Question

标题几乎说明了一切。我使用TClientDataset存储对象数组，其中一个对象的成员定义为枚举类型。据我所知，Delphi集是位域，其大小可以在1到32个字节之间变化，具体取决于它们包含多少数据，而Delphi没有定义TSetField。我应该使用什么样的字段来加载这个值？

Answer 1

您可以使用TBytesField或TBlobField

ClientDataSet1MySet：TBytesField，Size = 32

var
  MySet: set of Byte;
  Bytes: array of Byte;
begin
  MySet := [1, 2, 4, 8, 16];

  // Write
  Assert(ClientDataSet1MySet.DataSize >= SizeOf(MySet), 'Data field is too small');

  SetLength(Bytes, ClientDataSet1MySet.DataSize);
  Move(MySet, Bytes[0], SizeOf(MySet));
  ClientDataSet1.Edit;
  ClientDataSet1MySet.SetData(@Bytes[0]);
  ClientDataSet1.Post;

  // Read
  SetLength(Bytes, ClientDataSet1MySet.DataSize);
  if ClientDataSet1MySet.GetData(@Bytes[0]) then
    Move(Bytes[0], MySet, SizeOf(MySet))
  else
    MySet := []; // NULL
end;

Answer 2

您可以将它们转换为字节，如下所示：

var
  States : TUpdateStatusSet; // Can be any set, I took this one from DB.pas unit
  SetAsAInteger: Integer;
  dbs: Pointer; // Here's the trick
begin
  States := [usModified, usInserted]; // Putting some content in that set
  dbs := @States;
  SetAsAInteger := PByte(dbs)^;
  //Once you got it, SetAsAInteger is just another ordinary integer variable.
  //Use it the way you like.
end;

从任何地方恢复：

var
  MSG: string;
  Inserted, Modified: string;
  States: TUpdateStatusSet;
  MySet: Byte;

begin
  while not ClientDataSet.Eof do
  begin
    //That's the part that interest us
    //Convert that integer you stored in the database or whatever 
    //place to a Byte and, in the sequence, to your set type.
    iSet := Byte(ClientDatasetMyIntegerField);// Sets are one byte, so they
                                              //  fit on a byte variable  
    States := TUpdateStatusSet(iSet);
    //Conversion finished, below is just interface stuff


    if usInserted in States then
      Inserted := 'Yes';
    if usModified in States then
      Modified := 'Yes';
    MSG := Format('Register Num: %d. Inserted: %s. Modified:%s',
                  [ClientDataSet.RecNo, Inserted, Alterted]);
    ShowMessage( MSG );
    ClientDataset.Next;
  end;

end;

Answer 3

基于安德烈亚斯的例子，但使恕我直言更简单明了。

在XE2上测试

您可以使用TBytesField或TBlobField

ClientDataSet1MySet：TBytesField，Size = 32

1）写作

var
  MySet: set of Byte;
  Bytes: TBytes;
begin
  MySet := [0];

  // Write
  Assert(ClientDataSet1Test.DataSize >= SizeOf(MySet), 'Data field is too small');

  SetLength(Bytes, ClientDataSet1Test.DataSize);
  Move(MySet, Bytes[0], SizeOf(MySet));
  ClientDataSet1.Edit;
  ClientDataSet1Test.AsBytes := Bytes;
  ClientDataSet1.Post;
end;

2）阅读

var
  MyResultSet: set of Byte;
begin
  Move(ClientDataSet1Test.AsBytes[0], MyResultSet, ClientDataSet1Test.DataSize);
end;

在数据集中存储Delphi集的最佳方法是什么？

3 个答案: