We have lots of Query option in OData service. When I started learning SAP gateway I couldn’t get half of the queries, so thought of writing a blog explaining the most used queries in the odata service for the people who are trying to learn gateway and also for my future reference 
So first let us list the Query options in odata service that are often used and their uses.
Query Option | Description | Implementation Required |
$format | Return the response in particular format(JSON/XML/ATOM) without access to request headers for standard content-type negotiation. Example : https://<server>:<port>/.../<service_name>/Products?$format=json | No |
$count | Return the number of entries in the selection path. Example: https://<server>:<port>/.../<service_name>/Products?$count | No |
$Select | Return the entities listed in the value of the select query. Example: https://<server>:<port>/.../<service_name>/Products?$select=Category,Name | No |
$link | Returns the entities list for the navigation property specified in the link. Example: https://<server>:<port>/.../<service_name>/Products('1000')/$links/Category | No |
$expand | Returns the entities list for the navigation property specified by the value of expand. We can specify multiple navigation property separated by comma or ‘/’. Example : https://<server>:<port>/.../<service_name>/Suppliers?$expand=Category,Products | No |
$value | Return the raw value of a single entity without any formatting Example : https://<server>:<port>/.../<service_name>/Products('1000')/Name/$value | No |
$top | Return the response with N entries of the entity set specified in the URI. Used for client side Paging Example : https://<server>:<port>/.../<service_name>/Products?$top=5 | Yes |
$skip | Return the response skipping N entries of the entity set specified in the URI. Used for client side Paging Example : https://<server>:<port>/.../<service_name>/Products?$skip=5&$top=10 | Yes |
$filter | Return the subset of entries from collection of entries depending on the Boolean expression specified in the URI. Example: https://<server>:<port>/.../<service_name>/Products?$filter=Category eq 'Notebooks' | Yes |
$orderby | Return the entries ordered by the value specified in the URI. the sorting order asc/desc is specified in the URI. If not specified it will get sorted in ascending Example: https://<server>:<port>/.../<service_name>/Products?$orderby=Category desc | Yes |
$inlinecount | Return the number of entries in the collection of entries after applying all the filters specified in the URI. The inlinecount accepts two values ‘allpages’ and ‘none’. Example: https://<server>:<port>/.../<service_name>/Products?$inlinecount=allpages | Yes |
$skiptoken | Used for server side paging. The N entries specified in the URI would be returned from server side. The remaining entries would be returned on request. Example: https://<server>:<port>/.../<service_name>/Products?$skiptoken=20 | Yes |
Let us now see how to implement the Query options into our code. Whatever values we pass in the URI can be found in the import parameter “io_tech_request_context” of the method GET_ENTITYSET in the service implementation.
Implementation for $filter:
In the example below I have made the CARRID field as filterable field, so we can filter the result based on the CARRID in the odata query.
Implementation for $skip and $top:
Implementation for $orderby:
Implementation for $inlinecount:
