将参数传递给ASP.NET的Web API 2 OData v4 REST API

Question

Microsoft's OData implementation lets filtering a dataset by applying a boolean expression in the $filter option. This serves well for dynamic filtering (usually requested by the client), but what if the REST API's GET method for enumerating a list needs some base input parameters that are always required?

For example, let's define the following models on our Web API controller:

public class RoastedCoffeeProduct
{
    [Key]
    public Guid ProductId { get; set; }
    public string Name { get; set; }
    public string Brand { get; set; }
    public string StoreName { get; set; }
    public Location StoreLocation { get; set; }
    public decimal CurrentPrice { get; set; }
    public int StoreStock { get; set; }
}

public class Location
{
    public Guid LocationId { get; set; }
    public string Country { get; set; }
    public string Region { get; set; }
}

and then define the following GET method on the REST API:

/odata/RoastedCoffeeProducts/

The expectation is to get an enumeration of all roasted coffee products available for sale in the stores of a given location. A use case would be the following: "Get all roasted coffee products for sale on location Country: 'US', Region: 'Redmond'". This should return an enumeration of many JSON items like the one below (only one is shown for brevity):

{
   "ProductId": "D6B543AE-D6A6-42C2-A4B1-70402B4B2AD1",
   "Name": "Iperespresso capsules",
   "Brand": "Illy",
   "StoreName": "5 Stones Coffee Company",
   "StoreLocation": { "LocationId": "0AB30128-0EF1-4B8C-9EC6-DCF0F27BB828", "Country": "US", "Region": "Redmond" },
   "CurrentPrice": "15.90",
   "StoreStock": "4"
}

So let's assume that the required base input parameters for the GET method are "Country" and "Region". They always should be provided, because the Web API 2 Controller calls the following method for fetching them:

var productsBeingSold = storesRepository.FindAllCoffeeProducts(country, region);

So, the FindAllCoffeeProducts method in the repository needs the country and region as input parameters. Let's assume this method returns about 200 items. If the client wants to further filter this 200 items dataset, like, those whose product name is "Nespresso capsules", then OData filtering capabilities enter in action:

/odata/RoastedCoffeeProducts?$filter=name eq 'Nespresso capsules'

That way OData will automatically filter all matching items from the 200 items dataset. My question is about the required base input parameters Country and Region: should they be provided in the OData $filter clause as well? I think this is not correct, because strictly speaking is not part of the filter, but part of the input parameters needed to work properly. Where should they be provided then? In the body maybe? OData filtering should be applied to the resulting dataset, but the dataset needs to know the Country and Region as required input parameters.

Answer 1

What you are describing is an OData Function, this can take certain parameters and the results can still be filtered and sorted etc. For more details see this link: https://docs.microsoft.com/en-us/aspnet/web-api/overview/odata-support-in-aspnet-web-api/odata-v4/odata-actions-and-functions

Here is an example of an unbound function using the OData TripPin example service that has a function called GetNearestAirport that takes 2 parameters, lat and lon that have been specified in the URL: http://services.odata.org/V4/TripPinServiceRW/GetNearestAirport(lat=0,lon=0)