If two tables are used for N:N relationship, an auto-generated intersect table is used to store the relational data. This intersect table is not exposed to table permissions. Without this feature, N:N relationship is not useful at all, as the relational data is not exposed. This same data is exposed over CRM APIs using $expand keyword, but is missing from oData APIs.
These auto-generated intersect tables should be available over oData as well, to allow feature parity with CRM APIs.
Thanks Jitendra for logging this idea. I am adding few more details with screenshots so that it would be easier to relate the differences in terms of querying entity relationship data over API from CRM and Portals.
An N:N relationship was created which then created a relationship entity --> new_passengercarriers
Created sample records on these two new entities and then associated some records.
When one queries over the DB for the contents under this table, we can see that it includes only a few columns relevant to the two entities record associations.
This whole relationship table data can be queried over the CRM web API by suffixing “Set” within the logical name of the relationship entity.
Example Relationship Entity name :: new_passengercarriers