Calculated Field created in runtime

Diego Osorio

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Sep 1, 1998, 3:00:00 AM9/1/98

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I'm trying to attach a new calculated field to a TClientDataSet during
runtime. Does anyone have an idea on how to do this ??

Brian Bushay TeamB

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Sep 2, 1998, 3:00:00 AM9/2/98

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>'m trying to attach a new calculated field to a TClientDataSet during
>runtime. Does anyone have an idea on how to do this ??

here is an example
2) In the FormCreate, create your calculated field:
(For this example,use DBDEMOS/EMPLOYEE.DB)

Table1.Active:=false; // Must be false to add Fields to the Dataset
Table1.FieldDefs.Update; // Make sure we have the latest Fields

Monthly:=TFloatField.Create(Table1);
Monthly.FieldName:='Monthly Salary';
Monthly.Calculated:=true;
Monthly.Dataset:=Table1;
Monthly.DisplayFormat:='$#,0.00';

Table1.Active:=true;

--
Brian Bushay (TeamB)
Bbu...@DataGuidance.com

Roman Krejci

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Sep 2, 1998, 3:00:00 AM9/2/98

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Hi Brian,
this will work - but the prerecquisite is that
the table has persistentl physical fields.
if it has not, after the final open the table will have
FieldCount = 1 and will contain only
'Monthly Salary' field. If OnClacFields event refers
to any other fields, an exception will be thrown.
--
Roman
(please remove STOPSPAM. in header)
URL: www.rksolution.cz (Delphi corner)
MAIL: IN...@rksolution.cz

Brian Bushay TeamB wrote in message
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Diego Osorio

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Sep 2, 1998, 3:00:00 AM9/2/98

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Yes, Roman is right. I tried the code against my ClientDataSet (which is
created in memory only at runtime) and the end result is that there is only
one field in the DataSet.

I use a local client data set to contain the data provided by a SQL query.

ClientDataSet1 := TClientDataSet.Create( Application );
ClientDataSet1.Provider := sqlQry.Provider;
ClientDataSet1.OnCalcFields := SomeOnCalcFields;

sqlQry.Open;
ClientDataSet1.Open;

Is there any way to add a field to a dataset created this way or is there
any other approach that you recommend.

Roman Krejci

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Sep 2, 1998, 3:00:00 AM9/2/98

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The only way is to have persistent fields.
If you cannot add persistent fields at design time,
create them at runtime .

Brian Bushay TeamB

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Sep 3, 1998, 3:00:00 AM9/3/98

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>
>Is there any way to add a field to a dataset created this way or is there
>any other approach that you recommend.

You have to have persistant fields to add a calculated field. You can create
the pesistant fields in code too.
Here is another example

var
f : TField;
i : integer;
begin
Table1.Close;
//itterate through fields and create persistant fields
for i := 0 to Table1.FieldDefs.Count - 1 do
Table1.FieldDefs.Items[i].CreateField(Table1);
//create new calculated field
f := TStringField.Create(Table1);
f.Name := 'Table1CalcField';
f.FieldName := 'CalcField';
f.DisplayLabel := 'CalcField';
f.Calculated := True;
f.DataSet := Table1;
//open the table for use
Table1.Open;
end;

Diego Osorio

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Sep 8, 1998, 3:00:00 AM9/8/98

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Thank you very much. It works just the way I want it.

Brian Bushay TeamB wrote in message

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