Topic: Checking for database resident entities

[MickD]

Below is some code snippes I'm working with, it's for the python arx wrappers I'm working on and unless I sort this out in the best possible fashion it will be the weak link in the chain!

When passing pointers back and forth with Python, you wrap your pointer in a CPyObject (basically a container for a void*) in this fashion -

Code: [Select]

// create the new line to pass back to python:
AcGePoint3d *p1 = new AcGePoint3d(x1, y1, z1);
AcGePoint3d *p2 = new AcGePoint3d(x2, y2, z2);
AcDbLine* newline = new AcDbLine(*p1, *p2);
return PyCObject_FromVoidPtr(newline, del_ent);
where 'del_ent' is a function ptr to a delete function for cleanup.
With that, Python has a pointer to the new db entity and can do what it needs to do with it, however, once you return back to the host app Python needs to do its cleanup, this is what I have so far, it works but I'm not happy with it -

Code: [Select]

static void del_ent(void* ptr)
{
/* just return and python will be happy, again, we need
to be careful with this as we could easily create a memory leak! */
AcDbEntity* e = (AcDbEntity*)ptr;
//e->upgradeOpen();
if(e->blockId() == AcDbObjectId::kNull) // it's not a db resident, we can delete it.
delete ptr;
//e->close();
return;
}
the problem is the doc's say you're not supposed to 'access' the pointer if it's not open, would using e->BlockId() without the entity being open be breaking the rules?? (it seems to work...)
Is there a better way to check if an entity/object belongs to a db without opening it?

thanks.
Mick.

[It's Alive!]

It seems as long as you are not modifying anything, It should be ok to check the ObjectID for isNull or isValid

Code: [Select]

if(e->objectId().isNull()) // it's not a db resident, we can delete it.
      delete ptr;


[MickD]

Thanks Dan.

I was thinking about this also, it may be safer just to pass ObjectId's back and forth instead...if I deleted one of those I may well have the same problem though(?).

[MickD]

Nope, ObjectId is probably the same if not worse!

I'll experiment with handles for a bit, it also avoids passing pointers about but will make for a bit of work dealing with the entities (opening etc).

[T.Willey]

Just a guess....  If the entity is not a db resident, will it not have an OwnerId then?  ..../guess

[pkohut]

I think your fine Mick, maybe change like so?  Being unsure about implementation
details I don't know if you need to close the object here or somewhere else.

Code: [Select]

static void del_ent(void* ptr)
{
    /* just return and python will be happy, again, we need
    to be careful with this as we could easily create a memory leak! */
    AcDbObject* pObj = AcDbObject::cast(ptr);
    if(pObj)
    {
        if(pObj->blockId() == AcDbObjectId::kNull) // it's not a db resident, we can delete it.
            delete pObj;
        else
            pObj->close();
    }
}

Paul

[MickD]

Thanks Paul, yes, closing is another issue but it won't hurt to close it anyway as the object would be open at creation and I would be opening to edit objects anyway, python will call this method once it loses focus so it's sort of a safety net I guess.

I don't want the python interface to mimic arx too much, it would make it too verbose and would defeat the purpose of using python I think, I'd rather it be more like vb which handles the db interaction behind the scenes so you can just concentrate on the scripting.
cheers,
Mick.