How to retrieve parent documents without a nested structure (block-join)

[Shamik Bandopadhyay]

Hi,

  I have a set of documents indexed which has a pseudo parent-child
relationship. Each child document has a reference to the parent document
through an ID. As the documents are not available to the crawler in order,
I'm not able to index them in a nested structure to support
block-join.Here's an example of a dataset in index right now.

<doc>
  <field name="id">1</field>
  <field name="title">Parent title</field>
  <field name="doc_id">123</field>
</doc>
<doc>
  <field name="id">2</field>
  <field name="title">Child title1</field>
  <field name="parent_doc_id">123</field>
</doc>
<doc>
  <field name="id">3</field>
  <field name="title">Child title2</field>
  <field name="parent_doc_id">123</field>
</doc>
<doc>
  <field name="id">4</field>
  <field name="title">Misc title2</field>
</doc>

As per my requirement, if I search on "title2", the result should bring
back the following result, the parent document (id=1) and non-related
document (id=4).

<doc>
  <field name="id">1</field>
  <field name="title">Parent title</field>
  <field name="doc_id">123</field>
</doc>
<doc>
  <field name="id">4</field>
  <field name="title">Misc title2</field>
</doc>

This is similar in lines with Block Join Parent Query Parser where I could
have fired a query like : q={!parent
which="content_type:parentDocument"}title:title2

Not sure if the Graph Query Parser can be a relevant solution in this
regard. The problem I see there is I'm running on 5.5 with 2 shard and n
number of replicas. The graph query parser seems to be designed for a
single node/single shard.

This is tad urgent for me as I'm trying to come up with an approach to deal
with this. Any pointers will be highly appreciated.

Thanks,
Shamik