Re: Generic type passed into method question - C# Discussion Boards

OriginalGriff10-Dec-17 23:32

10-Dec-17 23:32

And?
What have you done so far?
Where are you stuck?
What help do you need?

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Mycroft Holmes10-Dec-17 23:39

Mycroft Holmes

10-Dec-17 23:39

OriginalGriff wrote:
What help do you need?

Well duh - send the codez NOW!

Never underestimate the power of human stupidity
RAH

OriginalGriff10-Dec-17 23:43

10-Dec-17 23:43

That was my guess: "I want you to do my homework" but it'd be nice to know if he's genuine and wants to think or just waste his whole life ... Big Grin | :-D

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Generic type passed into method question

phil.o11-Dec-17 18:02

phil.o

11-Dec-17 18:02

Democracy's in danger! Smile | :)

"I'm neither for nor against, on the contrary." John Middle

User987439-Dec-17 20:44

9-Dec-17 20:44

I'd like to start using more C# generics. Can someone tell me what the

<?>

portion of the method syntax below represents? Is it a placeholder for the object type? (see my example further down)

<Access Specifier> <Return Type> <Method Name><?>(Parameter List) 
{
   Method Body
}

I was wanting to do something like this, so that I could pass either an OLEDB DB Connection object or an SqlClient connection object.

private T DataConnection<T> ( T db_conn_obj , int index_of_mydatafile )
{
...
}

OriginalGriff9-Dec-17 22:32

9-Dec-17 22:32

The "bit in the middle" is the indicator that this is a Generic method, and allows you to specify a substitution name which identifies where the generic class type is needed. It doesn't have to be <T> - you can use any valid identifier:

private TypeOfClass DataConnection<TypeOfClass>(TypeOfClass db_conn_obj, int index_of_mydatafile)
    {
    return db_conn_obj;
    }

But the convention is to use "T" as the generic class name.
The trouble with that is I can happily pass any class type to your method:

var x = DataConnection("hello", 666);

And it will work - additionally, You can't use any of the fields, properties, or methods of your Connection, even if you pass an SqlConnection object.

The solution is to apply a constraint:

private T DataConnection<T>(T db_conn_obj, int index_of_mydatafile) where T: System.Data.Common.DbConnection
    {
    Console.WriteLine(db_conn_obj.ConnectionString);
    db_conn_obj.Open();
    return db_conn_obj;
    }

Which limits the classes you can pass to those derived from DbConnection (which includes SqlConnection, OleDbConnection, and so forth:

var x = DataConnection(new SqlConnection(), 666);
var y = DataConnection(new OleDbConnection(), 666);

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User9874310-Dec-17 0:49

10-Dec-17 0:49

This is a big help! I've been working on it for hours. I'm working on some existing code that I'm supposed to make work with both OleDbConnection as well as SqlConnection.

It's more of a training exercise for me, because it looks like it's going to take a lot of time to convert all of the db methods to use either connection.

So right now, I have an OleDbConnection, like so:

private OleDbConnection DataConnection ( int index_of_mydatafile )
{
    string dbpath = MyDataFiles[ index_of_mydatafile ];

    string conn_string = OledbProvider(dbpath) + "data source=" + dbpath;

    Debug.WriteLine ( conn_string );

    return new OleDbConnection ( conn_string );

}

The connection is just be declared and instantiated in a using statement like this:

using ( OleDbConnection dbConnection = DataConnection ( index_of_mydatafile ) )
			using ( OleDbCommand dbCommand = new OleDbCommand ( sql , dbConnection ) )
			using ( OleDbDataAdapter adapter = new OleDbDataAdapter ( dbCommand ) )

So the command object is actually opening the connection later. To get this working, I tried this, but I'm stuck at the new declaration, which is causing an error, presumably because I need to cast the T maybe? I'm just pulling things out of thin air now. lol

private T DataConnection<T> ( T db_conn_obj , int index_of_mydatafile ) where T : System.Data.Common.DbConnection
		{
			string dbpath = MyDataFiles[ index_of_mydatafile ];
			string provider = OledbProvider ( dbpath );
			string conn_string =  provider + "data source=" + dbpath;

			Debug.WriteLine ( conn_string );

			if ( provider == "" )
			{
				conn_string = @"Data Source= xxxx\xxxx;Initial Catalog=xxxx;Integrated Security=SSPI;Connect Timeout=5;ConnectRetryCount=0;ApplicationIntent=ReadWrite;"
			}
	
			return new T ( conn_string );
		}

OriginalGriff10-Dec-17 0:57

10-Dec-17 0:57

Ah! To create a new instance, you need to tell it that the only classes that can be "generic-ed" are concrete classes (like OldedbConnection, and SqlConnection), not abstract classes like DbConnection.
That's easy: add the new constraint (and remove the class instance from the parameters list):

private T DataConnection<T>(int index_of_mydatafile) where T : System.Data.Common.DbConnection, new()
    {
    T db_conn_obj = new T();
    db_conn_obj.ConnectionString = "...";
    db_conn_obj.Open();
    return db_conn_obj;
    }

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User9874310-Dec-17 1:05

10-Dec-17 1:05

Holy crap, man! That's freak'n awesome! It's a double ++ because the original code doesn't include the class instance in the parameters list.

This is the first time I actually posted a question on any programmer's forum. I wish I had done this sooner.

I really appreciate it.

OriginalGriff10-Dec-17 1:49

10-Dec-17 1:49

You're welcome!

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Eddy Vluggen10-Dec-17 3:03

Eddy Vluggen

10-Dec-17 3:03

RickBishop wrote:
I'm supposed to make work with both OleDbConnection as well as SqlConnection.

Could be done fairly easy without generics. See A short tale on two patterns that live in .NET[^].

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User9874310-Dec-17 18:41

10-Dec-17 18:41

This is very applicable. I will take a look. Thanks for sharing!

Eddy Vluggen11-Dec-17 2:34

Eddy Vluggen

11-Dec-17 2:34

You're welcome, and thanks Smile | :)

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2 Active Directory Questions

Gerry Schmitz10-Dec-17 1:04

Gerry Schmitz

10-Dec-17 1:04

What do you need, and what do the connections have in common?

You will find that OldDbConnection and SqlConnection (among others) inherit from Common.DbConnection (which also has an interface).

You can pass a class instance that another class "inherits" from (or an interface) if it meets your requirements instead of having to resort to generics (in this case).

"(I) am amazed to see myself here rather than there ... now rather than then".
― Blaise Pascal

Kevin Marois7-Dec-17 9:42

Kevin Marois

7-Dec-17 9:42

I'm very new to Active Directory, so bear with me please...

First
I'm using the following to validate a user:

public bool ValidateUser(Credentials credentials, string userName = "", string password = "")
{
    using (var context = new PrincipalContext(ContextType.Domain, credentials.ServerName, credentials.UserName, credentials.Password))
    {
        return context.ValidateCredentials(userName, password);
    }
}

But the ValidateCredentials takes the password in PLAIN TEXT and it works fine. This doesn't seem right. How is encryption handled? How do you encrypt the text and how does AD know the PW is encrypted?

Second
Next, I know that LDAP is a protocol. From what I see you specify LDAP in the
query string, as in "LDAP://OU=staffusers,DC=leeds-art,DC=ac,DC=uk"

Is this the way it's done? How do you specify another protocol to use?

Thanks

If it's not broken, fix it until it is.
Everything makes sense in someone's mind.
Ya can't fix stupid.

Dave Kreskowiak7-Dec-17 13:11

Dave Kreskowiak

7-Dec-17 13:11

1) You don't encrypt the text. You're correct is questioning "how does AD know the PW is encrypted?". It doesn't. The function you're calling is running on your machine, not the server. The method hashes the password for you, gets the encrypted account details, including password, from the domain controller and makes the comparison locally. The password never leaves the machine.

2) Go through this: Howto: (Almost) Everything In Active Directory via C#[^]

System.ItDidntWorkException: Something didn't work as expected.

C# - How to debug code[^].
Seriously, go read these articles.

Dave Kreskowiak

Kevin Marois8-Dec-17 5:13

Kevin Marois

8-Dec-17 5:13

Dave Kreskowiak wrote:
1) You don't encrypt the text. You're correct is questioning "how does AD know the PW is encrypted?". It doesn't. The function you're calling is running on your machine, not the server. The method hashes the password for you, gets the encrypted account details, including password, from the domain controller and makes the comparison locally. The password never leaves the machine.

I figured that's what happening. Do you know of any docs that state this?

If it's not broken, fix it until it is.
Everything makes sense in someone's mind.
Ya can't fix stupid.

Dave Kreskowiak8-Dec-17 7:29

Dave Kreskowiak

8-Dec-17 7:29

Only the training materials I had way back in the day.

System.ItDidntWorkException: Something didn't work as expected.

C# - How to debug code[^].
Seriously, go read these articles.

Dave Kreskowiak