Question

I’m adding CSV export to a service implemented with ASP.NET Web API.

Currently I have a view model (containing details of results filtering), which is sent to a Web API controller via a ajax POST request. The JSON response is then rendered on UI. This works just fine.

Now I want to post the same view model to another controller, let us name it ExportController. Then I need to download the file to the user.

My idea:

1. Post the view model to the service, store it somewhere in persistent storage (DB or in-memory cache, does not matter) and return an export token to a user. (By export token I mean a piece of information used to identify this particular export)

2. Then execute a GET request from an iframe with that token in URL
   and get the file as the response to this request.

What I have by now, on UI:

var exportUrl = "URL to ExportController"
$.ajax(exportUrl, {
   type: 'POST',
   contentType: 'application/json',
   data: postData
})
.success(function(data) {
    // this should download the file
    $('#export').attr('src', exportUrl + '&exportToken=' + data);
});

Here ‘#export’ is the iframe element used to download the file.

And here is a raw sketch of export backend:

public class ExportController : ApiController
{
    ...

    // GET /api/Export
    public string Get(string exportToken)
    {
        // get filters from DB
        var filters = ExportArgumentProvider.GetFilters(exportToken);

        // get data
        var result = DataSource.GetData(filters);

        return result;
    }

    // POST /api/Export
    public string Post(FilterInput filters)
    {
        var guid = Guid.NewGuid();

        // save filters to DB
        ExportArgumentProvider.AddFilter(guid, filters);

        return guid.ToString();
    }
}

This pseudo-code obviously does not work, please ignore the return type of Get method.

So, questions:

1. Is there easier way to make this export (without storing filter state in DB).
2. Is this approach sane (state stored in DB etc.), or such tasks should be done in another way?
3. Is ASP.NET Web API a good fit for such tasks or I should resort to usual ASP.NET controllers for export?

UPDATE: data posted to the server may exceed URL lenght limits, so passing it via a GET request is not really an option.

Answer 1

For this project I gave up creating clean and RESTful backend and converted ExportController into a usual MVC controller. Then I was able to change this line in Post method

ExportArgumentProvider.AddFilter(guid, filters);

into

Session[exportId] = filters;

and do the same thing with the Get method.

I still think that approach with storing filters in DB is much better, but

1. I don’t really need REST API here.
2. It introduces too much overhead into the code, much more than I would like to add ‘just for the sake of purity of the API’.