C# Discussion Boards - CodeProject

behrang Javaaherian11-Dec-02 22:55

11-Dec-02 22:55

Suppose you want to write an Adress Directory Application. In Object Oriented environment you have a Class called Party. All the information that both companies and persons have goes here. and you have to class Person and Company derived from party that have their own information. in Database you can have two diferrent aproaches:
1. you have a Party table which have all the field that person and company requires then when you have a person , fields which are for company are set to null.
2. you have a Party table contains only common field and another Person and Company tables for storing type dependent information on them ( a one to one relation between party and these two table also required)
in any of these aproaches the object model are the same but the senario in database completely differs and this will influence the code.
OR mapping means mapping between objects in memory and persistence places ( like Relational Database System). We have a object graph in memory and we want to map this object graph into Database and vice versa we have a some database row and want to create Object graph from it!
a good OR mapping completely seperate the Persistecy of objects from the business logics.
Suppose the example agian. if we have a good OR Mapping framework we can simple write the code bellow :
Company comp = Company.getCompany();
comp.Name = "Microsoft";
Person pers = Person.getPerson();
pers.Name = "Bill";
pers.Family = "Gates";
pers.Company = comp;
PersistentLayer.AddForSave(pers);
PersistentLayer.AddForSave(comp);
PersistentLayer.Save();
so the code is not filled with any SELECT or other Sql Commands. All the Sql commands are in one place and PersitentLayer Engine use some logic to create them.
I hope it was useful for you.
Regards
Behrang

Re: .NET Framework OR Mapping

leppie12-Dec-02 8:06

leppie

12-Dec-02 8:06

So it acts as a persisted wrapper class? eg

public class Company {
  public static Company GetCompany()
  {
    do_sql_insert_with_defaults_here();
    return retrieve_newly_created_record();
  }
  ...
  public string Name 
  {
    get {return name;}
    set {name = value; Update_record_in_sql();}
  }
}

I'm not sure if I have the idea right here...? But it does sound like a good concept. I try to have a look at OPF, but no source is available... Frown | :(

Cheers

WebBoxes - Yet another collapsable control, but it relies on a "graphics server" for dynamic pretty rounded corners, cool arrows and unlimited font support.

Re: .NET Framework OR Mapping

behrang Javaaherian13-Dec-02 19:07

behrang Javaaherian

13-Dec-02 19:07

Hi leppie,
This is the way that most of the developers do now. this means having some functions in each class for loading from database. but in this the SQL Commands is in all codes and also we have lots of redundant code in each class. Also another problem is with relations. For example a Person may have a property Called Comapany which point to the company which it works! in this way it is hard to figure out this issue. Another problem is that an object may have lots of property which each have Different Persistent places. For example in our current project we are developing an orderprocessing program. The Adress Directory is currently in Lutos notes. so for example we have a Person object the name , family , email adress, etc are comes from LDAP Server in lutos notes. other business dependent properties like Roles which it accepts are come from RDMS.
An OR Mapping Tool use some Descriptor files ( mostly in XML format for describe an object).
Regards
Behrang

Re: .NET Framework OR Mapping

leppie13-Dec-02 23:32

leppie

13-Dec-02 23:32

Thanks, although it sounds nice, its way above my fireplace Smile | :)

behrang Javaaherian wrote:
For example a Person may have a property Called Comapany which point to the company which it works! in this way it is hard to figure out this issue. Another problem is that an object may have lots of property which each have Different Persistent places.

I was wondering about how you would "tackle" such a situation...especially coming from different sources.

WebBoxes - Yet another collapsable control, but it relies on a "graphics server" for dynamic pretty rounded corners, cool arrows and unlimited font support.

Re: .NET Framework OR Mapping

behrang Javaaherian13-Dec-02 23:56

behrang Javaaherian

13-Dec-02 23:56

For tackle into problem which should delegates all the reffrences into our engine to load from Database. suppose a Person object again it has some properties : (name , family, etc). The key feature here is to capture access to name property and delegate ( means route and have nothing with delegates in C#) into our engine. this is possible in languages like Objective-C ( it is another great programming language from Apple). in C# we should use another way. The way that I used it using Keypath Access instead of Property. means that for example for access name of a person i use person["Name"] instead of person.Name. In this way all the access goes through an indexer function. the indexer function parse the string and find appropiate operation from Descriptor files. if I want to use properties either i should write My own wrapper functions like this

string Name
{
get {return this["Name"];}
set {this["Name"] = value;}
}

I wrote a simple OR Mapping tools in C# but the code is not clean enuogh to understood and it needs refactoring. if anyone wants the code please send an email to me for code. Smile | :)

Regards
Behrang

Re: .NET Framework OR Mapping

leppie14-Dec-02 0:17

leppie

14-Dec-02 0:17

behrang Javaaherian wrote:
The way that I used it using Keypath Access instead of Property.

So access to the object is via it PK(or Unique Key) iow SELECT * FROM MyType WHERE col = value. The return set then becomes the object?

behrang Javaaherian wrote:
I wrote a simple OR Mapping tools in C# but the code is not clean enuogh to understood and it needs refactoring. if anyone wants the code please send an email to me for code.

I would be interested, to see what you mean a bit more clearly. I find code easier to understand Smile | :)

WebBoxes - Yet another collapsable control, but it relies on a "graphics server" for dynamic pretty rounded corners, cool arrows and unlimited font support.

Re: .NET Framework OR Mapping

behrang Javaaherian14-Dec-02 1:02

behrang Javaaherian

14-Dec-02 1:02

The Idea i used in my code is like the idea which the EO developer team done in Enterprise Objects. I assumed each table in database have CLASS column. in this class I hold the class of the object which should be instansiated. all the objects are derived from a base class Called Entity. The Entity class is the core class for my framework. I get Entity Objects from another SingleTone class called EntityManager. The code would be like this:
Entity en = EntityManager.getEntity("Party",new EntityKey(123));
this means loading entity which the parent of it is Partey and the primary key is 123 .
The EntityKey is another object. I used this object to be able to have none-numeric primary keys.
The FrameWork First Load the XML File which describe the Party. (Party.XML for example) this Descriptor shows the Primarykey field and also Table name of the Party ( For exmaple pk , Party)
then a Query command for getting the class the sql command is : "SELECT CLASS FROM PARTY WHERE pk=123".
The Query will return For example PERS. the program will create the appropiate class name (Forexample Model.Person) this class should be inherited from Entity. now the Framework loads the person.Xml , find the properties from descriptor and create appropiate SQL Command for loading other information of the Person. The Simple attribute have no problem. The problem is with relations. Suppose a Person have a relation to another Object in another table. The Framework can work in to different way :
Load it when the Parent Object loaded ( Early)
Load when access to it required (Lazy)
the lazy loading is done through proxy objects ( refer to design pattern book to see what is Proxy Object).
Regards
Behrang Smile | :)

Re: .NET Framework OR Mapping

leppie14-Dec-02 1:14

leppie

14-Dec-02 1:14

Thanx for the info. It all sounds tooo complicated for my liking. I wouldn't mind seeing it in action though Smile | :)

behrang Javaaherian wrote:
I assumed each table in database have CLASS column. in this class I hold the class of the object which should be instansiated.

Arrgg, I hate assumptions! So the derived class needs to get serialized into the class column? Come one just send the code Smile | :)

WebBoxes - Yet another collapsable control, but it relies on a "graphics server" for dynamic pretty rounded corners, cool arrows and unlimited font support.

Re: .NET Framework OR Mapping

leppie14-Dec-02 1:29

leppie

14-Dec-02 1:29

Another question.

Is the objects based on a existing DB or does the DB get "created" according to the class?

[edit] iow is DB modelled according to .NET object or is the .NET object modelled on a DB object?[/edit]

WebBoxes - Yet another collapsable control, but it relies on a "graphics server" for dynamic pretty rounded corners, cool arrows and unlimited font support.

Re: .NET Framework OR Mapping

behrang Javaaherian14-Dec-02 1:33

behrang Javaaherian

14-Dec-02 1:33

It is a very good fantastic the Framework would be able to create DDL ( SQL Command for creating tables) file for xml descriptors but the framework is not able to do it.
Regards
Behrang

Re: .NET Framework OR Mapping

MikeDoerfler12-Dec-02 2:42

MikeDoerfler

12-Dec-02 2:42

I have been doing some looking into OR solutions(open/free & commercial) and found an open source project that is still in the planning stages that looks very promising. So you might want to take a look at it instead of starting another project. From reading some of the discussions it looks like they are going to build something similare to Hibernate.

http://opf.sourceforge.net/[^]

If anybody would like I can post a list of OR mappers for .NET that I have found.

Mike

Re: .NET Framework OR Mapping

behrang Javaaherian12-Dec-02 3:57

behrang Javaaherian

12-Dec-02 3:57

thanx Mike,
I have downloaded the opf before. The opf is not design well. Also it has nothing for support Distribution. I worked with lots of OR Mapping tools. The best tool is Cocobase ( $6000 Per developer , Per project !!!!) and the Entriprise Objects (EO)(Part of Web Objects from Apple ) is very good product. so I prefer the same Approach as apple developer's team done in EO.
Regards
Behrang

Re: .NET Framework OR Mapping

MikeDoerfler12-Dec-02 4:33

MikeDoerfler

12-Dec-02 4:33

Behrang, I am curious about what parts of the design you don't like. I always appreciate others opinions/thoughts on products. I haven't looked at EO, but will do so ...

Thanks for the info!

Mike

launching file search window programmatically

Anonymous11-Dec-02 17:44

Anonymous

11-Dec-02 17:44

Hello

Anybody know how I would programmatically launch a "file search window" from an application being developed in .net (C# or visual basic). Basically what I want is to be able to click on a button on my application and have a similar result as if I clicked on the "Search->For Files or Folders..." menu item of the windows start menu.

Thanks for any help you can provide.

Re: launching file search window programmatically

Kannan Kalyanaraman11-Dec-02 18:45

Kannan Kalyanaraman

11-Dec-02 18:45

Have a look at IShellDispatch set of interfaces.
It has scriptable(IDispatch) methods which you can call from languages like vb6.
From .net you need to add reference to shell32.dll which will be in the system32 folder and this is the code to call the search for files dialog.

<br />
ShellClass obj = new ShellClass();<br />
obj.FindFiles();	<br />

Hope this helps.

Cheers
Kannan Smile | :)

Re: launching file search window programmatically

AJ7012-Dec-02 9:16

AJ70

12-Dec-02 9:16

Thanks a bunch Kannan,

Thats exactly what I wanted, it was almost too easy Big Grin | :-D

Resources- I'm lost!

peterchen11-Dec-02 12:29

peterchen

11-Dec-02 12:29

How do resources work in .NET?
I'm just trying to include a bitmap for an imagelist...

However, MSDN talk either about ".rc" files which somehow I cannot add to my project (or can I?), or about .resx files being "the .NET" way and their cute and politically correct features how to localize your dialog resources and web apps (something I promise to look into once I get those friggin' folder icons into my tree view!)

Is there a Tutorial in MSDN? An article on CP? A merciful soul that gives me some step-by-step-instructions?

Oh, when we're at it... :blush: ...how do I get the "hinstance" i need for Bitmap.FromResource? or can I pass "null" for "me"?

Thanks

If I could find a souvenir / just to prove the world was here [sighist]

Re: Resources- I'm lost!

Nick Parker11-Dec-02 16:54

Nick Parker

11-Dec-02 16:54

peterchen wrote:
An article on CP? A merciful soul that gives me some step-by-step-instructions?

Yes, JTJ has written a nice article on embedded resources in .NET. Understanding Embedded Resources in Visual Studio .NET[^]

Nick Parker

Not everything that can be counted counts, and not everything that counts can be counted. - Albert Einstein

C# ActiveX

11-Dec-02 10:47

Hi all

I want to create an ActiveX Control using c# and import it in non .NET application (MFC 6). How can it be done (I dont want a simple class, but visual control)? Generaly, what is the approach of .Net toward ActiveX, can I stil create an ocx file and use it in MFC(6) app?
If Activex is not relevant any more, how can use a .Net (c#) control from MFC app?

It would be greate if u could direct me to some data source about this...

thanks Smile | :)

Re: C# ActiveX

Adrian Hall17-Dec-02 15:09

Adrian Hall

17-Dec-02 15:09

I'm a beginner in .NET so take this all with a grain of salt.

An ActiveX control is basically a COM object that produces windows output.

Ergo, you need to construct a COM object in reality - maybe perhaps a COM object that is also a Control.

I noticed in the Articles section there are a couple of articles on COM Interop and creating COM objects out of .NET objects.

-Adrian

SDLDMO and a Detached

Paul Watson11-Dec-02 9:36

Paul Watson

11-Dec-02 9:36

I have the following code which returns a Columns array back to the caller. The code is C# (no really!) with COM interop on the SQLDMO COM object.

SQLDMO._SQLServer sqlserverMain = new SQLDMO.SQLServerClass();
sqlserverMain.Connect(this.ServerName, this.UserName, this.Password);
SQLDMO.Database sqldatabaseCurrent = (SQLDMO.Database)sqlserverMain.Databases.Item
    (this.Database, sqlserverMain);							
SQLDMO.Table sqltblCurrent = (SQLDMO.Table)sqldatabaseCurrent.Tables.Item
    (this.Table,sqlserverMain);
return sqltblCurrent.Columns;

So it creates a SQLDMO server connection, then gets a database, then gets a table and finally gets all the Columns for that table and returns that array.

However there is no sqlserverMain.DisConnect(); because of my problem. Basically if I put in the disconnect code then when I want to use the returned Columns array I get a "This object has been detached from SQLDMO, as the result of a refresh, automatic shutdown, error or App.Quit" error message.

If if leave out the disconnect then it all works fine.

Now my guess is that this is a classic reference vs. value problem with the return array. I am returning a reference rather than the value.

This is probably really, really simple but then how do I return the value and not the reference? I need to disconnect because otherwise I am leaving the connection open and by watching Taskmanager I noticed the app just kept eating memory without releasing every time that specific method was called. With the disconnect (but avoiding the error) the app eats memory and then releases it on disconnect.

ta

Paul Watson
Bluegrass
Cape Town, South Africa

NOPcode wrote:
...but in America, you're not allowed to thrust, moan or see anything...

Re: SDLDMO and a Detached

Nick Parker11-Dec-02 9:55

Nick Parker

11-Dec-02 9:55

Paul Watson wrote:
This is probably really, really simple but then how do I return the value and not the reference?

I am not sure if this will work Paul, but it is worth a shot. Could you return you value as an out parameter? What is the problem with reconnecting to the DB?

Nick Parker

Not everything that can be counted counts, and not everything that counts can be counted. - Albert Einstein

Re: SDLDMO and a Detached

Paul Watson11-Dec-02 10:08

Paul Watson

11-Dec-02 10:08

Nick Parker wrote:
I am not sure if this will work Paul, but it is worth a shot. Could you return you value as an out parameter?

Good idea, will give that a bash, thanks.

Nick Parker wrote:
What is the problem with reconnecting to the DB?

The code that returns the Columns array is in a SQLDMO helper class I made. I could leave the connection open but then I would have to make sure the caller remembers to close the connection, not very elegant or helpful at all. Also the caller may only act on the returned Columns array many minutes later, in which case I don't want that SQLDMO server connection sitting open all the time.

The good old Open Late, Release Early idea Smile | :)

Paul Watson
Bluegrass
Cape Town, South Africa

NOPcode wrote:
...but in America, you're not allowed to thrust, moan or see anything...

Re: SDLDMO and a Detached

Nick Parker11-Dec-02 16:20

Nick Parker

11-Dec-02 16:20

Paul Watson wrote:
The code that returns the Columns array is in a SQLDMO helper class I made. I could leave the connection open but then I would have to make sure the caller remembers to close the connection, not very elegant or helpful at all.

True, so why don't you just close the connection once you have receive the data in a dataset, since you said your not sure when the caller will work with the returning dataset and you have already written a helper class why not just do the clean up inside the function and close the connection.

***
If nothing I wrote above made any sense, don't blame yourself. I have had my head stuck in writing a binary tree for the last two hours, yuck. Dead | X|

Nick Parker

Not everything that can be counted counts, and not everything that counts can be counted. - Albert Einstein

Re: SDLDMO and a Detached

Paul Watson11-Dec-02 20:17

Paul Watson

11-Dec-02 20:17

Nick Parker wrote:
True, so why don't you just close the connection once you have receive the data in a dataset, since you said your not sure when the caller will work with the returning dataset and you have already written a helper class why not just do the clean up inside the function and close the connection

LOL no wonder I was getting confused. I was not thinking of using the DataSet (or any ADO.NET) at all. I was hopping the SQLDMO Columns collection could work disconnected, but alas no.

I am going to go the DataSet route now thanks to your and .S.Rod.s advice Smile | :)

Paul Watson
Bluegrass
Cape Town, South Africa

NOPcode wrote:
...but in America, you're not allowed to thrust, moan or see anything...

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