Mongo db C# serialization

Question

I'm trying to write the following code using 10gen C# drivers for Mongo Db. What I'm trying to achieve here is that write a simple adapter so as to seamlessly cache C# objects.

The RegisterClassMap() is not able to recognize CacheId field from the class contract. I couldn't find enough documentation on MapIdField api.

Can somebody please help ? Thanks in advance !!

public interface ICacheable
{
    byte[] CacheId { get; }
}

public class Contract : ICacheable
{
    public byte[] CacheId { get; set; }

    public string Name { get; set; }

    public string Description { get; set; }
}

public class MongoCacheStore
{
    private void RegisterClass<T>() where T : class, ICacheable
    {
        if (!BsonClassMap.IsClassMapRegistered(typeof(T)))
        {
            BsonClassMap.RegisterClassMap<T>();

            BsonClassMap.RegisterClassMap<T>(cm =>
            {
                cm.AutoMap();
                **cm.MapIdField("CacheId");**
            });
        }
    }
}

I also changed cm.MapIdField("CacheId"); to cm.MapIdField("Id"); and declared Id as long datatype. But still it couldn't recognize Id. So it is not related about not been able to identify byte array id field — BlitzKrieg
– BlitzKrieg, Commented Feb 14, 2012 at 18:51

Robert Stam · Accepted Answer · 2012-02-14 23:38:41Z

4

The following worked for me:

public class MongoCacheStore
{
    public void RegisterClass<T>() where T : class, ICacheable
    {
        BsonClassMap.RegisterClassMap<T>(cm =>
        {
            cm.AutoMap();
            cm.MapIdProperty("CacheId");
        });
    }
}

You have to use MapIdProperty instead of MapIdField because CacheId is a property.

Did you mean to not have a set accessor in the interface?

Also, it is much better if you arrange to have RegisterClass only called once rather then testing for IsClassMapRegistered every time. For one, I don't think it is thread safe as written (two threads could both get false back from calling IsClassMapRegistered and one of them is going to fail when calling RegisterClassMap).

answered Feb 14, 2012 at 23:38

Robert Stam

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3 Comments

BlitzKrieg Over a year ago

Thanks for replying Robert. Yes I meant to not have set accessor in the interface. Is it possible in anyway that I use CacheId as the _id field for that document but not serialize it. Something like this code public class MongoCacheStore { public void RegisterClass<T>() where T : class, ICacheable { BsonClassMap.RegisterClassMap<T>(cm => { cm.AutoMap(); cm.MapIdProperty("CacheId"); ** cm.SkipFromSerialization("CacheId"); }); } }

BlitzKrieg Over a year ago

Pardon me for the lack of indentation the above comment

Robert Stam Over a year ago

Even if you were to configure your class map so that the _id is not serialized the server will add one anyway when you insert the document. The _id field is mandatory.

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