BsonDocument contains an array. Need to access the array elements in C# when the BsonDocument is contained by a C# list

Question

I have a mongodb collection "users" which stores documents in the following format -

{
    "_id" : ObjectId("53fe7ae0ef038fee879263d5"),
    "username" : "John"
    "status" : "online",
    "profile" : [ 
        {
            "name" : "John Stuart",
            "age" : "23",
            "gender" : "male"
        }
    ]
}

I use the following function in C#.NET to store documents from the collection into a list of BsonDocuments -

    public static List<BsonDocument> LoadDataByWhere (string table, string whereClause)
    {
        // Here table is the collection name and whereClause is the mongodb query 

        var collection = db.GetCollection (table);
        QueryDocument whereDoc = new QueryDocument(BsonDocument.Parse(whereClause));
        var resultSet = collection.Find (whereDoc);
        List<BsonDocument> docs = resultSet.ToList();

        if (resultSet.Count() > 0) {
            foreach(BsonDocument doc in docs)
            {
                doc.Set("_id", doc.GetElement("_id").ToString().Split('=')[1]);
            }
            return docs;
        } 
        else {
            return null;
        }
    }

Supposing that I store the List returned in list. I can use -

    List<string> username = new List<string>();

    foreach(BsonDocument item in list) 
    {
        username.Add(Convert.ToString(list.getElement("username").Value));
    }

But how do I get the array element values like name, age and gender in C# using methods similar to the one described above?

Answer 1

I would recommend mapping the Mongo document to some form of DTO. Mongo supports deserializing into object graphs.

public class User
{   
    [BsonId]
    public ObjectId Id { get; set; }

    public string username { get; set; }

    public string status { get; set; }

    public List<Profile> profile { get; set; }
}


public class Profile
{

    public string name { get; set; }

    public string age { get; set; }

    public string gender { get; set; }
}

Then you can access it something like this

const string connectionString = "mongodb://localhost";

//// Get a thread-safe client object by using a connection string
var mongoClient = new MongoClient(connectionString);

//// Get a reference to a server object from the Mongo client object
var mongoServer = mongoClient.GetServer();

//// Get a reference to the database object
//// from the Mongo server object
const string databaseName = "mydatabase";
var db = mongoServer.GetDatabase(databaseName);

//// Get a reference to the collection object from the Mongo database object
//// The collection name is the type converted to lowercase + "s"
MongoCollection<T> mongoCollection = db.GetCollection<T>(typeof(T).Name.ToLower() + "s");

So when you query by id now it will contain the populated list of profiles, if they exist

use-csharp-driver

mongodb-with-c-deep-dive