Mega Code Archive
Make a virtual table [inmemory tables]
<![CDATA[
{
This is an InMemoryTable example. Free for anyone to use, modify and do
whatever else you wish.
Just like all things free it comes with no guarantees.
I cannot be responsible for any damage this code may cause.
Let me repeat this:
WARNING! THIS CODE IS PROVIDED AS IS WITH NO GUARANTEES OF ANY KIND!
USE THIS AT YOUR OWN RISK - YOU ARE THE ONLY PERSON RESPONSIBLE FOR
ANY DAMAGE THIS CODE MAY CAUSE - YOU HAVE BEEN WARNED!
THANKS to Steve Garland <72700.2407@compuserve.com> for his help.
He created his own variation of an in-memory table component and
I used it to get started.
InMemory tables are a feature of the Borland Database Engine (BDE).
InMemory tables are created in RAM and deleted when you close them.
They are much faster and are very useful when you need fast operations on
small tables. This example uses the DbiCreateInMemoryTable DBE function call.
This object should work just like a regular table, except InMemory
tables do not support certain features (like referntial integrity,
secondary indexes and BLOBs) and currently this code doesn't do anything to
prevent you from trying to use them. You will probably get some error if
you try to create a memo field.
}
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.
]]>