使用Mongo C＃Driver序列化不可变值类型

Question

我有许多不可变的值类型类，例如EmailAddress，它确保任何非null实例都有效。我想在使用MongoDB C＃Driver持久化时控制这些类型对象的序列化只是标准字符串表示（"[email protected]"）。

我已经尝试实现IBsonSerilizer但是它只允许根级别的对象或数组。我能够用Json.NET实现适当的Json Serilization，我应该采用不同的方法吗？

Answer 1

我假设你的意思是这样的EmailAddress类：

[BsonSerializer(typeof(EmailAddressSerializer))]
public class EmailAddress
{
    private string _value;

    public EmailAddress(string value)
    {
        _value = value;
    }

    public string Value
    {
        get { return _value; }
    }
}

我使用了一个属性将EmailAddress类链接到自定义序列化程序，可以像这样实现：

public class EmailAddressSerializer : BsonBaseSerializer
{
    public override object Deserialize(BsonReader bsonReader, Type nominalType, Type actualType, IBsonSerializationOptions options)
    {
        if (bsonReader.GetCurrentBsonType() == BsonType.Null)
        {
            bsonReader.ReadNull();
            return null;
        }
        else
        {
            var value = bsonReader.ReadString();
            return new EmailAddress(value);
        }
    }

    public override void Serialize(BsonWriter bsonWriter, Type nominalType, object value, IBsonSerializationOptions options)
    {
        if (value == null)
        {
            bsonWriter.WriteNull();
        }
        else
        {
            var emailAddress = (EmailAddress)value;
            bsonWriter.WriteString(emailAddress.Value);
        }
    }
}

您不能将电子邮件地址序列化为根文档（因为它不是文档...）。但您可以使用其他文档中嵌入的电子邮件地址。例如：

public class Person
{
    public int Id { get; set; }
    public EmailAddress EmailAddress { get; set; }
}

您可以使用以下代码进行测试：

var person = new Person { Id = 1, EmailAddress = new EmailAddress("[email protected]") };
var json = person.ToJson();
var rehyrdated = BsonSerializer.Deserialize<Person>(json);

生成的JSON / BSON文档是：

{ "_id" : 1, "EmailAddress" : "[email protected]" }

Answer 2

我试图通过创建一个约定来解决这个问题，该约定映射了与构造函数匹配的所有只读属性以及匹配的构造函数。

假设您有一个类：

public class Person
{
    public string FirstName { get; }
    public string LastName { get; }
    public string FullName => FirstName + LastName;
    public ImmutablePocoSample(string lastName)
    {
        LastName = lastName;
    }

    public ImmutablePocoSample(string firstName, string lastName)
    {
        FirstName = firstName;
        LastName = lastName;
    }
}

这是约定的代码：

/// <summary>
/// A convention that map all read only properties for which a matching constructor is found.
/// Also matching constructors are mapped.
/// </summary>
public class ImmutablePocoConvention : ConventionBase, IClassMapConvention
{
    private readonly BindingFlags _bindingFlags;

    public ImmutablePocoConvention()
            : this(BindingFlags.Instance | BindingFlags.Public)
    { }

    public ImmutablePocoConvention(BindingFlags bindingFlags)
    {
        _bindingFlags = bindingFlags | BindingFlags.DeclaredOnly;
    }

    public void Apply(BsonClassMap classMap)
    {
        var readOnlyProperties = classMap.ClassType.GetTypeInfo()
            .GetProperties(_bindingFlags)
            .Where(p => IsReadOnlyProperty(classMap, p))
            .ToList();

        foreach (var constructor in classMap.ClassType.GetConstructors())
        {
            // If we found a matching constructor then we map it and all the readonly properties
            var matchProperties = GetMatchingProperties(constructor, readOnlyProperties);
            if (matchProperties.Any())
            {
                // Map constructor
                classMap.MapConstructor(constructor);

                // Map properties
                foreach (var p in matchProperties)
                    classMap.MapMember(p);
            }
        }
    }

    private static List<PropertyInfo> GetMatchingProperties(ConstructorInfo constructor, List<PropertyInfo> properties)
    {
        var matchProperties = new List<PropertyInfo>();

        var ctorParameters = constructor.GetParameters();
        foreach (var ctorParameter in ctorParameters)
        {
            var matchProperty = properties.FirstOrDefault(p => ParameterMatchProperty(ctorParameter, p));
            if (matchProperty == null)
                return new List<PropertyInfo>();

            matchProperties.Add(matchProperty);
        }

        return matchProperties;
    }


    private static bool ParameterMatchProperty(ParameterInfo parameter, PropertyInfo property)
    {
        return string.Equals(property.Name, parameter.Name, System.StringComparison.InvariantCultureIgnoreCase)
               && parameter.ParameterType == property.PropertyType;
    }

    private static bool IsReadOnlyProperty(BsonClassMap classMap, PropertyInfo propertyInfo)
    {
        // we can't read 
        if (!propertyInfo.CanRead)
            return false;

        // we can write (already handled by the default convention...)
        if (propertyInfo.CanWrite)
            return false;

        // skip indexers
        if (propertyInfo.GetIndexParameters().Length != 0)
            return false;

        // skip overridden properties (they are already included by the base class)
        var getMethodInfo = propertyInfo.GetMethod;
        if (getMethodInfo.IsVirtual && getMethodInfo.GetBaseDefinition().DeclaringType != classMap.ClassType)
            return false;

        return true;
    }
}

您可以使用以下方式注册我

ConventionRegistry.Register(
    nameof(ImmutablePocoConvention),
    new ConventionPack { new ImmutablePocoConvention() },
    _ => true);

Answer 3

在我读完@Davide Icardi的答案后，我发现在convention中内置了使用不可变对象。

只需注册会议即可

ConventionRegistry.Register(nameof(ImmutableTypeClassMapConvention), 
new ConventionPack { new ImmutableTypeClassMapConvention()}, type => true);