Csharp Mongodb 驱动程序过滤器内的序列化

这是一个棘手而有趣的问题.

如前所述，根据当前查询MongoDB Fluent API will pass the enum value as an integer而不是EnumMemberAttribute中的字符串值，您将枚举值存储为集合中的字符串.

Warning: This will be a long answer.个

这些步骤是为了允许MongoDB fluent API在查询中传递来自EnumMemberAttribute的值.

1. 一种帮助器/扩展方法，允许您从string转换为Enum(实现EnumMemberAttribute，反之亦然.

using System.Linq;
using System.Reflection;
using System.Runtime.Serialization;

public static class EnumExtensions
{
    public static string GetEnumMemberValue<TEnum>(this TEnum @enum)
        where TEnum : struct, Enum
    {
        string enumMemberValue = @enum.GetType()
            .GetMember(@enum.ToString())
            .FirstOrDefault()?
            .GetCustomAttributes<EnumMemberAttribute>(false)
            .FirstOrDefault()?
            .Value;

        if (enumMemberValue == null)
            return @enum.ToString();
            //throw new ArgumentException($"Enum {@enum.GetType().Name} with member {@enum} not apply {nameof(EnumMemberAttribute)} attribute.");

        return enumMemberValue;
    }

    public static TEnum EnumMemberValueToEnum<TEnum>(this string value)
        where TEnum : struct, Enum
    {
        foreach (var field in typeof(TEnum).GetFields())
        {
            if (Attribute.GetCustomAttribute(field,
                typeof(EnumMemberAttribute)) is EnumMemberAttribute attribute)
            {
                if (attribute.Value == value)
                    return (TEnum)field.GetValue(null);
            }

            if (field.Name == value)
                return (TEnum)field.GetValue(null);
        }

        throw new ArgumentException($"{value} is not found.");
    }
}

2. 实现并注册一个自定义序列化程序，用于将string值(从EnumMemberAttribute值)转换为Enum，反之亦然.参考文献:@wilver's answer on Storing Enums as strings in MongoDB

using MongoDB.Bson.Serialization;
using MongoDB.Bson.Serialization.Attributes;
using MongoDB.Bson.Serialization.Serializers;

public class EnumMemberStringSerializer<TEnum> : ObjectSerializer, IBsonSerializer<TEnum>
    where TEnum : struct, Enum
{
    public new Type ValueType => typeof(TEnum);

    public TEnum Deserialize(BsonDeserializationContext context, BsonDeserializationArgs args)
    {
        return EnumExtensions.EnumMemberValueToEnum<TEnum>(base.Deserialize(context, args)?.ToString());
    }

    public void Serialize(BsonSerializationContext context, BsonSerializationArgs args, TEnum value)
    {
        base.Serialize(context, args, EnumExtensions.GetEnumMemberValue((TEnum)value));
    }

    public override void Serialize(BsonSerializationContext context, BsonSerializationArgs args, object value)
    {
        base.Serialize(context, args, EnumExtensions.GetEnumMemberValue((TEnum)value));
    }

    object IBsonSerializer.Deserialize(BsonDeserializationContext context, BsonDeserializationArgs args)
    {
        return EnumExtensions.EnumMemberValueToEnum<TEnum>(base.Deserialize(context, args)?.ToString());
    }
}

3. 注册EnumMemberStringSerializer序列化程序(在创建IMongoDatabase&；IMongoCollection实例之前).

BsonSerializer.RegisterSerializer(typeof(CloudFileTypes), new EnumMemberStringSerializer<CloudFileTypes>());