to
> > display
> > > in that grid. Somewhat bypassing the object model.
> > >
> > > I would love to read any thoughts people have or suggestions, I am by
no
> > > means an expert onteh subject so it is entirely possible that I have
> > missed
> > > something very simple.
> > >
> > > TIA
> > >
> > > MattC
> > >
> > >
> >
> >
>
>

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