序列化 MongoDb 上的 get-only 属性

Question

使用 C# 6 我可以编写：

public class Person
{
    public Guid Id { get; }
    public string Name { get; }
    public Person(Guid id, string name)
    {
        Id = id;
        Name = name;
    }
}

不幸的是，像这样的类没有被 MongoDb 驱动正确序列化，属性没有序列化。

MongoDb 仅默认使用 getter 和 setter 序列化属性。我知道您可以手动更改类映射并将序列化程序告诉include get-only properties，但我正在寻找一种通用方法来避免自定义每个映射。

我正在考虑创建一个类似于ReadWriteMemberFinderConvention 但没有CanWrite 检查的自定义约定。

还有其他解决方案吗？构造函数将被自动调用还是我需要一些其他的自定义？

Answer 1

更新：MongoDB.Bson 2.10 版现在带有 ImmutableTypeClassMapConvention

---

我试图通过创建一个映射所有与构造函数以及匹配的构造函数匹配的只读属性的约定来解决此问题。

假设您有一个不可变的类，例如：

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：

using MongoDB.Bson.Serialization;
using MongoDB.Bson.Serialization.Conventions;
using System.Collections.Generic;
using System.Linq;
using System.Reflection;

/// <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 i：

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

Answer 2

如果您不希望所有只读属性都被序列化，您可以添加一个什么都不做的公共集（如果适用），请注意，当您的类被反序列化时，该属性将被重新评估。

public class Person
{
    public string FirstName { get; }
    public string LastName { get; }
    public string FullName
    {
        get
        {
            return FirstName + LastName;
        }
        set
        {
           //this will switch on the serialization
        }
    }
}

Answer 3

我遇到了同样的问题，发现接受的答案过于复杂。

相反，您可以简单地将 BsonRepresentation 属性添加到您想要序列化的只读属性中：

public class Person
{
    public string FirstName { get; }

    public string LastName { get; }

    [BsonRepresentation(BsonType.String)]
    public string FullName => $"{FirstName} {LastName}";
}

Answer 4

假设您有一个不可变的类，例如：

public class Person
{
    public string FirstName { get; }

    public string LastName { get; }

    [BsonRepresentation(BsonType.String)]
    public string FullName => $"{FirstName} {LastName}";
}

只需添加 [BsonElement] 结果

public class Person
{
    [BsonElement]
    public string FirstName { get; }

    [BsonElement]
    public string LastName { get; }

    public string FullName => $"{FirstName} {LastName}";
}