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TDataset.CopyFields

2024-11-27 00:39:39   203人阅读

Description

Often when manipulating datasets with similar structures, you need to copy the records from one dataset to another.  E.g. you may have fetched some records in a query or clientdaset and have located the matching records in another dataset.  You might then want to ensure the record values match without refetching the target dataset.
This looks like it would be easy to implement - i have rewritten it to take care of nested datasets as well as ordinary dataset fields.
Steps to Reproduce:
This is a requested new public method in the base TDataset class.
function TDataSet.CopyFields(Source: TDataSet): Integer;// copies matching fields in current records- returns number of fields copiedvar  FieldCtr: Integer;  DestField, SourceField: TField;begin  Result := 0;  for FieldCtr := 0 to Source.FieldCount - 1 do begin    SourceField := Source.Fields[FieldCtr];    Field := FindField(SourceField.FieldName);    if not Assigned(Field) then Continue;    if Field.ClassType = TDataSetField then begin  // nested datasets      while TDataSetField(Field).NestedDataSet.RecordCount > 0 do        TDataSetField(Field).NestedDataSet.Delete;      TDataSetField(SourceField).NestedDataSet.First;      while not TDataSetField(SourceField).NestedDataSet.Eof do begin        TDataSetField(Field).NestedDataSet.Append;        CopyFields(TDataSetField(Field).NestedDataSet, TDataSetField(SourceField).NestedDataSet);        TDataSetField(Field).NestedDataSet.Post;        TDataSetField(SourceField).NestedDataSet.Next;      end;     end else      Field.Value := SourceField.Value;    Inc(Result);  end;end;This would typically be used as follows:SourceDS.First;while not SourceDS.EOF do begin  if DestDS.Locate({info required to find matching record}) then begin    DestDS.Edit;    DestDS.CopyFields(SourceDS);    DestDS.Post;  end;  SourceDS.Next;end;

 

 

TDataset.CopyFields


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