Joining with streaming expressions using hierarchical path

[Damiano Albani <da...@gmail.com>]

Hello,

I have documents in Solr which I'd like to join, based on properties
related to a hierarchical path.
Here's how it's basically structured:

{
>   path: "/books/book1",
>   ancestors: ["/", "/books"],
>   type: "book",
>   title: "Book #1"
> }
>
> {
>   path: "/books/book2",
>   ancestors: ["/", "/books"],
>   type: "book",
>   title: "Book #2"
> }
>

=====

{
>   path: "/books/book1/chapters/chapter1",
>   ancestors: ["/", "/books", "/books/book1", "/books/book1/chapters"],
>   type: "chapter",
>   number: 1,
>   title: "Chapter #1"
> }
>
> {
>   path: "/books/book1/chapters/chapter2",
>   ancestors: ["/", "/books", "/books/book1", "/books/book1/chapters"],
>   type: "chapter",
>   number: 2,
>   title: "Chapter #2"
> }
>
> {
>   path: "/books/book2/chapters/chapter1",
>   ancestors: ["/", "/books", "/books/book2", "/books/book2/chapters"],
>   type: "chapter",
>   number: 1,
>   title: "Chapter #1"
> }
>


Using streaming expressions, is there a way I could join those documents,
for example to find all books which have more than 1 chapter? Silly
example, but you get the idea :-)

At first, with the "ancestors" field as a TextField, using
*PathHierarchyTokenizerFactory* as index analyzer, I tried something like:

innerJoin(
>   search(
>     ... type:chapter where number > 1...
>   ),
>   search(
>     ... type:book ...
>   ),
>   on="ancestors=path")
>

Unfortunately, Solr complained that "ancestors must have DocValues to use
this feature".
I suppose this is related to https://issues.apache.org/jira/browse/SOLR-8362
.

So I thought, maybe should I turn "ancestors" into a multivalued *StrField*
??
But then the *FieldEqualitor* used for the join criteria doesn't seem to
work for "ancestors=path", given how the comparison is made.
Do I understand this correctly?

Anyway, I couldn't find many examples on how to use streaming expressions,
so I'm probably missing something obvious here.
Thanks for your help.

Regards,

-- 
Damiano Albani