Traverse command: how to use $current context variable

[Riccardo Tasso]

Hi, I am trying to understand the potential of TRAVERSE command ( http://orientdb.com/docs/2.1/SQL-Traverse.html ).

The documented examples, which all use the $depth context variable are clear.

I can't figure out how to use other variables, first of all $current.

Consider this toy-dataset:

create database memory:tmp admin admin

insert into V set name = 'root'

insert into V set name = '1'   

insert into V set name = '2'

insert into V set name = '1.1'

insert into V set name = '1.2'

insert into V set name = '2.1'

insert into V set name = '2.2'

insert into V set name = '2.3'

create edge from #9:0 to #9:1

create edge from #9:0 to #9:2

create edge from #9:1 to #9:3

create edge from #9:1 to #9:4

I would expect to find something with those query, but no result is returned:

TRAVERSE out() FROM (SELECT FROM V WHERE name = 'root') WHILE name = '2.3'
TRAVERSE out() FROM (SELECT FROM V WHERE name = 'root') WHILE $current.name = '2.3'

Is there any possibility to stop the TRAVERSE with some condition on the current vertex?

Thanks,

   Riccardo

[Luigi Dell'Aquila]

Hi Riccardo,

your root node name is 'root', so it does not match your traversal condition ;-)

Try with this:

TRAVERSE out() FROM (SELECT FROM V WHERE name = 'root') WHILE name = '2.3' or $depth = 0

I hope I understood correctly your problem... the result will be the following:

suppose you have this chain:

A:'root' -> B:'2.3' -> C:'2.3' -> D:'something else'

you will obtain

A

B

C

Luigi

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[Riccardo Tasso]

Yeah, you right: now I see the point!

Cheers,

   Riccardo

[François Charette]

Riccardo,

Maybe you had in mind something like this:

TRAVERSE out() FROM #9:0 UNTIL name ='2.3'

where the hypothetical command UNTIL would mean "continue the traversal until some condition is met, and then stop" (including the vertices that match the UNTIL condition) ?

For some use cases this would greatly simplify traversal operations I think, especially when the depth of the end-points cannot be known in advance.

Cheers
François

[Luigi Dell'Aquila]

Hi guys, 

UNTIL can be expressed as a negative WHILE, in this case 

TRAVERSE out() FROM #9:0 UNTIL name ='2.3'

is the same as

 

TRAVERSE out() FROM #9:0 WHILE name <> '2.3'

so there is no strict reason to have this.

I also suggest you to take a look at the roadmap for 2.2, we will support a new query paradigm, that is pattern matching. Here you can find some info https://github.com/orientechnologies/orientdb-docs/blob/master/SQL-Match.md

With MATCH statement you will have much finer control on traversal, using WHERE and WHILE together

Luigi