MongoDB C# Driver - Ignore fields on binding

Question

When using a FindOne() using MongoDB and C#, is there a way to ignore fields not found in the object?

EG, example model.

public class UserModel
{
    public ObjectId id { get; set; }
    public string Email { get; set; }
}

Now we also store a password in the MongoDB collection, but do not want to bind it to out object above. When we do a Get like so,

  var query = Query<UserModel>.EQ(e => e.Email, model.Email);
  var entity = usersCollection.FindOne(query);

We get the following error

Element 'Password' does not match any field or property of class 

Is there anyway to tell Mongo to ignore fields it cant match with the models?

Answer 1

Yes. Just decorate your UserModel class with the BsonIgnoreExtraElements attribute:

[BsonIgnoreExtraElements]
public class UserModel
{
    public ObjectId id { get; set; }
    public string Email { get; set; }
}

As the name suggests, the driver would ignore any extra fields instead of throwing an exception. More information here - Ignoring Extra Elements.

Answer 2

Yet Another possible solution, is to register a convention for this.

This way, we do not have to annotate all classes with [BsonIgnoreExtraElements].

Somewhere when creating the mongo client, setup the following:

        var pack = new ConventionPack();
        pack.Add(new IgnoreExtraElementsConvention(true));
        ConventionRegistry.Register("My Solution Conventions", pack, t => true);

Answer 3

Yes. Another way (instead of editing you model class) is to use RegisterClassMap with SetIgnoreExtraElements.

In your case just add this code when you initialize your driver:

BsonClassMap.RegisterClassMap<UserModel>(cm =>
{
     cm.AutoMap();
     cm.SetIgnoreExtraElements(true);
});

You can read more about ignoring extra elements using class mapping here - Ignoring Extra Elements.