Ignore null property when deserializing with C# MongoDB driver

Question

I'm using MongoDB C# Driver 3.1.0.

I know how to ignore null properties when serializing by using the IgnoreIfNullConvention, but I'd like to ignore a specific null property when deserializing - is there a way to do this?

Specifically, I'm declaring a property in the class like:

public class X
{
    public ICollection<T> Property { get; set; } = new List<T>();

}

The hope is that Property will never be null. But even with this, if Property already has a null value in MongoDB, the driver is deserializing Property to null and overriding the explicit implementation of new List<T>().

I've tried different versions of this without success:

BsonClassMap.RegisterClassMap<X>(x =>
{
    x.MapField(y => y.Property)
        .SetIsRequired(true)
        .SetDefaultValue(new List<T>());
});

Is there any other way to accomplish this?

Answer 1

In addition to creating a custom serializer, MongoDB C# Driver also supports ISupportInitialize. This can be used to assert that the value is set after deserialization, e.g.:

class MyDocument : ISupportInitialize
{
    // ...    
    public ICollection<string> ListProperty { get; set; } = new List<string>();

    public void BeginInit()
    {
        // Nothing to do here
    }

    public void EndInit()
    {
        ListProperty = ListProperty ?? new List<string>();
    }
}