根據DELTA自動生成SQL語句
上傳客戶端的CLIENTDATASET.delta到伺服器的clientdataset.data，服務端解析clientdataset的資料生成相應的SQL語句。
相對於直接呼叫datasetprovider.applyupdates()方法提交資料而言，前者的可控性更強，對於某些要求靈活性很強的場合，前者可能是必須的提交方式。
procedure TBaseService.ApplyUpdates(const Delta: OleVariant; TableName, KeyField: WideString);
var
Flag: Boolean;
begin
if VarIsNull(Delta) then exit;
with (FParent as TDataServer2) do
begin
cdsDelta.Close;
cdsDelta.Data := Delta;
Flag := cdsDelta.FindField('SYS_STATUS') <> nil;
end; // with
if Flag then
InnerApplyUpdates2(TableName, KeyField)
else
InnerApplyUpdates(TableName, KeyField);
end;
function vartosql(value: Variant): wideString;
var
tmp:widestring;
begin
if (varisnull(Value)) or (varisempty(Value)) then
Result:='NULL'
else
case Vartype(value) of
varDate:
begin
tmp := formatDatetime('yyyy-mm-dd hh:mm:ss', VartoDatetime(Value));
Result:=Quotedstr(tmp);
end;
varString,varOlestr:
Result:=Quotedstr(Trim(Vartostr(Value)));
varboolean:
begin
if Value then
Result:='1'
else
Result:='0';
end;
varSmallint,varInteger,varDouble,varShortInt,varInt64,varLongWord,varCurrency:
begin
Result:=trim(Vartostr(Value));
end;
else
Result:=Quotedstr(Trim(Vartostr(Value)));
end;
end;
procedure TBaseService.InnerApplyUpdates(TableName, KeyField: WideString);
var
i: integer;
s1, s2: string;
CmdStr: string;
FieldList: TStringList;
begin
with (FParent as TDataServer2) do
begin
FieldList := TStringList.Create;
Connection.GetFieldNames(TableName, FieldList);
if not cdsDelta.Active then cdsDelta.Open;
for i := 1 to FieldList.Count do
if cdsDelta.FindField(FieldList[i - 1]) <> nil then
cdsDelta.FindField(FieldList[i - 1]).Tag := 1;
FieldList.Free;
if cdsDelta.RecordCount > 0 then
begin
cdsDelta.First;
s1 := '';
s2 := '';
while not cdsDelta.Eof do
begin
CmdStr := '';
case cdsDelta.UpdateStatus of
usUnmodified:
begin
s2 := VarToSql(cdsDelta[KeyField]);
end;
usModified:
begin
s1 := '';
for i := 1 to cdsDelta.FieldCount do
// if (not cdsDelta.Fields[i - 1].IsNull) and (cdsDelta.Fields[i - 1].Tag = 1) then
if (cdsDelta.Fields[i-1].NewValue <> System.Variants.Unassigned and (cdsDelta.Fields[i - 1].Tag = 1) then
begin
if s1 = '' then
s1 := Trim(cdsDelta.Fields[i - 1].FieldName) + ' = ' + VarToSql(cdsDelta.Fields[i - 1].Value)
else
s1 := s1 + ',' + Trim(cdsDelta.Fields[i - 1].FieldName) + ' = ' + VarToSql(cdsDelta.Fields[i - 1].Value);
end;
if s1 <> '' then
begin
CmdStr := 'Update ' + TableName + ' Set ' + s1 + ' Where ' + KeyField + ' = ' + s2;
end;
end;
usInserted:
begin
s1 := '';
s2 := '';
for i := 1 to cdsDelta.FieldCount do
if (not cdsDelta.Fields[i - 1].IsNull) and (cdsDelta.Fields[i - 1].Tag = 1) then
begin
if s1 = '' then
begin
s1 := Trim(cdsDelta.Fields[i - 1].FieldName);
s2 := VarToSql(cdsDelta.Fields[i - 1].Value);
end
else
begin
s1 := s1 + ',' + Trim(cdsDelta.Fields[i - 1].FieldName);
s2 := s2 + ',' + VarToSql(cdsDelta.Fields[i - 1].Value);
end;
end;
if s1 <> '' then
begin
CmdStr := 'Insert into ' + TableName + '(' + s1 + ') Values (' + s2 + ')';
end;
end;
usDeleted:
begin
s2 := VarToSql(cdsDelta[KeyField]);
CmdStr := 'Delete ' + TableName + ' Where ' + KeyField + ' = ' + s2;
end;
end;
if CmdStr <> '' then Cmd.Execute(CmdStr);
cdsDelta.Next;
end;
cdsDelta.First;
cdsDelta.EmptyDataSet;
cdsDelta.Close;
end;
end;
end;