c# data object model representation

Question

I am learning c# at the moment, I used to program using Unix/C - Oracle and lately I am learning to do windows programming.

Since in c# (or at least using MVC) the data or database table is represented as object/class.

For example say, a simple computer shop part tracking; a shop can purchase a computer and dismantle it into parts and they can sell the parts; or the parts can also be purchase from supplier individually. in relational database we can have something like

Table: Computers
Fields: ComputerId, Maker, PONumber, SerialNumber, DismantleFlag

Table: Parts
Fields: PartId, ComputerId, PONumber, PartDescription, SerialNumber

say if the shop want to trace a part where they but it from, we do query on parts table using part serial number if computerId is null then get the detail where the part is bought from using PONumber, if computerId is not null then use PONumber from computers table.

so if we do the same using model representation I think it would go something like this. (I know the syntax is not correct, it's just a representation)

class Part
{
   properties PartId, PONumber, PartDescription, SerialNumber
}

class Computer
{
   properties ComputerId, Maker, PONumber, SerialNumber, DismantleFlag

   List<Part>Parts
}

so I would assume there will be object for a list of Parts to store all the parts that purchase individually and there is also object for a list computers which in turn has a list of parts inside them if DismantleFlag is Y.

is that mean if I want to do the same operation to trace the parts, I have to go trough the list of parts object, and I also need to go through list of computers object and for each computer object I need to scan through all the parts with in the computer object?

if my understanding is correct then relational database is more simpler to store and manage data, and how it is going to be translated in MVC if the data/model is not represented in object form?

Thank you.

Answer 1

I am assuming the following rules are possible in your scenario:

1. Computers have Parts
2. Parts might or might not be contained in a computer
3. Parts can migrate from one computer to another
4. you might want to keep a history of part migration.

Computers and Parts would be completely independent entities. Relationship between Computers and Parts would be Many to Many.

This is the basic model structure I would create given the rules above.

The Boolean Current in the ComputerParts table would represent wether the relation ship is the current one (true if part in this computer or false if part no longer resides in this computer) this approach allows for almost any Computer vs Parts relationships imaginable.

These classes are the most basic of models and would perhaps be modified if you where using an ORM like Entity Framework. Hope this helps

public class Computers
{
    public string ComputerID { get; set;}
    public string Maker { get; set;}
    public string PONumber { get; set; }
    public string SerialNumber { get; set; }
    public Boolean DimantleFlag { get; set; }
    public DateTime DateCreated { get; set; }
}

public class Parts
{   
    public string PartID { get; set; }
    public string PONumber { get; set; }
    public string SerialNumber { get; set; }
    public string PartDescription { get; set; }
    public DateTime DateCreated { get; set; }
}

public class ComputerParts
{
    public string ComputerID { get; set; }
    public string PartID { get; set; }
    public Boolean Current { get; set; }
    public DateTime DateCreated { get; set; }
}

Answer 2

Often in asp.net-mvc your data actually is stored in a relational database, and you use a framework like Entity Framework to translate the results of sql queries into your model representation.

Entity Framework also supports LINQ, which uses a more Sql-like syntax. So if you're using EF, a similar query might look like this.

// in practice, we might put this in a using statement
var db = new MyDbContext();

var qry = 
    from p in db.Parts
    join c in db.Computers on p.ComputerId equals c.ComputerId
    where p.SerialNumber == mySerialNumber
    select c.PoNumber

string poNumber = qry.FirstOrDefault();

Now, the query you actually seem to want will probably might use a left-join. The left-join syntax in linq is a little funky, but it's at least usable

var qry = 
    from part in db.Parts
    join ljcomp in db.Computers on part.ComputerId equals ljcomp.ComputerId into gcomp
        from comp in gcomp.DefaultIfEmpty()
    where part.SerialNumber == mySerialNumber
    select comp == null ? part.PoNumber : comp.PoNumber

Behind the scenes, EF translates your linq query into sql, and executes it against the database, and then can convert it into your string value, or even into an object if that's what you tell it to select.

---

You don't have to use Entity Framework, you can communicate with the database in other ways, but for now I'll leave that research as an exercise to you.

Answer 3

In Model-View-Controller(MVC). There's is different ways of Creating Your Models (Which is the Class You want to create to store your data).There are Code First And Entity framework database first approach

This is a Code first approach example http://tutlane.com/tutorial/aspnet-mvc/code-first-approach-in-entity-framework-in-asp-net-mvc-with-example

This is an Entity framework database first approach example http://www.c-sharpcorner.com/UploadFile/8ef97c/mvc-5-0-application-using-entity-framework-db-first-approach/

Hope this helps