内存表 FDMemTable ClientDataSet CreateDataSet 动态创建字段

https://community.embarcadero.com/index.php/blogs/entry/firedac-in-memory-dataset-tfdmemtable

ClientDataSet FieldDefs Add Field CreateDataSet 动态创建字段

  FDMemTable1.Close();
  FDMemTable1.FieldDefs.Clear();
  FDMemTable1.FieldDefs.Add('ID', ftInteger, 0, True);
  FDMemTable1.FieldDefs.Add('Name', ftString, 20, false);
  FDMemTable1.CreateDataSet();
  FDMemTable1.AppendRecord([101, 'aaa']);
  FDMemTable1.AppendRecord([102, 'bbb']);
  FDMemTable1.AppendRecord([103, 'ccc']);

　　TFDMemTable *table= new TFDMemTable();

delete table;

void __fastcall TForm1::createField()
{
  ClientDataSet1->Close();

  ClientDataSet1->Fields->Clear();
  ClientDataSet1->FieldDefs->Clear();

  ClientDataSet1->Open();
  ClientDataSet1->Close();
  for(int i =  ;i < ClientDataSet1->Fields->Count ;i++)
   ClientDataSet1->Fields->Fields[]->Free();//释放所有的静态字段

  for(int i =  ;i < ClientDataSet1->FieldDefs->Count ;i++)
    ClientDataSet1->FieldDefs->Items[i]->CreateField(ClientDataSet1);

  TBooleanField *NewField;
  NewField = new TBooleanField(ClientDataSet1);
  NewField->FieldName="SelectMe";
  NewField->DisplayLabel = "选择";
  NewField->FieldKind=fkInternalCalc;
  NewField->DataSet=ClientDataSet1;
  NewField->Index = ;
  ClientDataSet1->Open();
}
void __fastcall TForm1::BitBtn1Click(TObject *Sender)
{
        sql = "select  from TABLE1 ";
        this->ADOQuery1->Close();
        this->ADOQuery1->SQL->Clear();
        this->ADOQuery1->SQL->Add(this->sql);
        this->ADOQuery1->Open();
        this->createField();
}

  cds1->Close();
  cds1->FieldDefs->Clear();
  cds1->FieldDefs->Add("ID", ftInteger, , true);
  cds1->FieldDefs->Add("Name", ftString, , false);
  cds1->FieldDefs->Add("DT", ftDateTime, , false);
  cds1->CreateDataSet();
  cds1->AppendRecord(  ARRAYOFCONST((,"aaa",Now().DateTimeString() )));
  cds1->AppendRecord(  ARRAYOFCONST((,"bbb",Now().DateTimeString() )));
  cds1->AppendRecord(  ARRAYOFCONST((,"ccc",Now().DateTimeString() )));

  ClientDataSet1.Close();
  ClientDataSet1.FieldDefs.Clear();
  ClientDataSet1.FieldDefs.Add('ID', ftInteger, , true);
  ClientDataSet1.FieldDefs.Add('Name', ftString, , false);
  ClientDataSet1.FieldDefs.Add('DT', ftDateTime, , false);
  ClientDataSet1.FieldDefs.Add('chk', ftBoolean, , false);
  ClientDataSet1.CreateDataSet();
  ClientDataSet1.Open;
  ClientDataSet1.Append;
  ClientDataSet1.FieldByName('id').Value := ;
  ClientDataSet1.FieldByName('name').Value := 'abc';
  ClientDataSet1.FieldByName('dt').Value := Now;
  ClientDataSet1.Post;
  ClientDataSet1.AppendRecord([,'bbb',Now()]);
  ClientDataSet1.AppendRecord([,'ccc',Now()]);

CreateDataSet

FDMemTable1->Close();
FDMemTable1->FieldDefs->Clear();
FDMemTable1->FieldDefs->Add("ID", ftInteger, , true);
FDMemTable1->FieldDefs->Add("Name", ftString, , false);
FDMemTable1->FieldDefs->Add("DT", ftDateTime, , false);
FDMemTable1->CreateDataSet();
FDMemTable1->AppendRecord(ARRAYOFCONST((, "aaa", Now().DateTimeString())));
FDMemTable1->AppendRecord(ARRAYOFCONST((, "bbb", Now().DateTimeString())));
FDMemTable1->AppendRecord(ARRAYOFCONST((, "ccc", Now().DateTimeString())));
FDMemTable1->First();

AddFieldDef

with CDS2 do
  begin
    with FieldDefs.AddFieldDef do
    begin
      DataType := ftInteger;
      Name := 'Field1';
    end;
    with FieldDefs.AddFieldDef do
    begin
      DataType := ftString;
      Size := ;
      Name := 'Field2';
    end;
    with IndexDefs.AddIndexDef do
    begin
      Fields := 'Field1';
      Name := 'IntIndex';
    end;
    CreateDataSet;

C++也可以这样写

TVarRec row[] = {user, password, purview, "", 0};
 int value_size =8;
 
qry->AppendRecord(row, value_size);

__fastcall TForm1::TForm1(TComponent* Owner)
    : TForm(Owner)
{
  TFieldDefs *pDefs = CDS2->FieldDefs;
  TFieldDef *pDef = pDefs->AddFieldDef();
  pDef->DataType = ftInteger;
  pDef->Name = "Field1";

  pDef = pDefs->AddFieldDef();
  pDef->DataType = ftString;
  pDef->Size = ;
  pDef->Name = "Field2";

  TIndexDef *pIDef = CDS2->IndexDefs->AddIndexDef();
  pIDef->Fields = "Field1";
  pIDef->Name = "IntIndex";

  CDS2->CreateDataSet();
}

2016.8.25  FDMemTable 试验成功 ，三种创建的方式都最终成了InternalCalcField字段。

ClientDataSet1->Close();

    ClientDataSet1->Fields->Clear();
    ClientDataSet1->FieldDefs->Clear();

    TFieldDef *fd;
    fd = ClientDataSet1->FieldDefs->AddFieldDef();
    fd->InternalCalcField = true;
    fd->Name = "calc1";
    fd->DataType = ftString;
    fd->Size = ;

    fd = ClientDataSet1->FieldDefs->AddFieldDef();
    fd->InternalCalcField = true;
    fd->Name = "flag";
    fd->DataType = ftBoolean;

    ClientDataSet1->FieldDefs->Add("ID", ftString, , false);
    ClientDataSet1->FieldDefs->Add("Name", ftString, , false);
    ClientDataSet1->FieldDefs->Add("DT", ftString, , false);
    ClientDataSet1->FieldDefs->Add("my", ftString, , false);
    ClientDataSet1->FieldDefs->Find("my")->InternalCalcField = true;

     for(int i =  ;i < ClientDataSet1->FieldDefs->Count ;i++)
    ClientDataSet1->FieldDefs->Items[i]->CreateField(ClientDataSet1);

      TBooleanField *NewField;
  NewField = new TBooleanField(ClientDataSet1);
  NewField->FieldName="SelectMe";
  NewField->DisplayLabel = "选择";
  NewField->FieldKind=fkInternalCalc;
  NewField->DataSet=ClientDataSet1;

//    ClientDataSet1->CreateDataSet(); 有了上面的CreateField，此句可不要。仅此句还不能创建fkInternalCalc字段，创建变成了fkData
    ClientDataSet1->Open();

    for (int i = ; i < ClientDataSet1->Fields->Count; i++)
    {

        ClientDataSet1->Fields->Fields[i]->FieldName;
        ClientDataSet1->Fields->Fields[i]->FieldKind;
    }

如果dfm窗体文件定义了字段，那么不用createDataSet了，只要open就可以了。

object ds1: TFDMemTable
    OnCalcFields = ds1CalcFields
    FieldDefs = <>
    CachedUpdates = True
    IndexDefs = <>
    FetchOptions.AssignedValues = [evMode]
    FetchOptions.Mode = fmAll
    ResourceOptions.AssignedValues = [rvSilentMode]
    ResourceOptions.SilentMode = True
    UpdateOptions.AssignedValues = [uvCheckRequired, uvAutoCommitUpdates]
    UpdateOptions.CheckRequired = False
    UpdateOptions.AutoCommitUpdates = True
    StoreDefs = True
    Left = 352
    Top = 160
    object ds1Field: TDateTimeField
      FieldName = aaa
    end
    object ds1Field2: TStringField
      FieldName = bbb
    end
    object ds1Field3: TStringField
      FieldName = ccc
    end

ds1->Close();

ds1->Open();