用Mongo c#驱动程序序列化不可变值类型

我想你的意思是EmailAddress类是这样的:

[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器，它可以这样实现:

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);
        }
    }
}

你不能序列化一个EmailAddress作为根文档(因为它不是一个文档…)但是您可以使用嵌入在其他文档中的EmailAddress。例如:

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

可以使用下面的代码进行测试:

var person = new Person { Id = 1, EmailAddress = new EmailAddress("joe@xyz.com") };
var json = person.ToJson();
var rehyrdated = BsonSerializer.Deserialize<Person>(json);

生成的JSON/BSON文档为:

{ "_id" : 1, "EmailAddress" : "joe@xyz.com" }

在我阅读了@Davide Icardi的答案后，我发现使用不可变对象是内置的约定。

只需注册约定

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

我试图通过创建映射所有与构造函数匹配的只读属性以及匹配的构造函数的约定来解决这个问题。

假设你有一个这样的类:

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;
    }
}

约定的代码如下:

/// <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:

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