如何查询TFDMemTable

Question

我正在尝试创建一个简单的循环来处理TFDMemTable。我已经在表单上放置了一个TFDMemTable、一个TFDQuery和一个TFDConnection，我想我已经正确地连接了所有内容，但是当我激活查询时，它会返回一条错误消息，指出没有FDMemTable1这样的表。

以下是我正在尝试的演示代码：

#include <vcl.h>
#pragma hdrstop
#include "Unit2.h"
#include "FireDac.Stan.Def.hpp"
//---------------------------------------------------------------------------
#pragma resource "*.dfm"
TForm2 *Form2;
//---------------------------------------------------------------------------
void __fastcall TForm2::FormCreate(TObject *Sender)
{
    FDMemTable1->InsertRecord(ARRAYOFCONST((L"Vic", 100, 30)));
    FDMemTable1->InsertRecord(ARRAYOFCONST((L"Jeong", 20, 20)));
    FDMemTable1->InsertRecord(ARRAYOFCONST((L"Christina", 400, 50)));
    FDMemTable1->InsertRecord(ARRAYOFCONST((L"Justina", 0, 60)));

    FDConnection1->ConnectionName = L"FDMemTable1";
    FDConnection1->DriverName = L"SQLite";
    FDConnection1->Connected = true;
    FDQuery1->Connection = FDConnection1;
}
//---------------------------------------------------------------------------
void __fastcall TForm2::Button1Click(TObject *Sender)
{
    UnicodeString x;
    FDQuery1->SQL->Text = "SELECT * FROM FDMemTable1";
    FDQuery1->Active = true;

    if (!FDQuery1->Eof) {
        x = FDQuery1->FieldByName(L"FullName")->AsString;
        
        ...

        FDQuery1->Next();
    }
}

如何查询现有的TFDMemTable

Answer 1

要查询FDMemTable，您可以使用FireDAC的LocalSQL工具。将TFDLocaSQL组件添加到窗体使您能够注册一个或多个TDataSet派生数据集(使用其Datasets属性的Add方法)，例如您的FDMemTable，以使用Sqlite实现将其注册为SQL搜索的目标。它应该足以执行您的查询，并且非常容易使用，一旦您设置好它。

有关详细信息，请参阅https://docwiki.embarcadero.com/RADStudio/Sydney/en/Local_SQL_(FireDAC)。

这是我的一个答案中的代码，它使用了带有FDMemTable的FireDAC的localSQL。代码是用Dellphi编写的，但转换成c++应该很简单：

  FDConnection1.DriverName := 'SQLite';
  FDConnection1.Connected := True;

  FDLocalSQL1.Connection := FDConnection1;
  FDLocalSQL1.DataSets.Add(FDMemTable1);

  FDLocalSQL1.Active := True;

  FDQuery1.SQL.Text := 'select * from FDMemTable1 order by ID limit 5';
  FDQuery1.Active := True;

Answer 2

实际的答案是如MartynA所说的那样。以下是最终运行的代码：

#include <vcl.h>
#pragma hdrstop
#include "Unit2.h"
#include "FireDac.Stan.Def.hpp"
//---------------------------------------------------------------------------

#pragma package(smart_init)
#pragma link "AdvGrid"
#pragma link "AdvObj"
#pragma link "AdvUtil"
#pragma link "BaseGrid"
#pragma link "DBAdvGrid"
#pragma resource "*.dfm"
TForm2 *Form2;
//---------------------------------------------------------------------------
void __fastcall TForm2::FormCreate(TObject *Sender)
{
    FDMemTable1->Active = true;
    FDMemTable1->InsertRecord(ARRAYOFCONST((L"Vic", 100, 30)));
    FDMemTable1->InsertRecord(ARRAYOFCONST((L"Jeong", 20, 20)));
    FDMemTable1->InsertRecord(ARRAYOFCONST((L"Christina, 400, 50)));
    FDMemTable1->InsertRecord(ARRAYOFCONST((L"Justina", 0, 60)));

    FDConnection1->ConnectionName = L"FDMemTable1";
    FDConnection1->DriverName = L"SQLite";
    FDConnection1->LoginPrompt = false;
    FDConnection1->Connected = true;

    FDLocalSQL1->Connection = FDConnection1;
    FDLocalSQL1->DataSets->Add(FDMemTable1, L"FDMemTable1");
    FDLocalSQL1->Active = true;

    FDQuery1->Connection = FDConnection1;
}

//---------------------------------------------------------------------------
void __fastcall TForm2::Button1Click(TObject *Sender)
{
    UnicodeString x;
    FDQuery1->SQL->Text = "SELECT * FROM FDMemTable1";
    FDQuery1->Active = true;

    if (!FDQuery1->Eof) {
        x = FDQuery1->FieldByName(L"FullName")->AsString;

        FDQuery1->Next();
    }
}