Как создать таблицу в памяти?

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Code:

{

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.

 

 

©Drkb::02593

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