c#自定义DynamicObject转换为派生对象

Question

我有一个类DocumentObject，它扩展了DynamicObject以允许动态成员属性。

public class DocumentObject : DynamicObject
{
/// <summary>
/// Inner dictionary that holds the dynamic members of the object
/// </summary>
Dictionary<string, object> dictionary = new Dictionary<string, object>();
/// <summary>
/// Try to get the member that is not defined in the class (additional dynamic members) from inner dictionary
/// </summary>
/// <param name="binder"></param>
/// <param name="result"></param>
/// <returns></returns>
public override bool TryGetMember(GetMemberBinder binder, out object result)
{
// Converting the property name to lowercase
// so that property names become case-insensitive.
string name = binder.Name.ToLower();
// If the property name is found in a dictionary,
// set the result parameter to the property value and return true.
// Otherwise, return false.
return dictionary.TryGetValue(name, out result);
}
/// <summary>
/// Try to set the member that is not defined in the class (additional dynamic members) to inner dictionary
/// </summary>
/// <param name="binder"></param>
/// <param name="value"></param>
/// <returns></returns>
public override bool TrySetMember(SetMemberBinder binder, object value)
{
// Converting the property name to lowercase
// so that property names become case-insensitive.
dictionary[binder.Name.ToLower()] = value;
// You can always add a value to a dictionary,
// so this method always returns true.
return true;
}
/// <summary>
/// Get the names of all the dynamic members
/// </summary>
/// <returns></returns>
public override IEnumerable<string> GetDynamicMemberNames()
{
return dictionary.Keys;
}
}

我有一个继承了DocumentObject的Person基类

public class PersonDto : DocumentObject
{
[JsonProperty("id")]
public string Id { get; set; }
}

继承PersonDto的另一个子类OfficePersonDto

public class OfficePersonDto : PersonDto 
{
[JsonProperty("name")]
public string Name { get; set; }
}

在我的函数中，我正在接收JSON对象，必须至少是PersonDto对象，但如果它是一个OfficePersonDto类型，我希望能够将PersonDto转换为OfficePersonDto。即JSON = {"Id":1, "Name": "Orchard"}，在PersonDto中，name属性将使用DocumentObject的字典保存，而转换到OfficePersonDto时，Id和name都是类的属性。

如何从PersonDto转换为子类，例如OfficePersonDto?

PersonDto personDto = ...
OfficePersonDto off = personDto as OfficePersonDto  // results in null or Name is null

Answer 1

Automapper在这类转换问题上非常有用。我将向您展示一个快速的工作示例。当然，它仍然对更多的重构是开放的。

PersonDto personDto = ...
// Do not use the following conversion, instead get help from automapper
// OfficePersonDto off = personDto as OfficePersonDto

var config = new MapperConfiguration(cfg =>
{
cfg.CreateMap<PersonDto, OfficePersonDto>()
.ForMember(d => d.Name, opt => opt.MapFrom(new OfficePersonNameResolver()));
});

var mapper = config.CreateMapper();
var off = mapper.Map<OfficePersonDto>(personDto); // off is created with correct values

officepersonnamesolver是这样的:

public class OfficePersonNameResolver : IValueResolver<PersonDto, OfficePersonDto, string>
{
public string Resolve(PersonDto source, OfficePersonDto destination, string destMember, ResolutionContext context)
{
return (source as dynamic).Name;
}
}

如果您对此有任何疑问，欢迎提问。

编辑:将解析器泛化为IValueResolver<TSource,>

像这样更改配置的创建:

var config = new MapperConfiguration(cfg =>
{
cfg.CreateMap<PersonDto, OfficePersonDto>()
.ForMember(d => d.Name, opt => opt.MapFrom(new DynamicObjectValueResolver<PersonDto, OfficePersonDto, string>("name")));
});

值解析器现在应该是这样的:

public class DynamicObjectValueResolver<TSource, TDestination, TDestinationMember> : IValueResolver<TSource, TDestination, TDestinationMember>
where TDestinationMember : class
{
private readonly string _propertyName;
public DynamicObjectValueResolver(string propertyName)
{
_propertyName = propertyName;
}
public TDestinationMember Resolve(TSource source, TDestination destination, TDestinationMember destMember, ResolutionContext context)
{
dynamic eo = JsonConvert.DeserializeObject<ExpandoObject>(JsonConvert.SerializeObject(source));
IDictionary<string, object> dictionary = eo;
return dictionary[_propertyName] as TDestinationMember;
}
}

工作示例:https://dotnetfiddle.net/KS91To