Creating valid odata output for aggregation using dynamic EDM model

[mjordan73]

Hi. We have a service that currently utilises the Dynamic EDM Model approach. I've been asked to look into adding support for some aggregation functionality (basic $apply groupby and aggregate sum & count). I've been able to integrate mapping the odata request and the requested aggregation onto our other back end service that the odata endpoint uses as its datasource OK. Where i've hit a problem is with then creating an EDMEntityObjectCollection (based on approach of the DynamicEdmModelCreation sample project) that generates what I believe to be a valid odata response.

To illustrate the issue i'm going to take the example for groupby from the oasis docs http://docs.oasis-open.org/odata/odata-data-aggregation-ext/v4.0/cs01/odata-data-aggregation-ext-v4.0-cs01.html#_Toc378326304

In their case then the request GET ~/Sales?$apply=groupby((Customer/Country,Product/Name), aggregate(Amount with sum as Total)) would return

{
  "@odata.context": "$metadata#Sales(Customer(Country),Product(Name),Total)",

  "value": [
    { "@odata.id": null, "Customer": { "Country" : "Netherlands" },
      "Product": { "Name": "Paper" }, "Total": 3 },
    { "@odata.id": null, "Customer": { "Country": "Netherlands" },
      "Product": { "Name": "Sugar" }, "Total": 2},
    { "@odata.id": null, "Customer": { "Country: "USA" },
      "Product": { "Name": "Coffee" }, "Total": 12},
    { "@odata.id": null, "Customer": { "Country: "USA" },
      "Product": { "Name": "Paper" },"Total": 5},
    { "@odata.id": null, "Customer": { "Country: "USA" },
      "Product": { "Name": "Sugar" }, "Total": 2}
  ]
}

Although its proved difficult to find a definitive answer, I assume the @odata.id property on every value item for this kind of request is required. Yet I can't seem to find a way of creating that property/value in an EdmEntityObject object. Any attempts at assigning a property of that name result in the following exception being thrown:

Microsoft.OData.ODataException: The property name '@odata.id' is invalid; property names must not contain any of the reserved characters ':', '.', '@'.

So is what i'm trying to do supported/possible with the current lib, or am I wasting my time by trying to do something that is not supported for the Dynamic EDM Model use case?

Creating a valid odata.context based on the request might also be a challenge, but i'll cross that bridge if and when i've resolved this @odata.id issue first!