delphi FDMemtable中如何在已有的字段数据集上加入字段

//在原有数据集上是加不进去的。可以再做一个FDMemtable，然后

FDMemTable_新数据集.FieldDefs.Assign(DataSet_原数据集.FieldDefs);

FDMemTable_新数据集.FieldDefs.Add('新加字段', ftFloat);

FDMemTable_新数据集.CreateDataSet; //建立数据集

//将数据转移过来

FDMemTable_新数据集.CopyDataSet(DataSet_原数据集[coAppend]);

while not FDMemTable_新数据集.eof do

begin

FDMemTable_新数据集.edit;

//给新字段赋值或者用计算字段显示赋值。

FDMemTable_新数据集.Post;

FDMemTable_新数据集.next;

end;

其他人写的代码：

procedure TForm1.AddFieldTest;

var

DataFN : String;

TempMemTable : TFDMemTable;

begin

// Added, to avoid relative path for data file name

DataFN := ExtractFilePath(Application.ExeName) + 'Data.Xml';

FDMemTable1.FieldDefs.Add('ID', ftInteger, 0, false);

FDMemTable1.FieldDefs.Add('name', ftString, 30, false);

FDMemTable1.FieldDefs.Add('QualityID', ftInteger, 0, false);

FDMemTable1.CreateDataSet;

// i fill the the table with some value

FDMemTable1.Open;

FDMemTable1.AppendRecord([1, 'Movie1', 1]);

FDMemTable1.AppendRecord([2, 'Movie2', 2]);

FDMemTable1.AppendRecord([3, 'Movie3', 1]);

// after seeing the value on the grid, i push a button and save the table as XML

FDMemTable1.saveToFile(DataFN);

// Added, close the dataset and clear the FieldDefs

// Without the FieldDefs.Clear call, your code produces a "Duplicate field ID" error

FDMemTable1.Close;

FDMemTable1.FieldDefs.Clear;

// now after closing the program and running it again, i want to load the data with a new FieldDef Called Episode with a default value 0

// the table is connected to cxGrid, and the moment i try to load, i get the error i mentioned.

FDMemTable1.FieldDefs.Add('ID', ftInteger, 0, false);

FDMemTable1.FieldDefs.Add('name', ftString, 30, false);

// this line is NEW

FDMemTable1.FieldDefs.Add('Episode', ftInteger, 0, false);

FDMemTable1.FieldDefs.Add('QualityID', ftInteger, 0, false);

FDMemTable1.CreateDataSet;

// check the FieldCount and existence of the Episode field

Caption := IntToStr(FDMemTable1.FieldCount);

Assert(FDMemTable1.FindField('Episode') <> Nil);

// Create a temporary TFDMemTable

TempMemTable := TFDMemTable.Create(Nil);

try

// load the data into the temporary TFDMemTable

TempMemTable.loadFromFile(DataFN);

// copy the data from the temporary TFDMemTable into FDMemTable1

FDMemTable1.CopyDataSet(TempMemTable, [coAppend]);

// check the FieldCount and existence of the Episode field

Caption := IntToStr(FDMemTable1.FieldCount);

Assert(FDMemTable1.FindField('Episode') <> Nil);

finally

TempMemTable.Free;

end;

来源：https://blog.csdn.net/lyf_lyf/article/details/98631026

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