c# - 将 Dictionary 序列化为 BSON 时出现 BsonSerializationException

Question

我最近搬到了 new MongoDB C# driver v2.0来自 deprecated v1.9 .

现在，当我序列化具有字典的类时，有时会遇到以下 BsonSerializationException:

MongoDB.Bson.BsonSerializationException: When using DictionaryRepresentation.Document key values must serialize as strings.

这是一个最小的复制:

class Hamster
{
    public ObjectId Id { get; private set; }
    public Dictionary<DateTime,int> Dictionary { get; private set; }
    public Hamster()
    {
        Id = ObjectId.GenerateNewId();
        Dictionary = new Dictionary<DateTime, int>();
        Dictionary[DateTime.UtcNow] = 0;
    }
}

static void Main()
{
    Console.WriteLine(new Hamster().ToJson());
}

Answer 1

问题是新驱动默认将字典序列化为文档。

MongoDB C# 驱动程序有 3 种方法来序列化字典:Document、ArrayOfArrays 和 ArrayOfDocuments (more on that in the docs)。当它序列化为文档时，字典键是 BSON 元素的名称，它有一些限制(例如，如错误所示，它们必须序列化为字符串)。

在这种情况下，字典的键是 DateTimes 不是序列化为字符串，而是 Dates 所以我们需要选择另一个 DictionaryRepresentation。

要更改此特定属性的序列化，我们可以使用具有不同 DictionaryRepresentation 的 BsonDictionaryOptions 属性:

[BsonDictionaryOptions(DictionaryRepresentation.ArrayOfArrays)]
public Dictionary<DateTime, int> Dictionary { get; private set; }

但是，我们需要对每个有问题的成员单独执行此操作。要将此 DictionaryRepresentation 应用于所有相关成员，我们可以实现一个新约定:

class DictionaryRepresentationConvention : ConventionBase, IMemberMapConvention
{
    private readonly DictionaryRepresentation _dictionaryRepresentation;
    public DictionaryRepresentationConvention(DictionaryRepresentation dictionaryRepresentation)
    {
        _dictionaryRepresentation = dictionaryRepresentation;
    }
    public void Apply(BsonMemberMap memberMap)
    {
        memberMap.SetSerializer(ConfigureSerializer(memberMap.GetSerializer()));
    }
    private IBsonSerializer ConfigureSerializer(IBsonSerializer serializer)
    {
        var dictionaryRepresentationConfigurable = serializer as IDictionaryRepresentationConfigurable;
        if (dictionaryRepresentationConfigurable != null)
        {
            serializer = dictionaryRepresentationConfigurable.WithDictionaryRepresentation(_dictionaryRepresentation);
        }

        var childSerializerConfigurable = serializer as IChildSerializerConfigurable;
        return childSerializerConfigurable == null
            ? serializer
            : childSerializerConfigurable.WithChildSerializer(ConfigureSerializer(childSerializerConfigurable.ChildSerializer));
    }
} 

我们注册如下:

ConventionRegistry.Register(
    "DictionaryRepresentationConvention",
    new ConventionPack {new DictionaryRepresentationConvention(DictionaryRepresentation.ArrayOfArrays)},
    _ => true);