I have data stored in an instance of a class which has been serialized with the .net BinaryFormatter. I now want to rename one of the fields in the class, but still be able to deserialize the old data.
One option is to implement ISerializable and deserialize all the the fields of the class manually. But this seems like a lot of work, especially if my class has lots of fields and I've only renamed a single field.
Is there a better way?
Craig suggests keeping a copy of the old class for deserialization, and copying values to the new class. I've seen this suggested elsewhere too - what advantage does this have over implementing ISerializable? As far as I can see, copying the class leaves me with 2 almost identical copies of the class plus I still have to copy all the values from the old class to the new class - which seems the same amount of work as implementing ISerializable with an almost duplicate class thrown into mix.
Two answers have mentioned Binders. I've successfully used a SerializationBinder to deserialize a class Bar which was Serialized as class Foo, but that's because the name of the class changed. Does SerializationBinder also help when you've renamed a field - say when int m_Left has been renamed to int m_Right?
Yes, this is the problem with field-based serializers. You can use either a custom Binder, or a "serialization surrogate" to avoid implementing ISerializable, but that is only a case-by-case fix.
I've discussed this topic (in the context of obfuscators, and auto-props) here. My advice is: don't use BinaryFormatter for persistance of data between versions... for that, look at contract-based serializers:
XmlSerializer
DataContractSerializer
or for binary, things like protobuf-net
None of this helps you today, but it might help you design around it in the future.
You could try having the old calss hang around for the sole purpose of rehydration and then just copy over the fields you need to the new class. Still kind of painful but should work.
I used SerializationBinder class for this before
http://msdn.microsoft.com/en-us/library/system.runtime.serialization.serializationbinder.aspx
it can be used for deserialization so you can remap old type to new one.
What if you just change the access modifier on that one property to private, and then have a public property with the new name that just basically wraps the old one. That way you should still be able to deserialize (I THINK) but anyone using this class won't know about the old name. Just a thought...
Related
Even if you don't apply SerializableAttribute or ISerializable, every serializer that I know of does a good job of serializing objects anyway - So when is it a good idea, or a requirement, to use [Serializable] or ISerializable?
I understand [Serializable] and ISerializable are available whenever the default serialization behavior is undesired, such as, you want to exclude some public properties, or include some private ones. Is that the only situation where you need to, or should, use SerializableAttribute and ISerializable?
When you want to export a instance of object with setting in memory into a file and load again the next time you want to used just with the same settings and values before you saved.
This Link will explain you much better and is awesome the things you canto with it.
i want to implement a general Memento-Pattern in C#. It is working fine but i use the Serializeable() Attribute to do a deep copy of a object. My implementation using generics so if someone use it he has to give his class as type.
Now the class from user must have the Attribute Serializeable() too. Are there any limitations for a class which using Serializeable()?
In fact:
Are there any performance problems?
Is it possible to use an interface?
Is it possible to use inerhitence?
Is it possible to use Auto-Properties?
I dont know how the Attribute works and so iam a bit scary of using this in such a global way.
regards
for small models that you are cloning in memory, not usually
irrelevent; when using [Serializable] you are typically using BinaryFormatter - which looks at the objects themselves; it doesn't matter what interfaces they implement - the interfaces are not used
yes, for the same reason - but all types in the model must be [Serializable]
yes, for the same reason; note : the default BinaryFormatter implementation is looking at fields - it won't even touch the properties
Personally, I try to advise against BinaryFormatter, but this is perhaps not an unreasonable use. However! Be careful that it is easy to suck extra objects into the model accidentally, must commonly through events. Note that it is a good idea to mark all events as non-serialized:
[field:NonSerialized]
public event EventHandler Something;
(or apply to the field directly if using explicit add/remove accessors)
Note also that any members like:
public object Tag {get;set;} // caller-defined
should also probably be [field:NonSerialized].
Personally, I'd prefer a different serializer, but: this will often work. I will say, though: try to avoid persisting the output of BinaryFormatter, as it is hard to guarantee compatibility between revisions of your code.
I dont know how the Attribute works
It does nothing at all except add an IL flag that says "by the way, consider this ok to be serialized"; actually, most serializers don't even look at this flag - but BinaryFormatter is one of the few that do look at this flag. The real code here is BinaryFormatter, which basically does:
have I seen this object before? if so, store the key only
what type is it? is it [Serializable]? store the type info
invent a new reference and store that as the identity
does it have a custom serializer? if so: use that
what fields does it have? access each in turn and store the name/value pair
Serialization woes continue...
I'm trying to serialize a class, instances of which share between them common objects (a binder of sorts). So, objects A, B, C share object Binder1, and objects D and E - Binder2, and so on... I'm serializing objects A,B,C,D,E. Typically, this binder object is passed in a constructor - not with the serializer though, since it needs a parameterless constructor.
ISeriazable seems to have something that works for singletons - IObjectReference interface, where the method GetRealObject can be used to return a reference to the newly created singleton. But, it doesn't look like XmlSerializer cares about this interface.
So, how should I go about serializing/deserializing these objects?
EDIT: I'm almost ready to give up on this question, since I just discovered this question discussed on a forum from 2006 (!!) between two giants #JonSkeet and #MarcGravell, where the answer is essentially no for XmlSerializer. I'll keep this question open for a bit longer just in case things have changed in the past 7 years.
I haven't found a way to do this natively with XmlSerializer. I did find an old thread between Jon Skeet and Marc Gravell that basically says that you can't do this the same way that you could with ISerializable and IObjectReference.
The way I had to make this work was along the following lines:
Add a Guid field to the Binder object (i.e. the common object shared by multiple objects)
During deserialization, use a static Dictionary and either use an already registered Binder object with the same Guid or add a new Binder object to the static dictionary for others to link against.
I've got my fingers crossed that someone out there has a good understanding of the Microsoft XmlSerializer.
Basically, I have built a system for outputting XML on the back of the serializer which is now causing me a lot of hassle and I am trying to avoid a significant re-write.
Introduction
My current system employs a lot of derived classes.
For example,
BaseResponse -> CarParkResponse -> CarParkResponseInherited
BaseResponse and CarParkResponse (both in a library dll) are seperate from CarParkResponseInherited.
As a result, the base classes are ignorent of the derived class.
What I have done
-> Declared derived classes
I appreciate that in order for xmlserializer to do its thing, there are a number of ways to declare dervied classes.
Declare derived classes in base classes using XmlInclude
or
Declared types to be serialised and deserialised in xmlSerialiser. For example:
XmlSerializer serializer = new XmlSerializer(typeof(CarParkResponse), new Type[] { typeof(CarParkParameters), typeof(CarParkInformation) });
I have gone with the latter.
What I am trying to do
Because the derived classes are seperate and they share the same properties, what I am trying to do is serialize the dervied class as the subclass.
In other words deserialize CarParkResponseInherited as a CarParkResponse.
In "CarParkResponseInherited" I am using the declaration XmlTypeAttribute("CarParkResponse").
Initially this causes a problem when serialized
Types 'CarParkResponseInherited' and 'CarParkResponse' both use the XML type name, 'CarParkResponse', from namespace ''. Use XML attributes to specify a unique XML name and/or namespace for the type."
as the type is already in use "CarParkResponse" so I've declased XmlType("Response") in "CarParkResponse" to get around this.
The Problem
I am now trying to Deserialize the XML returned but I'm now getting the following problem.
The specified type was not recognized: name='CarParkResponse', namespace='', at OriginalRequest xmlns=''
Frustratingly the CarParkResponse is there. I am wondering if this is down to the fact I've used XmlType("Response") in the class and the serializer doesn't recognise the class as being type of CarParkResponse
So my question is
Basically is it possible to pass a derived class as a sub class and have it deserialized as the subclass using the XmlSerializer?
I have experimented with the xml produced.
For example, if I don't use the Serialization tags (such as XmlType() etc.) anywhere in my code. The xml produced will produce a carparkresponse element with "type" as an attribute.
The value is "CarParkResponseInherited". I have written some code that removes "Inherited" from the value which does allow it to be deserialized.
This approach is obviously not good so I am hoping there is a good way around this.
So...
if there is anyone out there that has had to patience to read through this post and can help or offer advice it would be most appreciated as I am all out of ideas.
Thanks.
It might be possible to do something using the XmlAttributeOverrides class. It's mostly used for specific property overrides, so it may or may not be the best thing for you.
The long way around would be to go ahead and serialize as the inherited class. Then, if the mappings are the same, deserialize the xml into the base class, and then, re-serialize into what you want.
Depending on how much or how little control you have over the assemblies, you could override the serialization on the inherited class so it does it as the base class.
This is not properly a question but something more like a thought I had recently.
I'm taking XmlAttribute to XmlSerialize a class as an example: you can set attributes to a class to choose which properties should be serialized, but the same thing can be done quite easy by implementing a teorical interface IXmlSerializable (it does exist something similar, I don't remember) and by overloading a method "Serialize" for that class which just call Serialize on properties you want to serialize (this.myProp1.Serialize()), same for Deserialize
So what I'm basically saying: isn't Attribute method a bit redundant? (I like it actually, but I don't find it logically different from an interface)
Thanks for any answer, as I've said this is just a thought... hopefully someone will find it interesting
Update 1: Well I explained myself in a wrong way, what I'm asking is "why should I choose attribute instead of an Interface (or opposite)", not exactly this specific case (I took serialization because was the first thing that pop out in my mind), by the way thanks for your answer because they are very interesting
From the comments and downvote, maybe I should highlight my main point here: something that can save me hours of work (per type) and horrible code complexity is very much not redundant, but very, very welcome.
"quite easy"? OK; I'm pretty experienced at serialization, but the implementation for that is not what I call easy. Quite the contrary, in fact.
If you don't want to use attributes, there is an overload for XmlSerializer that allows you to configure it at runtime.
But I shudder whenever I hear "implement IXmlSerializable". The attribute approach is very quick and easy:
[XmlRoot("foo"), XmlType("foo")]
[XmlInclude(typeof(SuperFoo))]
public class Foo {
public string X {get;set;}
[XmlAttribute("y")]
public int? Y {get;set;}
[XmlElement("item")]
public List<string> Items {get;set;}
}
public class SuperFoo : Foo {}
I challenge you to write a robust implementation of IXmlSerializable for that very simple example in under 2 hours... and remember that every line you write is a line you have to maintain.
Well, from the best I can tell, they are logically different.
Implementing IXmlSerializable directly impacts the class itself, because you are adding an interface and one or more methods into the implementation of the class. In essence, You are making your own class directly responsibly for the it's serialization.
However, adding the XmlAttribute attributes does not directly impact the functionality of the class, instead you are just decorating it with attributes so that XmlSerializer can carry out the actual serialization functiohality. In this case, you are deferring the serialization to the XmlSerializer class, and providing just enough metadata about your class for XmlSerializer to do it's work.
This is why I prefer the latter attribute approach. When I'm writing a class, I want it to be serializable, but the last thing I care about is the specifics of the implementation, so I always start with thaqt approach and 99% of the time it works fine with very little work. However, if you did need more fine-grain control over the serialization, the implement the IXmlSerializable interface and write your own serialization code.
The programmatic method of implementing the interface may give a bit more control (and likely more speed), but is harder to create and maintain than the attribute method. I mostly use attributes.
You can select properties to (not) serialize with attributes. Implementation of interface is serialization by code.