Question

我正在尝试创建一个包含整个查询（CRUD）的类，以供其他单位/表单调用和使用它。但是后来我遇到了一些错误。我正在使用Firebird作为数据库。

我不知道如何添加查询以在函数内执行。尝试在函数中输入查询代码时出现错误。

___success;

但是如果我在按钮触发过程中输入查询代码，就不会有错误。

unit AllClass;

interface

uses
Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, 
System.Classes, Vcl.Graphics, Vcl.Controls, Vcl.Forms, Vcl.Dialogs, 
FireDAC.Stan.Intf, FireDAC.Stan.Option,FireDAC.Stan.Error,FireDAC.UI.Intf, 
FireDAC.Phys.Intf, FireDAC.Stan.Def,FireDAC.Stan.Pool, FireDAC.Stan.Async, 
FireDAC.Phys, FireDAC.Phys.FB,FireDAC.Phys.FBDef, FireDAC.VCLUI.Wait, 
FireDAC.Stan.Param, FireDAC.DatS,FireDAC.DApt.Intf, FireDAC.DApt, Data.DB, 
FireDAC.Comp.DataSet,FireDAC.Comp.Client, Vcl.StdCtrls;

type
 TForm6 = class(TForm)
 FDConnection1: TFDConnection;
 EveryQuery: TFDQuery;
 procedure login(username,password:String);
 private
  { Private declarations }
 public
  { Public declarations }
end;

var
 Form6: TForm6;

implementation

procedure login(username,password:String);
begin
 EveryQuery.SQL.Clear;  //here error
end;
end.

如果您对此问题有任何解决方案或想法，请帮助我。

Answer 1

您的function login应该是function TForm6.Login，因为它被声明为表单本身的方法。您可以通过在表单类中（在私有或公共部分中，而不是在当前位置的地方）编写声明并单击 Ctrl + Shift + < kbd> C ，IDE将在implementation部分生成正确的代码。

您当前的代码：

procedure login(username,password:String);
begin
 EveryQuery.SQL.Clear;  //here error
end;

更正的代码：

procedure TForm6.login(username,password:String);
begin
 EveryQuery.SQL.Clear;  //here error
end;

Answer 2

您的login()过程被声明为TForm6类的成员，但是您不是实现作为类成员。您需要在TForm6.部分的login过程名称前面添加implementation，例如：

unit AllClass;

interface

uses
  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, 
  System.Classes, Vcl.Graphics, Vcl.Controls, Vcl.Forms, Vcl.Dialogs, 
  FireDAC.Stan.Intf, FireDAC.Stan.Option,FireDAC.Stan.Error,FireDAC.UI.Intf, 
  FireDAC.Phys.Intf, FireDAC.Stan.Def,FireDAC.Stan.Pool, FireDAC.Stan.Async, 
  FireDAC.Phys, FireDAC.Phys.FB,FireDAC.Phys.FBDef, FireDAC.VCLUI.Wait, 
  FireDAC.Stan.Param, FireDAC.DatS,FireDAC.DApt.Intf, FireDAC.DApt, Data.DB, 
  FireDAC.Comp.DataSet,FireDAC.Comp.Client, Vcl.StdCtrls;

type
  TForm6 = class(TForm)
    FDConnection1: TFDConnection;
    EveryQuery: TFDQuery;
  private
    { Private declarations }
  public
    { Public declarations }
    function login(username, password: String): boolean;
  end;

var
  Form6: TForm6;

implementation

{$R *.dfm}

function TForm6.login(username, password: String): boolean;
begin
  Result := False;
  if (username <> '') and (password <> '') then
  begin
    //use parameter method
    EveryQuery.Close;
    EveryQuery.SQL.Text := 'Select 1 from MYGUESTS where FIRSTNAME = :theID and Password = :thePsw';
    EveryQuery.ParamByName('theID').AsString := username;
    EveryQuery.ParamByName('thePsw').AsString := password;
    EveryQuery.Open;
    Result := not EveryQuery.Eof;
    EveryQuery.Close;
    if not Result then
      ShowMessage('Wrong username or password. Please re-enter');
  end else
  begin
    ShowMessage('Please enter something');
  end;
end;

end.

然后您可以这样称呼它：

procedure TForm1.LogInClick(Sender: TObject);
begin
  if Form6.login(Username.Text, Password.Text) then
  begin
    Username.Clear;
    Password.Clear;
    Form3.Show;
    Hide;
  end;
end;

如何在函数内添加查询

2 个答案: