TClientDataSet[27]: 字段值的约束(或叫输入限制)

Required、Precision、MaxValue、MinValue:

begin
  { Required: 必填字段 }
  with TIntegerField.Create(Self) do begin
    FieldName := 'ID';
    Required := True;
    DataSet := ClientDataSet1;
  end;

  { Precision: 浮点数精度}
  with TFloatField.Create(Self) do begin
    FieldName := 'Float';
    Precision := 3; { 譬如: 输入 1.2345 只会保留 1.23 }
    DataSet := ClientDataSet1;
  end;

  { MaxValue、MinValue }
  with TIntegerField.Create(Self) do begin
    FieldName := 'Integer';
    MinValue := 1;
    MaxValue := 99;
    DataSet := ClientDataSet1;
  end;

  ClientDataSet1.CreateDataSet;
end;

 
 
 
 
 

 

 
  

可在字段的 CustomConstraint 属性中按 SQL 语法指定约束规则;
并用字段的 ConstraintErrorMessage 属性指定违反规则后的错误提示.

procedure TForm1.FormCreate(Sender: TObject);
begin
  with TIntegerField.Create(Self) do begin
    FieldName := 'ID';
    CustomConstraint := 'x>0 and x<100'; { 其中的 x 是随意的, 表示当前字段值 }
    ConstraintErrorMessage := 'Err1';
    DataSet := ClientDataSet1;
  end;

  with TStringField.Create(Self) do begin
    FieldName := 'Name';
    Size := 11;
    CustomConstraint := 'x Like ''张%'''; { 假如只要姓张的 }
    ConstraintErrorMessage := 'Err2';
    DataSet := ClientDataSet1;
  end;

  with TStringField.Create(Self) do begin
    FieldName := 'Sex';
    Size := 2; { 如果使用 TWideStringField 这里应该是 1 }
    CustomConstraint := 'x in(''男'', ''女'')'; { 只能输入: 男或女 }
    ConstraintErrorMessage := 'Err3';
    DataSet := ClientDataSet1;
  end;

  with TStringField.Create(Self) do begin
    FieldName := 'Email';
    Size := 21;
    CustomConstraint := 'Lower(x) Like ''%@gmail.com'''; { 假如只能是 Google 信箱}
    ConstraintErrorMessage := 'Err4';
    DataSet := ClientDataSet1;
  end;

  ClientDataSet1.CreateDataSet;

  ClientDataSet1.AppendRecord([1, '张三', '男', '[email protected]']);
  ClientDataSet1.AppendRecord([2, '张四', '女', '[email protected]']);
end;

{ 禁用限制 }
procedure TForm1.Button1Click(Sender: TObject);
begin
  ClientDataSet1.DisableConstraints;
end;

{ 启用限制 }
procedure TForm1.Button2Click(Sender: TObject);
begin
  ClientDataSet1.EnableConstraints;
end;

 
 
 
 
 

 

 
  

使用数据集的 Constraints 属性重做上面的例子:

procedure TForm1.FormCreate(Sender: TObject);
begin
  with ClientDataSet1.FieldDefs do begin
    Add('ID', ftInteger);
    Add('Name', ftString, 11);
    Add('Sex', ftString, 2);
    Add('Email', ftString, 21);
  end;

  with ClientDataSet1.Constraints.Add do begin
    CustomConstraint := 'ID>0 and ID<100'; { 其中的 ID 是字段名 }
    ErrorMessage := 'Err1';
  end;

  with ClientDataSet1.Constraints.Add do begin
    CustomConstraint := 'Name Like ''张%''';
    ErrorMessage := 'Err2';
  end;

  with ClientDataSet1.Constraints.Add do begin
    CustomConstraint := 'Sex in(''男'', ''女'')';
    ErrorMessage := 'Err3';
  end;

  with ClientDataSet1.Constraints.Add do begin
    CustomConstraint := 'Lower(Email) Like ''%@gmail.com''';
    ErrorMessage := 'Err4';
  end;

  ClientDataSet1.CreateDataSet;

  ClientDataSet1.AppendRecord([1, '张三', '男', '[email protected]']);
  ClientDataSet1.AppendRecord([2, '张四', '女', '[email protected]']);
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
  ClientDataSet1.DisableConstraints;
end;

procedure TForm1.Button2Click(Sender: TObject);
begin
  ClientDataSet1.EnableConstraints;
end;

 
 
 
 
 

 

 
  

数据集的 Constraints 和字段的 CustomConstraint 也都可以在设计时完成.

不过其中的 ConstraintErrorMessage 和 ErrorMessage 在当前版本(14.0.3593.25826)中有 bug;
我在 Delphi 2007 中测试了一下, 没有问题.