将 Dictionary 序列化为 BSON 时出现 BsonSerializationException

我最近搬到了新的 MongoDB C# 驱动程序 v2.0 https://www.nuget.org/packages/MongoDB.Driver/2.0.0来自已弃用 v1.9 https://www.nuget.org/packages/mongocsharpdriver/2.0.0.

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

MongoDB.Bson.BsonSerializationException：使用 DictionaryRepresentation.Document 时，键值必须序列化为字符串。

这是一个最小的重现：

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());
}

问题是新驱动程序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 & ArrayOfDocuments (文档中有更多相关内容 http://mongodb.github.io/mongo-csharp-driver/2.2/reference/bson/mapping/#dictionary-serialization-options）。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，正如错误所示，它们必须序列化为字符串）。

在这种情况下，字典的键是DateTimes 没有序列化为字符串，而是序列化为Date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BsonDictionaryOptions具有不同的属性DictionaryRepresentation:

[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。要应用此DictionaryRepresentation对于所有相关成员，我们可以实施一项新公约：

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);