Question

I’m new to MongoDB and was wondering about querying for domain objects with registered BsonClassMaps.
Consider the following Mappings:

BsonClassMap.RegisterClassMap<VoyageNumber>(cm =>
            { cm.MapField<string>(p => p.Id); });

BsonClassMap.RegisterClassMap<Schedule>(cm =>
        { cm.MapField<DateTime>(p => p.EndDate); cm.MapField<DateTime>(p => p.StartDate); });

BsonClassMap.RegisterClassMap<Voyage>(cm =>
            { cm.MapIdField<VoyageNumber>(p => p.VoyageNumber); cm.MapField<Schedule>(p => p.Schedule); });

The domain entity is “Voyage”. In this simple example it consists of a complex type “Schedule” (with start date and end date) and a VoyageNumber (with a string id field).
“VoyageNumber” is the identifier for the entity.

Now I can insert a new voyage just fine with:

MongoCollection<Voyage> mongoVoyages = context.MyDB.GetCollection<Voyage>("Voyages");

mongoVoyages.Insert<Voyage>(voyage);

I can retrieve one Voyage via:

MongoCollection mongoVoyages = context.MyDB.GetCollection("Voyages");

BsonDocument result = mongoVoyages.FindOneAs<BsonDocument>();
BsonDocument sched = result["Schedule"].AsBsonDocument;
DateTime start = sched["StartDate"].AsDateTime;
//etc...

Now of course I’d like to search a voyage by Id. How can I achieve this with the mappings shown above? I tried something like this and failed:

Query.EQ("VoyageNumber", someStringID)

I’m using the official C# driver 1.0.

Answer 1

With above classes registration you will have document like this in mongodb:

{
  "_id": {
    "_id": someStringID
  },
  "Schedule": {
    "EndDate": "Sun, 10 Apr 2011 13:06:25 GMT +03:00",
    "StartDate": "Sun, 10 Apr 2011 13:06:25 GMT +03:00"
  }
}

So if you want get Voyage by VoyageNumber Id you should use following query:

Query.EQ("_id._id", someStringID)

Note: You no need BsonClassMap.RegisterClassMap for class if you map all fileds because it will be serialized by default without any registration. Also you can do custom serialization using attributes like [BsonId], [BsonIgnore]. For more details check documentation or ask another question ;).

From documentation:

You can either create this class map
yourself or simply allow the class map
to be created automatically when first
needed (called “automapping”). You can
exert some control over the
automapping process either by
decorating your classes with
serialization related attributes or by
using initialization code (attributes
are very convenient to use but for
those who prefer to keep serialization
details out of their domain classes be
assured that anything that can be done
with attributes can also be done
without them)