V4RB2 vLink

[Ruslan Zasukhin]

On 11/22/04 10:32 PM, "erne" <ernestogiannotta at tiscalinet.it> wrote:

> What the BranchCount property indicates? Can it be more than 2?

In Valentina 2.0 it is always 2.

Yes in future we plan add support of N-branch links.
Just I do not see yet full picture.


Please download new V4RBRef.pdf
It now have description of 2 more classes

    Vlink
        + ---- VLink2
                 +------ VBinaryLink

So Vlink is general kind link. Can be N-link.

Link2 adds more properties and methods for Link with 2 branches.
Note that today we have 3 links of link2
    ObjectPtr
    ForeignKey
    BinaryLink

So we always must be able CAST TO Link2 any of this 3 classes,
And work with it on general abstraction of link-2

> Why the Owner must be one of the linked tables? Can't vLink live at DB
> level?

Erne, please note that Links are on the db level.
You ask DB to create or drop link.

Owner here have sense of CASCADE deletion.
If you delete record of owner then child records can be deleted.

> What exactly Temporary means? The link will be deleted on DB.Close?

The same as for table. Temporary Table or link.
It is stored in the .tmp volume.

> and finally, how can vLink be used via SQL?

> Thanks for listening
> (and, of course, for all these new supercool features :-)

Please look at our SQL grammar.
Link is on the same page where you download V4RB 2.0

By memory, we have

    CREATE LINK
    DROP LINK
    INSERT INTO LINK
    
We have extend the syntax of SQL92 join to use Link instead of fields

SQL92

       FROM T1 join T2 on T1.id = T2.ptr

Valentina also can do
    
      FROM T1 join T2 on LinkName
 

-- 
Best regards,
Ruslan Zasukhin      [ I feel the need...the need for speed ]
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e-mail: ruslan at paradigmasoft.com
web: http://www.paradigmasoft.com

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