Re: How to apply Read lock to Record in VB 6.0 - Visual Basic Discussion Boards

Samir Ibrahim wrote:
one says it is good practice and I should use it.

No, you shouldn't.

Samir Ibrahim wrote:
Is using it considered Best Practice? (Just yes/No)

No. Not any more.

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Dave Kreskowiak
Microsoft MVP
Visual Developer - Visual Basic
2006, 2007, 2008

Thank you for the confirmation.

Samir R. Ibrahim

On the variable naming, it's a matter of preference really and if you can consistently get a group of devs to follow a standard. I've been in groups where everything is prefixed and in perfect Hungarian notation, and others where it was absolute chaos.

Any more if it's a project I'm doing solo, I use a 1 letter prefix on a value data types (Dim lCount as Long = 0L) and no prefix/notation with reference types; else I go with the flow and use whatever the standards are for the particular project/group.

Strict + Explicit = always ON.

My 2 cents... you ask 10 developers, expect 10 diff. answers - lol.

Any suggestions, ideas, or 'constructive criticism' are always welcome.

"There's no such thing as a stupid question, only stupid people." - Mr. Garrison

Jon_Boy wrote:
On the variable naming, it's a matter of preference really

This is a golden sentence.

in vfp it is Best Practice. in vb6 or vb.net it is matter of preference

Jon_Boy wrote:
My 2 cents... you ask 10 developers, expect 10 diff. answers - lol.

I will say if you ask 10 Developer, you will get 20 answer

I speak for my self when I am doing a large project is totally different from doing medium project and small project.

In large project I add my own prefixing to understand and quickly understand this variable, Public, Local, Private, where it came from (a form object, table, memory variable, reference, type, enum etc...

Where if you have lot of forms and lot of variable, and this variable should be public so the other variable in other form can take it is value.

end of line? in VFP I have 3 type of prefixing I follow.

In vb.net, I don't know yet if I will need that, since I am still in creating testing small projects (learning).

But from this thread (so far) I guess I will not.

Samir R. Ibrahim

Hi to All,
Here I come across a problem with CR.
When I run a specific query(joining two table) in MS access it works fine. But same query is repeating the resultant records twice. The query is as follows..

Dim qry1 As String = "SELECT distinct student.id, student.fname,student.lname, no_of_class_per_batch.no_of_class_held, student.no_of_class_att FROM (student INNER JOIN no_of_class_per_batch ON student.bid = no_of_class_per_batch.batch_id) where student.bid = '" & str & "'"

I am using vb.net2005 with Crystal Report.

Regards,
mahalakshmi

I am using Visual Basic 6.0 with MS Access in multiuser environment with DAO, I am trying to apply read lock on record, when the record is opened by another user, but not successful in doing so...Does any body know how this can be done what cursor type and lock type should be used for this purpose.

Why do you still use VB6 in 2009? Noone will asnwer you on that question. let me tell why i dont use VB6

Here are my reasons:

1. It will not be updated or supported by Microsoft

Microsoft has made it clear that they will not release any new versions of Classic VB either as part of Visual Studio .NET or standalone. Furthermore, they won’t be releasing new patches or fixes for it. This means that if a new security problem is found tomorrow the most likely advice Microsoft will give will be, “Upgrade to .NET to fix the problem.” No amount of complaints, unflattering press, online petitions will change this. .NET is where Microsoft wants Windows developers to be so that’s what they’re going to promote, come hell or high water.

2. It is outdated technology

As I mentioned above, VB6 was released in 1998. A lot has changed since then, particularly with the continued rise and importance of the Internet. Sure, there are a lot of things VB6 could do Web-wise but, unfortunately, there are newer tools, such as .NET, Ruby on Rails, and Java, that are new and/or have been updated to take advantage of the most recent trends while VB6 has languished.

Also, Windows has continued to change. With Vista, there are many things you have to do in order to use VB6 with it and to deploy VB6 apps to it that you didn’t have to do previously. Remember that when VB6 was released Windows 98 was brand new but now you would have to look around a lot to find systems still using it, particularly in businesses of any size. Changes to Windows promise only more troubles for VB6 applications going forward.

3. It is a career dead end

When you consider your career as a professional programmer you have to understand that not expanding your skill set beyond VB6 is a serious career limiting move. Fewer and fewer companies are hiring contractors and permanent employees for purely VB6 programming positions. And, to make matters worse, the positions that are available are often maintenance positions that offer little or no opportunity to develop new code. Instead developing new applications, you’re likely to be working on old, poorly written, applications that exhibit what I call the Winchester House effect from being patched and patched again by a legion of programmers over the years.

To make matters worse, these places are often unpleasant places to work, so much so that I’ve come to refer to them as “VB6 Ghettos”. You’ll often find them staffed with people who have little or no ambition to improve their skills, who jealously guard their ‘secret’ knowledge from you, and who are often lacking in application design skills. Nasty office politics reign supreme as people try to protect their position.

So those are my reasons why I think VB6 is dead as an application development tool for Windows programmers.

more info on the Death of VB read this

http://www.vb6.us/articles/microsofts-killing[^]

Hope it helps Smile | :)

Vuyiswa Maseko,

Few companies that installed computers to reduce the employment of clerks have realized their expectations.... They now need more and more expensive clerks even though they call them "Developers" or "Programmers."

C#/VB.NET/ASP.NET/SQL7/2000/2005/2008
http://www.vuyiswamaseko.tiyaneProperties.co.za
vuyiswam@its.co.za

The Lock Type

Imagine that, after creating a record set and working on it, you want to control who else can have access to the records of the set you are using. To exercise this control, you can create a "lock". This allows you, for example, to prevent other people from changing the records until you have finished with them. To support locking, the ADODB namespace is equipped with an enumeration named LockTypeEnum, which defines various options:

When a computer connects to a database, its user may need to make changes to various records at the same time, such as deleting a range of records or changing many records at the same time (such as giving a raise to many employees), instead of making one change, then another, then another. For this type of scenario, when the user accesses the records, instead of monopolizing them and waiting for the user to finish an operation that could take long, you can download the records on the user's computer, and disconnect the user from the database. The user would then make the necessary changes. When the user is ready to commit the changes, you can then reconnect to the data source and submit the changes. This type of lock is referred to as batch optimistic.
This lock is supported through the ADODB.LockTypeEnum.adLockBatchOptimistic value
You may have a database that a few different people access at the same time. If the database is small enough, which is the case for restricted environment, the likelihood of two people editing or updating the same record (at the same time) may be low. In this case, you can indicate that you want to lock the record only when necessary. In this case, you use what is referred to as optimistic locking.
This lock is implemented using the ADODB.LockTypeEnum.adLockOptimistic value
The above two options assume that you would lock many records to apply the indicated scenarios. If you prefer to lock one record at a time, you can use what is referred to as pessimistic locking.
This lock is done using the ADODB.LockTypeEnum.adLockPessimistic value
The above three scenarios allow a user to edit and/or update the records that are included in the set. In some cases, you may want to prevent any editing or update on the records while the set is being accessed. In this case, you can set the records to read-only.
This lock can be set using the ADODB.LockTypeEnum.adLockReadOnly value
If you don't want to specify the type of lock system to use on a record set, use the ADODB.LockTypeEnum.adLockUnspecified value, which is the default value. Otherwise, to specify the lock type, pass the desired value as the fourth argument to the RecordsetClass.Open() method. Here is an example:

Private Sub btnRecordset_Click(ByVal sender As System.Object, _
ByVal e As System.EventArgs) Handles btnRecordset.Click
Dim rstPeople As ADODB.RecordsetClass
Dim conADO As ADODB.ConnectionClass = New ADODB.ConnectionClass

rstPeople = New ADODB.Recordset
Dim fldEach As ADODB.Field

conADO.Open("Provider=Microsoft.Jet.OLEDB.4.0;" & _
"Data Source='C:\Programs\People.mdb'", Nothing, Nothing, 0)
rstPeople.Open("Persons", _
conADO, _
ADODB.CursorTypeEnum.adOpenDynamic, _
ADODB.LockTypeEnum.adLockOptimistic)
rstPeople.Close()
End Sub
This uses the adLockOptimistic as the type of lock used on the recordset.

Though doing your own record locking has it's uses, it also has some very large pitfalls. Mainly, if your not VERY careful with the lock and only keep it in place as long as is minimumly necessary, you're in for some trouble.

First, most people who do this don't know what they're doing and just throw records locks around like mad and keeping them there for minutes at a time, sometimes longer. This can kill your app's performance and the database's and it'll destroy your app's scalability. Also, what happens when your app locks records in a table, then your app crashes?? How are the locks going to get released??

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Dave Kreskowiak
Microsoft MVP
Visual Developer - Visual Basic
2006, 2007, 2008

I am trying to filter fields in a table that contain percent (%) and apostrophe (') characters. I kow that to filter an apostrophe you need to add another apostrophe (''). However, when a text contains the percent (%) character in combination with an apostrophe (') character, an exception is thrown. Also, when using the % character in a filter string, it will be function as an "*" (fields starting or ending with). I need the % to be considered as a character whenever the % makes part of a string in the field. How can I address these issues?

The code below explains my question.

Dim TheTable As New DataTable
Dim col As New DataColumn("Col1")
TheTable.Columns.Add(col)
Dim TheRow As DataRow = TheTable.NewRow
TheRow("Col1") = "Filter me"
TheTable.Rows.Add(TheRow)
TheRow = TheTable.NewRow
TheRow("Col1") = "Filter me%"
TheTable.Rows.Add(TheRow)
TheRow = TheTable.NewRow
TheRow("Col1") = "Filter me'"
TheTable.Rows.Add(TheRow)
TheRow = TheTable.NewRow
TheRow("Col1") = "Filter me%'"
TheTable.Rows.Add(TheRow)
TheRow = TheTable.NewRow
Dim filteredrows() As DataRow

filteredrows = TheTable.Select("Col1 Like 'Filter me'")
MsgBox(filteredrows.Length)

'THE NEXT LINE WILL RETURN ALL RECORDS. I NEED ONLY THE RECORD ENDING WITH (OR CONTAINING) THE CHARACTER %
filteredrows = TheTable.Select("Col1 Like 'Filter me%'")
MsgBox(filteredrows.Length)

'THE NEXT LINE WILL RETURN TWO RECORDS (Filter me) and (Filter me'). I need it to return (Filter me') only
filteredrows = TheTable.Select("Col1 Like 'Filter me'''")
MsgBox(filteredrows.Length)

'THE NEXT LINE WILL THROW AND ERROR: "Error in Like operator: the string pattern 'Filter me%'' is invalid"
filteredrows = TheTable.Select("Col1 Like 'Filter me%'''")
MsgBox(filteredrows.Length)

To escape the %, so you are searching for a %, you will likely need to put brackets around the %. Placing a backslash before the % may also work, but I always go with the brackets. For example:

filteredrows = TheTable.Select("Col1 Like 'Filter me[%]'")

mbv800 wrote:
'THE NEXT LINE WILL RETURN ALL RECORDS. I NEED ONLY THE RECORD ENDING WITH (OR CONTAINING) THE CHARACTER %
filteredrows = TheTable.Select("Col1 Like 'Filter me%'")

You can use a character set for the % character:

Col1 Like 'Filter me[%]'

You can also use an escape character:

Col1 Like 'Filter me!%' escape '!'

Despite everything, the person most likely to be fooling you next is yourself.

Some languages like C++ and Java have mode for the graphics object called XORmode.
This makes the rubber banding easier. You just set the XORmode for the graphics object and it does the work.

In VB 2008, yes, it could be done but it looks like it is several times more effort.

I hope I am missing something.

Please help.

Thanks,

Stefan

Microsoft has a How-to in this very issue-

http://support.microsoft.com/kb/71488[^]

Take a look. Good luck!

Ranjit Viswakumar
Professional Services Specialist
http://hostmysite.com/?utm_source=bb

That's not for VB 9, that's for VB 3!

Despite everything, the person most likely to be fooling you next is yourself.

Use the DrawReversibleFrame method. Here you have examples and everything:

MSDN Library: ControlPaint..::.DrawReversibleFrame Method [^]

Despite everything, the person most likely to be fooling you next is yourself.

Hi all...

I am creating a small web-browser.I have almost completed my program.The remaining part is that when someone click on "bookmark" menustrip,it will store the url to a file (called as something.dat) and dynamically create a new menustrip of that url below "bookmark" menustrip (as same done with Internet Explorer "Add to Favourite" feature). Now anyone can access that url by clicking its menustrip item.
Please suggest me how can I do this.

Thanks.

Gagan

You add menuitems the same way you add controls to a form. You create an instance of the ToolStripMenuItem, set it's properties, wire up it's events, then add it to the Items collection of the parent you want it to show up under.

Dim newMenuItem As New ToolStripMenuItem
newMenuItem.Size = New Size(152, 22)
newMenuItem.Text = "Some &Menu Item"

AddHandler newMenuItem.Click, AddressOf MyMenuItemHandler

FileToolStripMenuItem.Items.Add( newMenuItem )

A guide to posting questions on CodeProject[^]

Dave Kreskowiak
Microsoft MVP
Visual Developer - Visual Basic
2006, 2007, 2008

I have a need to write code similar to the following:

Private Sub Block()
    Call Sub A(sender, e)
    Call Sub B(sender, e)
    Call Sub C(sender, e)
End Sub

where Subs A, B, & C have differing arguments.
Is this possible? If not, is there any way to do this?
I can supply specific code if necessary, but it can get
rather lengthy...

I appreciate any help. Big Grin | :-D

Hi,

pass the arguments to the containing sub, something along these lines (details may be wrong,
normally I don't write VB):

Private Sub Block(arg1 as type1, arg2 as type2)
    Call Sub A(arg1, arg2)
    Call Sub B(arg1, arg2)
    Call Sub C(arg1, arg2)
End Sub

Luc Pattyn [Forum Guidelines] [My Articles]

- before you ask a question here, search CodeProject, then Google
- the quality and detail of your question reflects on the effectiveness of the help you are likely to get
- use the code block button (PRE tags) to preserve formatting when showing multi-line code snippets

Thanks, I'll try that

Working with Active Directory in VB.NET
By Psycho-*Coder*-Extreme

Read atricle at:
href="http://www.codeproject.com/KB/system/active_directory_in_vbnet.aspx#_comments">http://www.codeproject.com/KB/system/active_directory_in_vbnet.aspx#_comments

Would like to know how this could be modified if possible to allow endusers to reset their own password when it has expired.

Allow for a questions/answer and maybe the last 4 of SSN. but allowing the user to reset password without providing to much security access to do so.

Is there already a VB.net ap or code that can do this?

Thanks
sd

Here's a dumb observation. If the password has expired, they either won't be able to login, or they'll be forced to change the password upon login, without using any of your code.

A guide to posting questions on CodeProject[^]

Dave Kreskowiak
Microsoft MVP
Visual Developer - Visual Basic
2006, 2007, 2008

I am calling a subroutine that starts with the following line:

Private Sub AddPayrollTable(ByVal TableCode As Integer, ByRef PayrollArray As String)

When this subroutine gets called I get an error that says "Object reference not set to an instance of an object."

This has lead me to believe that the array (PayrollArray) has not been initialized so I ask, how can I initialize an array that is a parameter in a subroutine?

Side note: When I reference the array directly in the AddPayrollTable subroutine instead of passing it as a parameter, I get no error.

Thanks,

Craig

"That rug really tied the room together."

craigmg78 wrote:
Private Sub AddPayrollTable(ByVal TableCode As Integer, ByRef PayrollArray As String)

Well, I see a couple of problems. The first parameter is passed as an Integer with the name "*Code". This leads me to believe it should be an enum, but I'm saying this based on very limited information. Right now, you're passing a "magic number" that offers no documention about what it means.

The second parameter is not being passed an array, but as a single String. Initializing an array is really mean to be done by the caller, not the callee. But, again, you haven't provided any information as to what this method does with the array and what the contents of the array is supposed to be, so it's difficult to say what the correct solution is.

A guide to posting questions on CodeProject[^]

Dave Kreskowiak
Microsoft MVP
Visual Developer - Visual Basic
2006, 2007, 2008