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Copy a dataset and its persistent fields at runtime

Posted on 2008-10-01
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Last Modified: 2012-05-05
I have a dataset (TZTable -- similar to other datasets like TTable)
where I have cretaed some persistent fields.

I need to make a copy of this table at runtime and only change 1 thing - the name of the copy.

Anybody know how I can copy including its persistent fields :)
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Question by:rfwoolf
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Expert Comment

by:ziolko
ID: 22618409
don't know this TZTable but I would try .Assign() method on fields collection

TTable has:
Table1.FieldList.Assign()
Table1.FieldDefs.Assign()


ziolko.
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Expert Comment

by:ziolko
ID: 22618700
and if you want make complete clone including data, I guess easiest way would be assign all properties like database name, table name, session name etc. to new table object and then call .Open

ziolko.
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by:rfwoolf
ID: 22644672
Hmm it's telling me FieldList.Assign is a readonly property.
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by:rfwoolf
ID: 22644831
When I said
"I need to make a copy of this table at runtime and only change 1 thing - the name of the copy."
I meant I need a copy of this "TTable" at runtime. I am not trying to duplicate a database table, I am trying to duplicate a dataset.
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by:rfwoolf
ID: 22644993
The answer appears to lie here from a Borland article:
http://groups.google.co.za/group/borland.public.delphi.objectpascal/browse_thread/thread/599c60dcac5cb7fd?pli=1
 

I'll be glad to explain what I did. 
I don't have my actual code here, it's at work. 
But I started looking at 
http://www.borland.com/devsupport/delphi/ti/ 
under "Database Programming". 
The TI1467D 3/31/99 Dynamically creating a TTable & fields at runtime 
contained most of the solution. 
The interesting part was this code: 
==========quote begin========== 
{ Create a calculated TField, assign properties, 
      and add to MyTable's field definitions array. } 
      TaxAmount := TFloatField.Create(MyTable); 
      with TaxAmount do 
      begin 
        FieldName := 'TaxAmount'; 
        Calculated := True; 
        Currency := True; 
        DataSet := MyTable; 
        Name := MyTable.Name + FieldName; 
        MyTable.FieldDefs.Add(Name, ftFloat, 0, false); 
      end; 
    end; 
==========quote end========== 
The TI contains some different lines for creating non calculated fields, but 
the above code snippet turns out to be able to create calculated as well as 
non calculated fields. 
The TI defines this: 
var 
    TaxAmount: TFloatField; 
but I ended up defining a generic TField like this: 
var 
    MyField: TField; 
 
So then I loop thorugh the SourceDataSet's Fields: 
  for i := 0 to SourceDataSet.FieldCount - 1 do 
and depending on the Fields DataType property I created the fields using 
      MyField := TFloatField.Create(MyTable); 
      MyField := TIntegerField.Create(MyTable); 
      MyField := TStringField.Create(MyTable); 
or whatever using a case statement. 
After creating the field, all that now remains is to set up the TField 
properties as desired (copying the properties from the 
SourceDataSet.Fields[i]), and as the last thing, add it to the table: 
        MyTable.FieldDefs.Add(MyField.Name, MyField.DataType, MyField.Size, 
MyField.Required); 
To set up certain properties it's nescessary to use a case statement again: 
case SourceDataSet.Fields[i].DataType of 
  ftFloat: TFloatField(MyField).DisplayFormat := ',0'; 
{and so on} 
end; 
 
That's about it, as far as I remember. 
There is probably a lot of typos in this code, because I'm writing it from 
memory, so consider yourself warned! 
And maybe there is an easier way to do it, but this worked for me. 
 
Finn Tolderlund. 

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Author Comment

by:rfwoolf
ID: 22645367
Auurghh... still not winning. and there's so little information on the net.
Looking at the DFM of my form with the TTable I see that all it has is "objects" with name, fieldtype, and 1 or 2 other properties.  I don't know if I should be updating FieldDefs or FieldLists or just adding objects..
I have tried 2 methods of cloning -- 1 is to copy to clipboard at runtime and paste but then the fields do not get copied -- 2 is to use a Stream and the fields still do not get copied.
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Accepted Solution

by:
rfwoolf earned 0 total points
ID: 22645657
I finally came right after looking through some related posts on EE:
http://www.experts-exchange.com/Programming/Languages/Pascal/Delphi/Q_20553395.html
Ziolko thanks for trying though :)
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