CODEWITHSUNDEEP
mongodb-.net-driver
MrX
MrX

Reputation: 424

BsonDefaultValue set to empty list

Simple question how do you set the default value of a BsonValue to an empty List

    [BsonElement("Networks")]
    [BsonRepresentation(BsonType.String)]
    [BsonIgnoreIfNull]
    [BsonDefaultValue(new List<SocialProfileTypes>() { })]
    [BsonIgnoreIfDefault]
    public UniqueList<SocialProfileTypes> Networks
    {
        get { return networks; }
        set { networks = value; }
    }

As [BsonDefaultValue(new List<SocialProfileTypes>() { })] gives a syntax error 

Error   8   An attribute argument must be a constant expression, typeof expression or array creation expression of an attribute parameter type

Upvotes: 3

Views: 2851

Answers (2)

fatih b&#252;lb&#252;l
fatih b&#252;lb&#252;l

Reputation: 21

I solved my similar problem.

My Startup.cs file

public class Startup
{
    // Other codes .....
    public void ConfigureServices(IServiceCollection services)
    {
        // Other codes .....

        // Register custom array serializer
        BsonSerializer.RegisterGenericSerializerDefinition(typeof(IEnumerable<>), typeof(MongoDBCustomArraySerializer<>));

        // Other codes .....
    }
}

My CustomSerializer

public class MongoDBCustomArraySerializer<T> : ArraySerializer<T>
{
    public override void Serialize(BsonSerializationContext context, BsonSerializationArgs args, T[] value)
    {
        // Serializer empty array when array is null
        if (value == null)
            base.Serialize(context, args, Array.Empty<T>());
        else
            base.Serialize(context, args, value);
    }
}

Upvotes: 0

Craig Wilson
Craig Wilson

Reputation: 12624

This is a C# language constraint. Values in attributes must be compile time constants.

With regards to the mongodb driver, you'll need to use code to set the value like this (note: have no compiled this, but it will be similar)

BsonClassMap.RegisterClassMap<MyClass>(cm =>
  cm.AutoMap();
  cm.MapMember(x => x.Networks).SetDefaultValue(new List<SocialProfileTypes>())
});

I believe this is going to fail anyways because List doesn't implement or inherit from UniqueList, so you'll have to fix that too.

Upvotes: 2

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