CODEWITHSUNDEEP
c#.netmongodbfind
user3471066
user3471066

Reputation: 179

.Net MongoDB, Finding documents of custom class

Here is the sample data from a collection. Basically the only thing that I am trying to do is read all of the data like this in as a "Student" but it is throwing an error for some reason. It works fine when I read them all in as Bson documents but that is not what I want to do. Here is the error:

An unhandled exception of type 'System.AggregateException' occurred in mscorlib.dll

Additional information: One or more errors occurred.

what am I doing wrong?

{ "_id" : 137, "name" : "Tamika Schildgen", "scores" : [ { "type" : "exam", "score" : 4.433956226109692 }, { "type" : "quiz", "score" : 65.50313785402548 }, { "type" : "homework", "score" : 89.5950384993947 } ] }

    static async Task MainAsync(string[] args)
    {
        var client = new MongoClient();
        var db = client.GetDatabase("school");
        var col = db.GetCollection<Student>("students");

        var list = await col.Find(new BsonDocument())
            .ToListAsync();

        foreach(var doc in list)
        {
            Console.WriteLine(doc);
        }

    }
}

class Student
{
    public ObjectId Id { get; set; }
    public string name { get; set; }
    public Scores[] scores { get; set; }

}
class Scores
{
    public string type { get; set; }
    public double score { get; set; }
}

Upvotes: 0

Views: 1170

Answers (1)

Piotr Kasprzyk
Piotr Kasprzyk

Reputation: 81

The error lies in Id field type:

If you turn on the option of breaking execution when a CLR exception is thrown (Menu Debug|Exceptions), you will see a message similar to: "An error occurred while deserializing the Id property of class ConsoleApplication2.Student: Cannot deserialize a 'ObjectId' from BsonType 'Double'."

If you change the class Student to:

          public class Student
          {
            public int Id { get; set; }
            public string name { get; set; }
            public Scores[] scores { get; set; }
          }

the exception will not be thrown anymore.

(Additionally, to get readable results, you should probably override ToString() method for Student class).

Upvotes: 1

Related Questions