Projection

Projection allows a REST API client to control:

Which properties of the queried resource should be returned (omit the rest).
Which related objects should be expanded beyond their key property to expose more values.

This is accomplished using the $select and $expand query options.
- By default, no relations are expanded.
- They can be combined to fine-tune which fields and related entities are returned.

Examples

1. Return all properties of a single Service Request

GET http://myserver:5181/odata/ServiceRequests(3101097999)

2. Return only specific fields (Description, Information)

GET http://myserver:5181/odata/ServiceRequests(3101097999)?$select=Description,Information

3. Return fields plus expand related Workorders (all fields)

GET http://myserver:5181/odata/ServiceRequests(3101097999)?$select=Description,Information&$expand=Workorders

4. Return fields plus expand related Workorders (selected fields only)

GET http://myserver:5181/odata/ServiceRequests(3101097999)?$select=Description,Information&$expand=Workorders($select=ID,Description)

5. Expand Workorders for the first 10 Service Requests

GET http://myserver:5181/odata/ServiceRequests?$top=10&$select=Description,Information&$expand=Workorders($select=ID,Description)

6. Expand a Caller (1:1 or N:1 relation)

GET http://myserver:5181/odata/ServiceRequests(3101097999)?$expand=Caller

7. Expand Caller and its Organization (selected fields)

GET http://myserver:5181/odata/ServiceRequests(3101097999)?$select=Description,Information&$expand=Caller($expand=Organization($select=Name))

If the $select clause is omitted for Organization, all its fields will be returned.

Invalid Usage

Navigation properties must not be included in $select.
The following are invalid:

http://myserver:5181/odata/ServiceRequests(3101097999)?$select=Uid,Description,Information,Workorders
http://myserver:5181/odata/ServiceRequests(3101097999)?$select=Uid,Description,Information,Caller

Correct usage with $expand:

http://myserver:5181/odata/ServiceRequests(3101097999)?$select=Uid,Description,Information&$expand=Workorders
http://myserver:5181/odata/ServiceRequests(3101097999)?$select=Uid,Description,Information&$expand=Caller

Important Note on `$select` with `$expand`

When expanding a navigation property while using $select, the Uid key property must be included.

Invalid:

http://myserver:5181/odata/ServiceRequests(3101097999)?$select=Description,Information&$expand=Caller

Valid:

http://myserver:5181/odata/ServiceRequests(3101097999)?$select=Uid,Description,Information&$expand=Caller