Re: [sqlite] How to create connection life-time object?

[Dušan Paulovič]

What I need is 'install and don't care' because I use many C++ classes
as lifetime objects.
I think that my solution does work now well, but if there would be a way to
avoid use of SQL parser, it would be better.


2013/7/27 Max Vlasov 

> On Fri, Jul 26, 2013 at 9:56 PM, Dušan Paulovič 
> wrote:
>
> > Thanks for suggestion, but:
> > 1.) one object is not linked to one connection
> >
>
> If you have your own memory management, it's not a problem since the scheme
> I described is basically just a storage of pointers. To free or not to free
> (if the pointer points to a disposable entity) is your decision at your
> chosen time. But if you want automatic reference counting (so when a
> pointer not referenced anymore, it would be automatically deallocated),  I
> agree, the proposal is not good. Probably using your own global structure
> not related to sqlite is less pain.
>
>
> > 2.) object is not destroyed together with connection
> >
>
> The same, you're free to use the table just as pointers storage
>
> Max
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Re: [sqlite] How to create connection life-time object?

[Max Vlasov]

On Fri, Jul 26, 2013 at 9:56 PM, Dušan Paulovič  wrote:

> Thanks for suggestion, but:
> 1.) one object is not linked to one connection
>

If you have your own memory management, it's not a problem since the scheme
I described is basically just a storage of pointers. To free or not to free
(if the pointer points to a disposable entity) is your decision at your
chosen time. But if you want automatic reference counting (so when a
pointer not referenced anymore, it would be automatically deallocated),  I
agree, the proposal is not good. Probably using your own global structure
not related to sqlite is less pain.


> 2.) object is not destroyed together with connection
>

The same, you're free to use the table just as pointers storage

Max
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Re: [sqlite] How to create connection life-time object?

[Dušan Paulovič]

Thanks for suggestion, but:
1.) one object is not linked to one connection
2.) object is not destroyed together with connection

Dusan


2013/7/26 Max Vlasov 

> Hi, Dušan
>
>
> On Thu, Jul 25, 2013 at 2:39 PM, Dušan Paulovič 
> wrote:
>
> > Hello, is there a way to somehow set a connection life-time object?
> > ...
> >
> >
> > It would be fine to have something like:
> > int sqlite3_set_lifetime_object(
> >   sqlite3 *db,  /*db connection*/
> >   const char *zObjectName,  /*utf8 name of object*/
> >   void *pObject,/*if NULL, object is removed*/
> >   void(*xDestroy)(void*)/*destructor*/
> > );
> >
> > void * sqlite3_get_lifetime_object(
> >   sqlite3 *db,  /*db connection*/
> >   const char *zObjectName   /*utf8 name of object*/
> > );
> >
>
>
>
> How about temporary memory table just for the task of storing your objects.
>
> You initialization code for particular connection
>   Attach ':memory:' as MyObjectStorage
>   Create table MyObjectStorage.[objects] (Name Text, Ptr Text)
>
> Your code for inserting an object
>   Insert into MyObjectStorage.[objects] (Name, Ptr) VALUES ('obj1',
> '0x12345678')
>
> This code will query the pointer
>   select Ptr from MyObjectStorage.[objects] where Name='obj1'
>
> The only convention rule here will be the name of the attached db so no
> other databases (or instances of the same storage) should use this name.
>
> Max
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Re: [sqlite] How to create connection life-time object?

[Max Vlasov]

Hi, Dušan


On Thu, Jul 25, 2013 at 2:39 PM, Dušan Paulovič  wrote:

> Hello, is there a way to somehow set a connection life-time object?
> ...
>
>
> It would be fine to have something like:
> int sqlite3_set_lifetime_object(
>   sqlite3 *db,  /*db connection*/
>   const char *zObjectName,  /*utf8 name of object*/
>   void *pObject,/*if NULL, object is removed*/
>   void(*xDestroy)(void*)/*destructor*/
> );
>
> void * sqlite3_get_lifetime_object(
>   sqlite3 *db,  /*db connection*/
>   const char *zObjectName   /*utf8 name of object*/
> );
>



How about temporary memory table just for the task of storing your objects.

You initialization code for particular connection
  Attach ':memory:' as MyObjectStorage
  Create table MyObjectStorage.[objects] (Name Text, Ptr Text)

Your code for inserting an object
  Insert into MyObjectStorage.[objects] (Name, Ptr) VALUES ('obj1',
'0x12345678')

This code will query the pointer
  select Ptr from MyObjectStorage.[objects] where Name='obj1'

The only convention rule here will be the name of the attached db so no
other databases (or instances of the same storage) should use this name.

Max
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[sqlite] How to create connection life-time object?

[Dušan Paulovič]

Hello, is there a way to somehow set a connection life-time object?

I mean something like:
Let's imagine you are working with some sqlite3 connection and want so
share same data with extensions, but must be guaranteed, that object gets
destroyed when connection is closed.

For now, I use creating function mechanism for it:
(pseudo - not tested code)
void return_user_data(sqlite3_context* ctxP, int argc, sqlite3_value** argv)
{
  void * ptr = sqlite3_user_data(ctxP);
  sqlite3_result_blob(ctxP, (void*), sizeof(void*));
}

int register_app_obj(sqlite3 * db)
{
  my_type *m_obj = (my_type*) sqlite3_malloc(sizeof(my_type));
  if (m_obj &&
SQLITE_OK != sqlite3_create_function_v2(
db, "app_obj", 0, SQLITE_ANY, m_obj,
return_user_data, NULL, NULL, sqlite3_free))
  {
sqlite3_free(m_obj);
m_obj = NULL;
return SQLITE_ERROR;
  }
  return SQLITE_OK;
}

Then if extension needs to get app_obj it queries "SELECT app_obj();" and
translates blob.
But this way it is too much of overhead and also there is a restriction,
that functions
can be registered only if there is no any active statement.

I have also made a complicated virtual table implementation of the same,
because
modules can be registered while statements are active, but it is much more
complicated
then such thing should be.

Do you have any idea?

It would be fine to have something like:
int sqlite3_set_lifetime_object(
  sqlite3 *db,  /*db connection*/
  const char *zObjectName,  /*utf8 name of object*/
  void *pObject,/*if NULL, object is removed*/
  void(*xDestroy)(void*)/*destructor*/
);

void * sqlite3_get_lifetime_object(
  sqlite3 *db,  /*db connection*/
  const char *zObjectName   /*utf8 name of object*/
);
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