When you have an OData API-layer on top of your Mendix database, you can work with the following options documented by Mendix: https://docs.mendix.com/refguide/odata-query-options/
Specifically for the $expand-option in the URL to navigate to an associated entity, Mendix supports up to the following URL’s:
Associated objects can be retrieved by passing the
$expand query parameter. For example:
/odata/myservice/v1/Employees?$expand=Cars,Address($expand=City) (OData 4) or
/odata/myservice/v1/Employees?$expand=Cars,Address/City (OData 3).
In the above example, I will get the Employee-entity with all of its attributes, the associated Car-entity with all of its attributes, the associated Address-entity and all of its attributes, together with the associated City-entity and all of its attributes.
However, I want to have the flexibility to only select the attribute(s) of the associated entity/entities that I need. Not all of them. Which would result in the following (according to official OData.org documentation):
/odata/myservice/v1/Employees?$expand=Cars($select=BrandName),Address($expand=City($select=ZipCode)) (OData v4)
In this example, I’d like to have the Employee-entities with a column for their car’s brandname and the zipcode of their city. Basically, just two columns instead of everything of the car- and city-attributes.
I would advise to have the same option for OData v3.