I would be very interested to follow-up this subject closely,
as we are actually performing the same kind of work as you are looking for.
One of the answer you got was that it is not possible to reuse a prepared
statement from one database to another.
This answer was too quick, and did not include any explanation -> so I would
rather prefer to ask again the question, and obtain why it is not possible.
I would say that the test I have performed until now make this thing
possible.
I agree that this requires to tweak a little bit the way SQLite is working
(without recompiling anything, only using the internal members of the opaque
structures).
If VDBE programmers think that I am getting too deep inside the VDBE
internal structures to handle this problem, (or that it is too risky for
data integrity), please feel free to comment vigorously on this subject.
The work performed was to swap Database Handles.
Following code is included in XMLRAD DacSQLite3 to address exactly this
problem:
procedure StmtSwapVdbe(Statement: TDISQLite3StatementHandle; NewDB:
Pointer);
var
Vdbe: PVdbe;
begin
Vdbe := PVdbe(Statement);
if Vdbe.db = NewDB then
Exit;
// Uninstall Vdbe from its actual Vdbe.db
if Vdbe.pPrev <> nil then
Vdbe.pPrev.pNext := Vdbe.pNext
else
Vdbe.db.pVdbe := Vdbe.pNext;
if Vdbe.pNext <> nil then
Vdbe.pNext.pPrev := Vdbe.pPrev;
// Install Vdbe to the NewDB
Vdbe.db := NewDB;
if Vdbe.db.pVdbe <> nil then
Vdbe.db.pVdbe.pPrev := Vdbe;
Vdbe.pNext := Vdbe.db.pVdbe;
Vdbe.pPrev := nil;
Vdbe.db.pVdbe := Vdbe;
end;
Once again, if any programmer of the VDBE could comment on this, I am even
willing to pay money to get audit of the code, and get confirmation that
this technique is valid and does not put at risk data integrity of
databases.
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