将 Dictionary<DateTime,T> 序列化为 BSON 时出现 BsonSerializationException

Question

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

现在，当我将具有字典的 class 序列化时，有时运行会变成以下 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

问题是新驱动程序默认将字典序列化为文档。

MongoDB C# 驱动程序有 3 种序列化字典的方法：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，如错误提示，它们必须序列化为字符串）。

在这种情况下，字典的键是 DateTime，它没有序列化为字符串，而是 Date，因此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，我们可以实施一个新约定：

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));
    }
}

其中我们注册如下：

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

Answer 2

上面的答案很好，但不幸的是在某些递归对象层次结构上触发了 WhosebugException - 这是一个略有改进的最新版本。

public class DictionaryRepresentationConvention : ConventionBase, IMemberMapConvention
{
    private readonly DictionaryRepresentation _dictionaryRepresentation;

    public DictionaryRepresentationConvention(DictionaryRepresentation dictionaryRepresentation = DictionaryRepresentation.ArrayOfDocuments)
    {
        // see http://mongodb.github.io/mongo-csharp-driver/2.2/reference/bson/mapping/#dictionary-serialization-options

        _dictionaryRepresentation = dictionaryRepresentation;
    }

    public void Apply(BsonMemberMap memberMap)
    {
        memberMap.SetSerializer(ConfigureSerializer(memberMap.GetSerializer(),Array.Empty<IBsonSerializer>()));
    }

    private IBsonSerializer ConfigureSerializer(IBsonSerializer serializer, IBsonSerializer[] stack)
    {
        if (serializer is IDictionaryRepresentationConfigurable dictionaryRepresentationConfigurable)
        {
            serializer = dictionaryRepresentationConfigurable.WithDictionaryRepresentation(_dictionaryRepresentation);
        }

        if (serializer is IChildSerializerConfigurable childSerializerConfigurable)
        {
            if (!stack.Contains(childSerializerConfigurable.ChildSerializer))
            {
                var newStack = stack.Union(new[] { serializer }).ToArray();
                var childConfigured = ConfigureSerializer(childSerializerConfigurable.ChildSerializer, newStack);
                return childSerializerConfigurable.WithChildSerializer(childConfigured);
            }
        }

        return serializer;
    }

Answer 3

如果你像我一样只是想将它应用于 class 中的单个字段，我是这样实现的（感谢其他答案）：

BsonClassMap.RegisterClassMap<TestClass>(cm =>
{
    cm.AutoMap();
    var memberMap = cm.GetMemberMap(x => x.DictionaryField);
    var serializer = memberMap.GetSerializer();
    if (serializer is IDictionaryRepresentationConfigurable dictionaryRepresentationSerializer)
        serializer = dictionaryRepresentationSerializer.WithDictionaryRepresentation(DictionaryRepresentation.ArrayOfDocuments);
    memberMap.SetSerializer(serializer);
});

或作为扩展方法：

BsonClassMap.RegisterClassMap<TestClass>(cm =>
{
    cm.AutoMap();
    cm.SetDictionaryRepresentation(x => x.DictionaryField, DictionaryRepresentation.ArrayOfDocuments);
});

public static class MapHelpers
{
    public static BsonClassMap<T> SetDictionaryRepresentation<T, TMember>(this BsonClassMap<T> classMap, Expression<Func<T,TMember>> memberLambda, DictionaryRepresentation representation)
    {
        var memberMap = classMap.GetMemberMap(memberLambda);
        var serializer = memberMap.GetSerializer();
        if (serializer is IDictionaryRepresentationConfigurable dictionaryRepresentationSerializer)
            serializer = dictionaryRepresentationSerializer.WithDictionaryRepresentation(representation);
        memberMap.SetSerializer(serializer);
        return classMap;
    }
}

将 Dictionary<DateTime,T> 序列化为 BSON 时出现 BsonSerializationException

BsonSerializationException when serializing a Dictionary<DateTime,T> to BSON

.net

c#

mongodb

mongodb-csharp-2.0

mongodb-.net-driver