How to apply BsonRepresentation attribute by convention when using MongoDB

问题

I'm trying to apply [BsonRepresentation(BsonType.ObjectId)] to all ids represented as strings withoput having to decorate all my ids with the attribute.

I tried adding the StringObjectIdIdGeneratorConvention but that doesn't seem to sort it.

Any ideas?

回答1:

Yeah, I noticed that, too. The current implementation of the StringObjectIdIdGeneratorConvention does not seem to work for some reason. Here's one that works:

public class Person
{
    public string Id { get; set; }
    public string Name { get; set; }
}

public class StringObjectIdIdGeneratorConventionThatWorks : ConventionBase, IPostProcessingConvention
{
    /// <summary>
    /// Applies a post processing modification to the class map.
    /// </summary>
    /// <param name="classMap">The class map.</param>
    public void PostProcess(BsonClassMap classMap)
    {
        var idMemberMap = classMap.IdMemberMap;
        if (idMemberMap == null || idMemberMap.IdGenerator != null)
            return;
        if (idMemberMap.MemberType == typeof(string))
        {
            idMemberMap.SetIdGenerator(StringObjectIdGenerator.Instance).SetSerializer(new StringSerializer(BsonType.ObjectId));
        }
    }
}

public class Program
{
    static void Main(string[] args)
    {
        ConventionPack cp = new ConventionPack();
        cp.Add(new StringObjectIdIdGeneratorConventionThatWorks());
        ConventionRegistry.Register("TreatAllStringIdsProperly", cp, _ => true);

        var collection = new MongoClient().GetDatabase("test").GetCollection<Person>("persons");

        Person person = new Person();
        person.Name = "Name";

        collection.InsertOne(person);

        Console.ReadLine();
    }
}

回答2:

You could programmatically register the C# class you intend to use to represent the mongo document. While registering you can override default behaviour (e.g map id to string):

public static void RegisterClassMap<T>() where T : IHasIdField
{
    if (!BsonClassMap.IsClassMapRegistered(typeof(T)))
    {
        //Map the ID field to string. All other fields are automapped
        BsonClassMap.RegisterClassMap<T>(cm =>
        {
            cm.AutoMap();
            cm.MapIdMember(c => c.Id).SetIdGenerator(StringObjectIdGenerator.Instance);
        });
    }
}

and later call this function for each of the C# classes you want to register:

RegisterClassMap<MongoDocType1>();
RegisterClassMap<MongoDocType2>();

Each class you want to register would have to implement the IHasIdField interface:

public class MongoDocType1 : IHasIdField
{
    public string Id { get; set; }
    // ...rest of fields
}

The caveat is that this is not a global solution and you still have to manually iterate over your classes.

来源：https://stackoverflow.com/questions/45043266/how-to-apply-bsonrepresentation-attribute-by-convention-when-using-mongodb

标签

mongodb

mongodb-.net-driver