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reflection of database data to an object

Posted on 2003-11-20
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Last Modified: 2010-04-16
I was wondering if anyone knew if there was a way to instantiate an object and then that object use reflection on itself. i.e.

I instantiate an object by calling it like this.

Employee e = new Employee("someID");

then in the process of creating itself employee calls some reflection method to instantiate it's own properties.

Anyone seen this happen?  I've got an idea of how it should be done but just having a hard time figuring it all out.

I am using this article as a basis:

http://www.c-sharpcorner.com/Code/2002/April/ReflectingDataXMLTL004.asp
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Question by:jayrod
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purpleblob earned 500 total points
ID: 9788900
Yes this is be possible below is an example (if this is indeed what you want to do) obviously it seems a little odd using reflection in this manner as when you write the object you'll obviously know the properties etc. , so I assume you've got some clever reason for using reflection for such a process :-)

Anyway, this will work

public class Employee
{
   private int m_Value = 0;

   public int Val
   {
      get { return m_Value; }
      set { m_Value = value; }
   }
   public MyObject(string something)
   {
      Type t = this.GetType();
      PropertyInfo[] pinfo = t.GetProperties();
      t.InvokeMember(pinfo[0].Name, BindingFlags.SetProperty, null, this, new object[]{123});
   }
}

Now if you call this from somewhere else, i.e.

Exmployee obj = new Employee("someID");
int i = obj.Val;

This will assign i the value 123 which was set via reflection within the constructor.

Hope this helps
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Expert Comment

by:purpleblob
ID: 9788922
Whoops, sorry as I was changing the code to reflect your Employee object I forgot to alter the constructor from MyObject to Employee.
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Author Comment

by:jayrod
ID: 9789215
The clever reason is that the properties represent field names in a database. It seems that in order to do this before I would tell the object to get the row corresponding to the object from the database and then manually set each property.  Now this works fine.. but if I changed the database table at all I had to change the code.

I was hoping to find a way to do this dynamically. I asked about this topic a few months back(before I knew anything about reflection) and I eneded up using Hashtables and ArrayLists to represent my data. But this has become way too obscure.

thank you for this code. I'm going to test it out right now :)
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Author Comment

by:jayrod
ID: 9789582
Outstanding!!!!!

Here is the final code. This is a method that will instantiate it's own properties (mind you the properties need to have a Set parameter) with a row from the database.

string sqlString = "select * from nrlfcuDepartments where departmentID = @departmentID";
r1 = SqlHelper.ExecuteReader(connection, CommandType.Text, sqlString, new SqlParameter("@departmentID", this._departmentID));

r1.Read();
if(r1.HasRows)
{

      Type t = this.GetType();
      PropertyInfo[] pinfo = t.GetProperties();

      for(int i=0;i<r1.FieldCount;i++)
      {
            try
            {
                  string name = r1.GetName(i);
                  t.InvokeMember(
                        r1.GetName(i),
                        BindingFlags.Default | BindingFlags.SetProperty,
                        null,
                        this,
                        new object [] { r1.GetValue(i) }
                        );
            }
            catch
            {//Means that a value was null or a fieldName has been changed                                    
            }
      }
}
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Expert Comment

by:purpleblob
ID: 9789721
Ah, I suspected it might have something to do with initiating your object from a database record :-)

I did see something rather cool on codeproject which used Attributes to say which properties should be set from the database, I think it was this on http://www.codeproject.com/cs/database/dal1.asp I only had a glancing look but you might find it useful/interesting
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