How to clone an object
Phil Hunt
a new object of the same type ?
Thanks
ralph
>I have a simple object I load up from DB, Is there a easy way to clone it to
>a new object of the same type ?
>
Probably not. <g>
Depends on what you mean by "clone", ie, how much of a duplicate/copy
do you need, or if you even need one?
Cloning 'data' always takes you into the realm of "Shallow Copies" or
"Deep Copies", but in some cases it isn't the data but the objects's
behavior or state we want to 'clone'. (The ADO Recordset.Clone is an
example of the latter.)
We need more information.
-ralph
phil hunt
the change just by reverting back to the clone.
"ralph" <nt_cons...@yahoo.net> wrote in message
news:haa166hspc24r3esj...@4ax.com...
ralph
>I am more interested in the data. As I am changing data, I want to 'undo'
>the change just by reverting back to the clone.
>
>
Don't know what your 'data' looks like, but assuming it is a group of
properties, this is often accomplished by storing the last value for
each of your properties/attributes as a backup. Which is something I
figure you have already considered. Takes a bit of work.
It means everytime you change something, you have to reassign the
'backup'. If for some reason you want to undo, you either have to
create new 'Undo' method for each value, or do a blanket 'put-back'.
So it depends on how and when you feel you might need to undo, and the
granularity - per item, per process, per run, etc.
Perhaps 'Serialization' would be something to look into. For objects
that actually refers to packaging up all the data/state, etc and
trasporting it, or storing it, so you can come back later and read the
info to recreate the object. But you can also simply considered the
serialized data as a backup.
Your object would have a 'Save' method, just before you planned to do
something dangerous, where it simply stores everything. Then an 'Undo'
on an Oops. <g>
This also has the advantage of being able to perform muliple undos.
For an example, I have often done this for disconnected
ADODB.Recordsets, by wrapping the Recordset with my own object. Then
use the contained Recordset.Save feature to store a copy to a file.
Bang around on the original Recordset, then if I have to go back,
reload a new from the file.
But again it depends on what is needed for YOUR problem domain.
Any option you chose will look like a lot of typing, thus not easy,
but once you pick a particular strategy, most of it will be
boiler-plate.
-ralph
ralph
wrote:
>On Mon, 9 Aug 2010 21:41:28 -0400, "phil hunt" <a...@abc.com> wrote:
>
>>I am more interested in the data. As I am changing data, I want to 'undo'
>>the change just by reverting back to the clone.
>>
>>
>
Another strategy that is occasionally useful, is based on a timeless
principle of programming: "There is no problem that can't be resolve
with another layer of indirection". <g>
Wrap your object with one that combines a factory with storage.
-ralph
phil hunt
you mean by 'factory'. I came across them in some other language, but not
VB6
"ralph" <nt_cons...@yahoo.net> wrote in message
news:4fe166538h1e7enbl...@4ax.com...
ralph
>It sounds too much like work. Maybe some other time. But I am curious what
>you mean by 'factory'. I came across them in some other language, but not
>VB6
>
A Factory pattern/method is where you define an interface for creating
an object, and then let it decide who and what to create. In your case
also providing a Proxy - a surrogate to control access to the object/s
created. eg, swapping out objects with the client being none the
wiser.
Factory (and Proxy) are what is called 'Design Patterns'. A way of
describing general reuseable software architecture.
http://en.wikipedia.org/wiki/Design_pattern_(computer_science)
and
http://en.wikipedia.org/wiki/Factory_method_pattern
A Factory/Proxy in this case, would be a mechanism to simply store
whole objects instead of serializing them.
-ralph
Jason Keats
> I am more interested in the data. As I am changing data, I want to 'undo'
> the change just by reverting back to the clone.
If you want to ignore all changes to your object, then the easiest thing
to do is simply throw it away and reload it from the database.
Cloning would probably mean you have to write code to serialise and
deserialise your object's state (unless you use Ralph's suggestion of
saving the ADO recordset you used to populate your object, to XML).
If, however, you needed to keep track of changes to each property - so
you can undo undo changes one property at a time - then you probably
want to keep a LIFO stack containing your changes.
Many use code generation (eg one class per table) to solve this sort of
problem, especially if similar code is required for many classes.
Nobody
news:%2333oQjB...@TK2MSFTNGP05.phx.gbl...
>I have a simple object I load up from DB, Is there a easy way to clone it
>to a new object of the same type ?
MZTools lists all properties of your classes when you use "Generate XML
Documentation". You need to copy them to Excel or similar program to extract
property names.
Also, the code below dumps a list of properties, methods, and events of your
class from Object Browser, so you can easily write code to save the
contents. It uses SendKeys and copy from the Clipboard. To use it, bring up
Object Browser(F2), then select your project name from the list, then click
on your class. You would see the list of properties on the right pan. Right
click anywhere and make sure that "Group Members" is selected. Click on the
first property on the right pan, then start a new VB IDE instance, add a
Timer to Form1, then add the code below. Run the project, and switch to the
VB IDE that is showing Object Browser. After 5 seconds, the running program
would capture property names and print them to the immediate window. From
there, you can copy them and do with them whatever you want.
Option Explicit
Private Sub Form_Load()
Timer1.Interval = 5000
End Sub
Private Sub Timer1_Timer()
Timer1.Enabled = False
DumpObjectBrowser
End Sub
Private Sub DumpObjectBrowser()
Dim Str As String
Dim LastStr As String
Dim Counter As Long
Clipboard.Clear
Counter = 0
Do
LastStr = Str
SendKeys "^c", True
Delay 0.1
Str = Clipboard.GetText
If LastStr = Str Then
' We reached the end
Exit Do
End If
Debug.Print Str
SendKeys "{DOWN}", True
Delay 0.1
Counter = Counter + 1
Loop Until Counter = 100
Me.Caption = "Done!"
End Sub
Private Sub Delay(ByVal Seconds As Single)
Dim t As Single
t = Timer
Do While Abs(Timer - t) < Seconds
DoEvents
Loop
End Sub
Phil Hunt
I am thinking about cloning the data, not the definition.
It is academic now. But can I use a Property bag in my situation. I seen it,
but never play with it.
"Nobody" <nob...@nobody.com> wrote in message
news:i3rmlh$c7r$1...@speranza.aioe.org...
ralph
>Intersting.
>I am thinking about cloning the data, not the definition.
>It is academic now. But can I use a Property bag in my situation. I seen it,
>but never play with it.
>
lol
VB's built-in serialization product.
Glad you stumbled across it. I'd forgotten about them, and you did ask
for "easy" too. Dop! <g>
Just a word of warning. Property Bags store data as Variants and as we
know VB is very obliging when it comes to coercing a value into a
Variant, or in coercing a value out of one. Dates and alphanumeric
strings can often be troublesome. So make sure you have clear business
rules for conversion. It also is useful to add additional "format" or
"type" properties to insure there are no misunderstandings.
-ralph
Dee Earley
The data in a property bag is typed, it may be implicit via the variant
type, but you do get out the same data type you put in.
--
Dee Earley (dee.e...@icode.co.uk)
i-Catcher Development Team
iCode Systems
(Replies direct to my email address will be ignored.
Please reply to the group.)
ralph
<dee.e...@icode.co.uk> wrote:
>
>The data in a property bag is typed, it may be implicit via the variant
>type, but you do get out the same data type you put in.
An absolute given.
I stand corrected, and the OP should ignore my advice as absolutely
nothing can ever go wrong.
-ralph
Phil Hunt
"ralph" <nt_cons...@yahoo.net> wrote in message
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