Title: How to make a virtual table (InMemory tables)
unit Inmem;
interface
uses DBTables, WinTypes, WinProcs, DBITypes, DBIProcs, DB, SysUtils;
type
TInMemoryTable = class(TTable)
private
hCursor: hDBICur;
procedure EncodeFieldDesc(var FieldDesc: FLDDesc;
const Name: string; DataType: TFieldType; Size: Word);
function CreateHandle: HDBICur; override;
public
procedure CreateTable;
end;
implementation
{
Luckely this function is virtual - so I could override it. In the
original VCL code for TTable this function actually opens the table -
but since we already have the handle to the table - we just return it
}
function TInMemoryTable.CreateHandle;
begin
Result := hCursor;
end;
{
This function is cut-and-pasted from the VCL source code. I had to do
this because it is declared private in the TTable component so I had no
access to it from here.
}
procedure TInMemoryTable.EncodeFieldDesc(var FieldDesc: FLDDesc;
const Name: string; DataType: TFieldType; Size: Word);
const
TypeMap: array[TFieldType] of Byte = (fldUNKNOWN, fldZSTRING, fldINT16,
fldINT32, fldUINT16, fldBOOL,
fldFLOAT, fldFLOAT, fldBCD, fldDATE, fldTIME, fldTIMESTAMP, fldBYTES,
fldVARBYTES, fldBLOB, fldBLOB, fldBLOB);
begin
with FieldDesc do
begin
AnsiToNative(Locale, Name, szName, SizeOf(szName) - 1);
iFldType := TypeMap[DataType];
case DataType of
ftString, ftBytes, ftVarBytes, ftBlob, ftMemo, ftGraphic:
iUnits1 := Size;
ftBCD:
begin
iUnits1 := 32;
iUnits2 := Size;
end;
end;
case DataType of
ftCurrency:
iSubType := fldstMONEY;
ftBlob:
iSubType := fldstBINARY;
ftMemo:
iSubType := fldstMEMO;
ftGraphic:
iSubType := fldstGRAPHIC;
end;
end;
end;
{
This is where all the fun happens. I copied this function from the VCL
source and then changed it to use DbiCreateInMemoryTable instead of
DbiCreateTable.
Since InMemory tables do not support Indexes - I took all of the
index-related things out
}
procedure TInMemoryTable.CreateTable;
var
I: Integer;
pFieldDesc: pFLDDesc;
szTblName: DBITBLNAME;
iFields: Word;
Dogs: pfldDesc;
begin
CheckInactive;
if FieldDefs.Count = 0 then
for I := 0 to FieldCount - 1 do
with Fields[I] do
if not Calculated then
FieldDefs.Add(FieldName, DataType, Size, Required);
pFieldDesc := nil;
SetDBFlag(dbfTable, True);
try
AnsiToNative(Locale, TableName, szTblName, SizeOf(szTblName) - 1);
iFields := FieldDefs.Count;
pFieldDesc := AllocMem(iFields * SizeOf(FLDDesc));
for I := 0 to FieldDefs.Count - 1 do
with FieldDefs[I] do
begin
EncodeFieldDesc(PFieldDescList(pFieldDesc)^[I], Name,
DataType, Size);
end;
{ the driver type is nil = logical fields }
Check(DbiTranslateRecordStructure(nil, iFields, pFieldDesc,
nil, nil, pFieldDesc));
{ here we go - this is where hCursor gets its value }
Check(DbiCreateInMemTable(DBHandle, szTblName, iFields, pFieldDesc, hCursor));
finally
if pFieldDesc nil then FreeMem(pFieldDesc, iFields * SizeOf(FLDDesc));
SetDBFlag(dbfTable, False);
end;
end;
end.