Hi Experts,
I was trying to create a Analytical List Report Application consuming an OData service. From the Analytical List report Fiori element documentation I got to know this type of application only works for analytical(?) and the OData service should have some specific annotations like - "aggregate" and "sap:aggregation-role=dimension/measure".

For experiment, I created a service(I'm on 7.4 SP012 on HDB) with only SPFLI structure and created a mapping from DDIC source SPFLI. I generated the SEGW project.

Then I also annotated my Entity and properties with "aggregate" and dimension/measure through MPC_EXT(redefining DEFINE method). I added "Generated_ID" as a key because I read from a blog that aggregations do not work without a generic key like that.

After all these, my metadata looks like below -

I also added the aggregation logic for the "FlightTimeSum" field on the dpc_ext IF_SADL_GW_QUERY_CONTROL~SET_QUERY_OPTIONS.
* Set the aggregation fields.
* Provide the measure to be aggregated as ‘element’ and the ABAP field name of the property that contains
* the result of the aggregation as ‘alias’.
io_query_options->set_aggregation( VALUE #( ( element = 'FLIGHTTIMESUM' alias = 'FLTIME'
type = if_sadl_gw_query_options=>co_aggregation_type-sum )
) ).
Now, when I run the get query I get the following results but no "Generated_ID" populated.

In another discussion segment of a blog from Joseph Berthe, https://blogs.sap.com/2018/01/12/fiori-elements-analytical-table-with-sadl/ I got to know the SAP given sources are okay to use as source mapping.
When I consume this service through FIORI I get lot of duplicated entries. I guess because the entity was having only one key "generated_id" which remained blank, caused the duplicities. No luck when tried to implement charts as well.
Now, I have three questions -
1. How can we populate the "GENERATED_ID"? With a correct design, this should be auto populated I believe. Am I missing any major part here?
2. Even if I somehow populate the generated_id and create a CUBE type of data model(one showed in this blog - https://blogs.sap.com/2018/03/18/create-an-analytical-model-based-on-abap-cds-views/ ) will I be able to do the aggregate function and render the charts like CDS Analytical views? (I'm asking this because when I created a CDS and tried to add "@Analytics" annotation it refused to take that, because of my version. It allows me to add @Analytics in 7.5 system.)
3. Is there any way around to develop a custom gateway service which will allow me to create an Analytical List Report? My actual business scenario demands a custom implementation.
Any leads regarding any of these questions will be appreciated. Am I messing up with SADL and Analytical concepts?