How to enable solr document cache between 2 independent entities? - caching

Question

Am trying to index an application (which has both metadata and attachments along with it). Am using DIH to build the solr documents. In my DIH Config xml, i have defined 2 separate entities, in which first one will fetch the metadata for all my active records, and the second entity will fetch the attachments(can be 0 to many )for all those records.
Both these entities have a "SEQUENCE ID" in common, Is there a way i can cache the SEQUENCE IDs from my first entity & re use that in second entity?
Appreciate any help
Thanks!
<entity name="metadata" query="SELECT sequence_id,field1,field2 from table1 where active_indicator='Y'">
<field column="sequence_id" name="seq_id"/>
<field column="field1" name="field_1"/>
<field column="field2" name="field_2" />
</entity>
<entity name="attachments" query="select t2.sequence_id,t2.field3 from table1 t1,table2 t2 where t1.sequence_id=t2.sequence_id and t1.sequence_id=(SELECT sequence_id from table1 where active_indicator='Y')">
<!--if i can get the t1.sequence_id cached, i can use them to select attachments for those seq ids alone-->
<field column="sequence_id" name="seq_id"/>
<field column="field3" name="field_3"/>
</entity>
</document>

Answer 1

You can wrap your dependent entities inside the entity it depends on, which will give you access to the column values for the rows in the parent entity. There's an example in the community wiki with multiple entities within each other.
<entity name="record" query="SELECT * FROM records">
<entity name="attachment"
query="SELECT field_1, field_2 FROM attachments WHERE SEQUENCE_ID='${record.SEQUENCE_ID}'">
<field name="attachment_val" column="field_1" />
</entity>
<field ... />
</entity>
This is the basic DIH configuration and should work. To rewrite this to use the cache implementation (if that's what you're asking for), you'll have to configure the inner entity to select all rows and use the cache for lookups:
<entity name="attachment"
query="SELECT field_1, field_2 FROM attachments"
cacheKey="SEQUENCE_ID" cacheLookup="record.SEQUENCE_ID">
....
</entity>
The functionality should otherwise be the same.