This blog is based on the idea of expanding Entities linked with Multi-Level Navigation Properties(A->B->C->D) in a single Gate Way framework call.
To get an idea of expanding multiple entities linked with Navigation property in a single ENTITYSET call with $EXPAND, refer to my recent blog at Expand Parent Child Entities in a Single Expansion – GET_EXPANDED_ENTITYSET.
Consider below entity relation ship ENTITY A -> ENTITY B-> ENTITY C linked with Navigation properties Entity A to Entity B = AB and Entity B to Entity C = BC. With this blog I am trying to fetch data for all the entities A, B and C in a single call of the gateway framework using below URI call where A is linked to B and B is linked to C via a navigation property. This is like an INNERJOIN on the interrelated Entities linked via navigation properties:
this would return data for entity A, B and C in a single Gateway Framework Call which would otherwise be achieved with below 2 Odata Calls:
In above entity expansion, you could always use filters based on the entities A and B, However, the way you access the various properties of entities A and B is slightly different.
Say you want to filter data result on the basis of property X of entity A, the above link would be represented as /sap/opu/odata/sap/zmultilevel_exp_srv/EntitySetA?$expand=AB/BC&$filter=X eq <Filter Value>.
However, if you want to filter result set based on property Y of entity B, the link would be represented as
/sap/opu/odata/sap/zmultilevel_exp_srv/EntitySetA?$expand=AB/BC&$filter=AB/Y eq <Filter Value>.
We will consider above situations with the help of Sales Order Data linked with entity relations SalesOrder Header -> Sales Order Items ->Sales Order Schedule Lines
Consider below Entity Structures and Navigation Properties:
Redefine GET_EXPANDED_ENTITYSET as explained in the attached snapshot.
The catch here is that, we have to tell the GW framework that we have expanded the Header, Item and Schedule Line entities in a single entity set call and no need to call the child entity set to fetch the the Sales Order Items and Sales Order Schedule Lines. We can do this using parameter ET_EXPANDED_TECH_CLAUSES of GET_EXPANDED_ENTITYSET. Append both the Navigation Property Name(SOHEADERTOITEM/SOITEMTOSCHDLN) in this exporting parameter, which will tell the gate way framework that the child entity has already been expanded and there is no need to call the child entity sets.
An important point to not here is that the structure of the output entity set should have fields with Name same as Navigation Property Name(SOHEADERTOITEM and SOITEMTOSCHDLN). Check structure below.
Access Scheduel lines data along with Header and Line Items:
With filter on base entity(SOHeader)
With filter on Items Entity (SOItem): The catch here is that, you have to fetch the filter from the filter string from IO_TECH_REQUEST_CONTEXT->MO_FILTER->MV_FILTER_STRING.
Kindly share your inputs and thoughts on this.