MongoDB - Mapping map-reduce collections in C#

Question

I am running a map reduce job that dumps the resulting data into a collection, the elements in the "products" collection look like this (the structure is generated by Mongo and I'm not aware if it can be controlled):

{
    "_id" : { "ProductId" : "1:000001", "ProductTitle" : "Some product with ID 1:000001" }, 
    "value" : { "TotalImpressions" : 3, "TotalClicks" : 40 } 
}

Ideally, I want to map each entry to the following flat object:

public class Product 
{
    public string ProductId { get; set; }
    public string ProductTitle { get; set; }
    public int TotalImpressions { get; set; }
}

This obviously doesn't work as the serializer looks for properties "id" and "value" at the root level, which don't exist on that class. The workaround I have in place is to model the object as they appear, e.g.:

public class ProductRow
{
    /* implementation of these objects excluded, but they just reflect the json objects */
    public ProductIdentifier Id { get; set; }
    public Product value { get; set; }
}

Which maps fine, however it's a little verbose and I'd rather avoid having all those extra objects.

Is it possible to configure the BSON deserializer to support this mapping? I've had a look through the documentation, but haven't seen any obvious solution.

NB: I am restricted by working environment to .NET 3.5, so please bear that in mind when considering an answer.

Can't you just map the untyped results to Product instances yourself, after the query? Why do you want the BSON deserializer to do this for you? It's not strictly its job... — Avish, Jun 27 '11 at 13:28
Yes, I could do it manually, which is a valid point - so thanks. But I disagree that this is not a function of the deserializer, it is exactly a problem in it's domain, albeit one which I accept is not likely to be implemented due to the fact is arguably an edge case, hence the question. — gooid, Jun 28 '11 at 08:25

score 4 · Accepted Answer · answered Jun 27 '11 at 19:51

You can easy do deserialization yourself(as @Avish suggested), so here is complete example for your case:

var mongoServer = MongoServer.Create("mongodb://localhost:27020");
var database = mongoServer.GetDatabase("StackoverflowExamples");
var products = database.GetCollection("products");

var result = new Product();

var item = products.FindOne();
var id = item["_id"].ToBsonDocument();
var value = item["value"].ToBsonDocument();

result.ProductId = id["ProductId"].AsString;
result.ProductTitle = id["ProductTitle"].AsString;
result.TotalImpressions = value["TotalImpressions"].AsInt32;

MongoDB - Mapping map-reduce collections in C#

1 Answers1