MongoDB, C#, Linq, Query, Update on a generic List item

Question

I am new to the MongoVerse, but my problem is as follows:

var connectionString = "mongodb://localhost";
var client = new MongoClient(connectionString);
var server = client.GetServer();
var database = server.GetDatabase("test");
var collection = database.GetCollection<Entity>("entities");

var entity = new Entity { Name = "Tom" };
collection.Insert(entity);
var id = entity.guid;

var query = Query<Entity>.EQ(e => e.guid, id);

var entity2 = collection.FindOne(query);
Console.WriteLine("Getting entity2 works!");

for (int i = 0; i < 100; i++)
{
     var ourPoint = ((MongoQueryable<List<SubEntity<object>>>)(from q in collection.AsQueryable<Entity>() where q.guid == id select q.thePackage)).GetMongoQuery();
     var ourUpdate = Update<List<SubEntity<object>>>.Set(q => q[i], new SubEntity<object>() { value = 3.14 });
     collection.Update(ourPoint, ourUpdate);
}

var entity3 = collection.FindOne(query);
Console.WriteLine("Getting entity3 throws an error!");

System.IO.FileFormatException: Element '0' does not match any field or property of class namespace+Entity

The class I'm serializing is as follows:

public class Entity
{
    [BsonId]
    public ObjectId guid = new ObjectId();
    public string Name = "";
    public List<SubEntity<object>> thePackage = new List<SubEntity<object>>();

    public Entity()
    {
        for (int i = 0 ; i < 100; i++)
        {
            thePackage.Add(new SubEntity<object>() { value = Math.PI });
        }
    }
}

The subclass is:

public class SubEntity<T>
{
    public DateTime dateTime = DateTime.Now;
    public T value = default(T);
}

I suspect, the Linq query isn't supported, or isn't occurring properly. What I see from the documentation, is that the Select query is preformed client side, but using StopWatches, the time needed to perform the Operation appear right (vs. over-writing an entire List<>).

I read some stuff on Data Analysis Schema (on Mongo's site), the popular scheme, seems to involve creating a document with an array full of blank entries (for the hour, day, week, depending on how often you're taking a number), and then writing one value at time.

I'm curious about the Linq issue? Anyone know what my next stop would be? But, I really just want to get a good example of how to update 1 value at a time from an array. (Where I may not know the data type, or the array size ahead of time)

I will keep looking (its quite late atm, so my search may be postponed), and I will post back my answer if I discover one.

I am using MongoDB 2.6 Standard for Windows 8 (64 bit windows and mongo). I've also reproduced the bug on a Windows 7 machine as well.

I never found the answer, but I changed my approach. (10/9/2014)

I did the serialization myself with the BsonDocument classes. Write times went from 60ms to less than 1ms. Replacing one item in list before took about 6 ms. I still am not sure how to replace an arbitrary BsonArray element, but its fast enough that it is no longer an issue.

Answer 1

This line isn't supported:

Update<List<SubEntity<object>>>.Set(q => q[i], new SubEntity<object>() { value = 3.14 });

We need an element name in the first argument, and q[i] is not one. However, this looks like a bug we should fix. Feel free to file a Jira ticket at jira.mongodb.org under the CSHARP project.

For now, you'll need to resort to using the untyped query builder.