Title: How to quickly copy a record from one DataSet to another
Question: Frequently, in a database application, you must copy records from one dataset to another. You could always acomplish this task with a COBOL approach, copying every field painfully. But you are a Delphi programmer, and you can do it gracefully with just one command.
Answer:
Usually, you can acomplish this task using TBatchMove component. But there are some situations where TBatchMove doesn't fit:
- imagine that you don't want to copy all records, and don't want to use filters.
- you want to use the destination dataset validation events (BeforePost, OnValidate, etc)
- or even worse, the datasets structures are different.
The solution can be done in a simple procedure: you just have to copy all fields with the same name from one dataset to another. But there are some pitfalls:
- you can't copy Lookup and CalcFields
- you should use Assign when fields have the same name but have different datatype.
- your destination field can't be readonly.
procedure CopyRecord(Source, Destination: TDataSet);
var Ind:longint;
SField, DField: TField;
begin
for Ind:=0 to Source.FieldCount - 1 do
begin
SField := Source.Fields[ Ind ];
DField := Destination.FindField( SField.FieldName );
if (DField nil) and (DField.FieldKind = fkData) and
not DField.ReadOnly then
if (SField.DataType = ftString) or
(SField.DataType DField.DataType) then
DField.AsString := SField.AsString
else
DField.Assign( SField )
end;
end;
Here an example using a COBOL or VB Approach:
DEST.Open;
ORIGIN.Open;
while not ORIGIN.Eof do
begin
if ORIGINTYPE.AsString = 'T' then
with ORIGIN do
begin
DEST.Append;
DEST.FieldByName('TYPE').AsString := ORIGINTYPE.AsString;
DEST.FieldByName('FIRSTNAME').AsString := ORIGINFIRSTNAME.AsString;
DEST.FieldByName('LASTNAME').AsString := ORIGINLASTNAME.AsString;
DEST.FieldByName('CPF').AsString := ORIGINCPF.AsString;
DEST.FieldByName('PARTY').AsString := ORIGINPARTY.AsString;
DEST.Post;
end;
ORIGIN.Next;
end;
The same solution using a Delphi elegant procedure:
DEST.Open;
ORIGIN.Open;
while not ORIGIN.Eof do begin
if ORIGINTYPE.AsString = 'T' then begin
DEST.Append;
CopyRecord( ORIGIN, DEST );
DEST.Post;
end;
ORIGIN.Next;
end;
This procedure works fine with TQueries, TClientDataSet and any other TDataset-descendents.
I hope this tip can be useful to other database programmers.
Health and Freedom,
Josir.