[英]Delphi TClientDataset SQL Server RowVersion
Does anyone have any experience using SQL Server 's RowVersion
column with TClientDataset
? 有没有人有使用SQL Server的
RowVersion
列和TClientDataset
? Specifically, I need to get the RowVersion
value back on insert. 具体来说,我需要在插入时重新获得
RowVersion
值。 It seems to get the RowVersion
value back on updates but a newly inserted row it does not. 似乎在更新时重新获得了
RowVersion
值,但并没有获得新插入的行。
This seems to involve a similar problem to when you need to use a CDS with a SqlServer table which has an Identity field, where the value in the field is set by the server, so you don't know it during the CDS-side insert operation. 这似乎与需要将CDS与带有Identity字段的SqlServer表一起使用时的问题类似,该字段中的值由服务器设置,因此在CDS端插入期间您不知道它操作。 One way to do that is explained in this article http://edn.embarcadero.com/article/20847 .
本文http://edn.embarcadero.com/article/20847中介绍了一种实现此目的的方法。 It involves assigning a temporary, negative, value to the Identity field in the CDS in the
OnNewRecord
event, and then using the Refresh
method of the CDS to retrieve the server-side identity field value once the new record has been posted to the server by calling ApplyUpdates
. 它涉及在
OnNewRecord
事件中为CDS中的“标识”字段分配一个临时的负值,然后在新记录已通过以下方式发布到服务器后,使用CDS的Refresh
方法检索服务器端标识字段的值。调用ApplyUpdates
。
In D7, which I'm using for this answer as a sort of lowest common denominator, this technique seems to work fine to a RowVersion field as well. 在D7中,我将此答案用作最低公分母,该技术似乎也适用于RowVersion字段。 An extract from a sample project is below.
下面是一个示例项目的摘录。 To get it working, I had to define the RowVersion field as an
ftBytes
field with a size of 8, and to change the ProviderFlags
to exclude pfInWhere
and pfInUpdate
from the AdoQuery's identity field, ID. 为了使其正常工作,我必须将RowVersion字段定义为
ftBytes
字段,大小为8,并更改ProviderFlags
以从AdoQuery的标识字段ID中排除pfInWhere
和pfInUpdate
。
The RowVerStr
field in the CDS is just to display the value legibly in a TDBGrid. CDS中的
RowVerStr
字段只是为了在TDBGrid中清晰显示该值。
type
TForm1 = class(TForm)
ADOConnection1: TADOConnection;
ADOQuery1: TADOQuery;
DataSetProvider1: TDataSetProvider;
DataSource1: TDataSource;
DBGrid1: TDBGrid;
DBNavigator1: TDBNavigator;
ADOQuery1ID: TAutoIncField; // The ID field is an Identity field on the server
ADOQuery1IntValue: TIntegerField; // a user field
CDS1: TClientDataSet;
CDS1ID: TAutoIncField;
CDS1IntValue: TIntegerField;
CDS1RowVersion: TBytesField;
CDS1RowVerStr: TStringField; // just for display, fkInternalCalc, size = 20
ADOQuery1RowVersion: TBytesField;
procedure FormCreate(Sender: TObject);
procedure CDS1AfterPost(DataSet: TDataSet);
procedure CDS1AfterDelete(DataSet: TDataSet);
procedure CDS1NewRecord(DataSet: TDataSet);
procedure CDS1AfterInsert(DataSet: TDataSet);
procedure CDS1CalcFields(DataSet: TDataSet);
public
FID : Integer; // To generate temporary value for CDS identity field
function NextID : Integer;
end;
[...]
function GetRowVerString(V : Variant) : String;
var
i,
Dim,
Min,
Max : Integer;
i64 : Int64;
begin
Result := '';
if not VarIsArray(V) then Exit;
Dim := VarArrayDimCount(V);
Max := VarArrayHighBound(V, Dim);
Min := VarArrayLowBound(V, Dim);
for i := 0 to 7 do
Int64Rec(i64).Bytes[i] := V[i];
Result := IntToStr(i64);
end;
procedure TForm1.FormCreate(Sender: TObject);
begin
// CDS1ID is an ftAutoInc field, so we need to remove its read-only flag so
// that we can assign it a temporary negative value in the OnNewRecord event
CDS1ID.ReadOnly := False;
AdoQuery1RowVersion.ProviderFlags := AdoQuery1RowVersion.ProviderFlags - [pfInWhere, pfInUpdate];
CDS1.Open;
Caption := IntToStr(CDS1.RecordCount);
end;
procedure TForm1.CDS1AfterPost(DataSet: TDataSet);
begin
if CDS1.ApplyUpdates(0) = 0 then
CDS1.Refresh;
end;
procedure TForm1.CDS1AfterDelete(DataSet: TDataSet);
begin
CDS1.ApplyUpdates(-1);
end;
function TForm1.NextID: Integer;
begin
Dec(FID);
Result := FID;
end;
procedure TForm1.CDS1NewRecord(DataSet: TDataSet);
begin
CDS1.FieldByName('ID').AsInteger := NextID;
CDS1.FieldByName('IntValue').AsInteger := Random(100);
end;
procedure TForm1.CDS1AfterInsert(DataSet: TDataSet);
begin
CDS1.Post;
end;
procedure TForm1.CDS1CalcFields(DataSet: TDataSet);
begin
CDS1RowVerStr.AsString := GetRowVerString(CDS1RowVersion.Value);
end;
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