如何在数据集中存储Delphi集合的最佳方法？

Question

标题已经说得很清楚了。我正在使用TClientDataset来存储对象数组，其中一个对象的成员定义为枚举类型的集合。据我所知，Delphi集合是位域，其大小可以根据它们包含的数据量从1到32个字节不等，而Delphi没有定义TSetField。我应该使用什么样的字段来加载这个值呢？

- Mason Wheeler

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请参阅如何保存/加载类型集？。 - NGLN

Answer 1

你可以使用 TBytesField 或 TBlobField。

ClientDataSet1MySet：TBytesField，大小=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;

- Andreas

---

1. 为了让你的示例更加清晰，我建议将 "ClientDataSet1MySet.SetData(@Bytes[0])" 改为 "ClientDataSet1MySet.AsBytes := Bytes"
2. 在 // Read 块中（在 Move 行上），我认为你必须将 "SizeOf(MySet)" 更改为 "ClientDataSet1MySet.DataSize" 以保持一致。

- Roeland Van Heddegem

Answer 2

你可以将它们转换为字节，像这样：

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;

- Fabricio Araujo

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这很好用，直到你需要超过32位。集合可以达到256位，而我处于可能需要大部分空间的情况下。 - Mason Wheeler

我会尝试将其适应那种情况。 - Fabricio Araujo

Answer 3

基于Andreas的例子，但在我看来更简单和清晰一些。

在XE2上进行了测试。

你可以使用TBytesField或TBlobField。

ClientDataSet1MySet：TBytesField，大小=32

1）写入

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;

- Roeland Van Heddegem