<< Building an application which supports Plug-ins | Get Calling Method information >>

Using an ORM, Start with loading data

March 31, 2008 01:29 by Dave

Quick info

Very quick guide, ORM stands for Object Relational Mapper, its a tool which takes the data from a database and populates this data into Business Objects.. Nice and simple... basically using an ORM should save you as a coder from having to write the Data Access Layer code. (I'm not saying this is the best way to do things, that boils down to what you need to do.) For this code example i will be using WilsonORM there is a free download which will allow you to create a debug only project (other than that you have to pay a one off charge).

Back to the sample code.

1.Table

Lets start with the database, I will use one that came with this blog (a little change from northwind, I may do it with step 2).

CategoryId = GUID
CategoryName = Varchar(50)

I will only concentrate on this single table (keep it simple)

2. .Net Code

Now we will have to create a console application which will be extremely simple, it will contain the business object class for the above table, and a simple script which will list all the Categories in this table.

Create a new console project all this "TestOfORM"
Add a reference to the WilsonORMapper.dll (I'm using the .net 2 version, but the 1.1 will do)
Now add a BO sub folder in your project.

Now lets review what is required to get this to work:

Corresponding Business Object Class
Manager Class, basically is use to initiate the Object Space
Mapping File (contains meta data of how the table relates to the Business Object Class)
Actual Application code.

3. The Business Object Class

This class will be used to store the information for an instance of data in the table. Here is what my Class will look like

Things to note, you need a parameterless constructor, also there is s field which will relate to the columns in the table.

4. Manager Class

This will create an instance of the ORM manger (object Space), this will be used in your app code to load data from the database.

using System;
using Wilson.ORMapper;

namespace TestOfORM
{
sealed public class Manager
{
private static ObjectSpace engine;

  public static ObjectSpace Engine {
   get { return Manager.engine; }
  }

  static Manager() {
   string mappingFile = AppDomain.CurrentDomain.BaseDirectory
                + "Mappings.xml";
   string connectString = @"Server=.\sqlexpress;DataBase=theBlogDB;UID=user;PWD=passsword;";
   string providerType = "MsSql";

   Provider provider;
   try { provider = (Provider) System.Enum.Parse(typeof(Provider), providerType, true); }
   catch { provider = Provider.MsSql; }

   // Note: Non-Zero Session may be desirable for Server Applications
   engine = new ObjectSpace(mappingFile, connectString, provider);
  }

  private Manager() {
   // Note: Static Class -- All Members are Static
  }
}
}

this code i just copied off Wilson's site, and changed the mappingFile and connectionString varibles.. now you are almost there.

5. Mapping file

This file will contain all the entity mappings, the easiest way to build this file is to copy one off a sample which comes with the OEM and change it to your requirements. One cool thing is Paul Wilson included the .XSD file, so you can set this to validate your shema.

<?xml version="1.0" encoding="utf-8" ?>
<mappings version="4.2">
<entity type ="TestOfORM.BO.be_Categories" table ="be_Categories" keyMember ="_CategoryID" keyType="Auto">
<attribute field ="CategoryID" member ="_CategoryID" alias ="CategoryID" />
<attribute field ="CategoryName" member ="_CategoryName" alias ="CategoryName"/>
</entity>
</mappings>

as you can see there is only 1 entity, with 2 attributes.. this is mapping the be_Categories table to the be_Categories class, things to notes:

keyType - is how the Primary key is generated
KeyMember - is the tables primary key

6. Your App Code

finally you can code your app, it may seem like a lot of work, but the larger the project the more likely you would find this faster to code, plus some of the you can generate using tools

class Program
{
    static void Main(string[] args)
    {
        ObjectSet allCat = Manager.Engine.GetObjectSet(typeof (be_Categories), string.Empty);

        foreach (object o in allCat)
        {
            be_Categories cat = (be_Categories) o;
            Console.WriteLine(cat.CategoryName );
        }
        Console.ReadLine();
    }
}

as you can see I call the managers get all of that type, which returns an ObjectSet, then i just list all the entries. Nice and simple. The following screen shot shows the final layout of my project: