I have long held the believe that your domain model should not be responsible for serializing itself to XML. I have used the IXmlSerializable interface in the past to control how my objects are serialized but ideally I'd prefer the nuts and bolts of the serialization to live outside the object.
However I've never been able to actually implement this in a clean manner and I was wondering if there was any patterns I was overlooking to make this happen. Basically I want my object model to do it's thing and be oblivious to XML serialization (or any other serialization for that matter) and then handed off to some service that spiders the object and serializes it.
I've tried doing this with extension methods but this falls short when you want to serialize a collection of type object. I've looked at doing it with object wrappers and DTO's that then serialize but then you've got the overhead of maintaining another set of objects and having to create these objects when you want to serialize which again can get messy when you have collections of type object.
The only other thing is using reflection but I'd worry about the processing overheads.
Is there a sane way to do what I'm asking or should I just bite the bullet and make my objects xml aware?
Using the System.Xml.Serialization Attributes is putting the nuts and bolts outside of your code. You are defining metadata and with the exception of optional parameters, no extra code is required. Implementing IXmlSerializable and doing the serialization by hand is error prone and should be avoided. Why? You are defining your data 3 times.
XML Schema
Class
Serialization code
Using attributes, you can scrub step 3.
XML and C# has an impedance mismatch. Like it or not, at some point, you will need to define the serialization to create the right document model.
Arguably, the classes you are serializing should not be performing any work. They are just a data store. Try abstracting your logic away from serialized objects - it may give you a warmer feeling.
Update
If you really, really hate attributes, try using the adapter pattern to serialize your model. The XML code will be in a separate class or assembly and you can work with your model across storage mediums. You will suffer the consequence of having to update the serialization separately when you update your model.
Related
I am building a C# integration tool, but I am having some trouble figuring out if I should create different classes for the data that I am receiving from different requests from the source application using REST. The responses are similar in a way that the constructs are the same, but for different information. I.e they would have an "Attributes" tag, but the attributes may vary per class. In the same breath, about 60% or more of the attributes are the same.
It looks like they reused the same constructs, but depending on the data, there are may be more things in the result.
My question is, what is the best practice when creating the classes for the JSON Deserialisation? Do you create multiple classes with the same name and same content(diff namespaces), or do you combine the classes into a "Generic" data type and just include the "extra" attributes, even though they wont all be used by one object.
The assumption is that the "null" values will not be considered in the deserialisation. Thus "extra" fields defined will just be ignored if not found.
The problem comes in the Classes where I would like to be able to define DataType1 and DataType2, but when combining the classes this becomes a problem...
Would like to hear your thoughts :)
Rgs,
Francois
Personally I prefer to deserialize in generic classes (lists and dictionaries or whatever your deserialization library offers) and then manually copy the data to whatever further data structures I use internally. Most of the time the "deserialization classes" really are used just for deserialization and the after that the data is immediately copied to further data structures that don't match the deserialization structures. So there's very little value to them.
I have an entity class which can change over period of time. As of now, I binary serialization to serialize an object of this class. But if I add a new property to the class, I can't deserialize a stream serialized earlier. I tried if I can use BSON with json.net.
I need to take care of these things:
Memory footprint of serialized data should be low
serialization and deserialization should be fast
Need to provide backward compatibility for data serialized with old entity class structure
One approach I considered is to convert the object to IDictionary before serializing it so that I can set default value to properties that are not matching while deserializing. While this works well, it involves additional step to convert the object to IDictionary.
Has anyone faced this situation? what are the approaches you use?
Actually binary serialization is very flexible. Of course, you can just add [Serializable] attribute to the class and forget about details, but you can also take the full control on serialization by implementing ISerializable interface/by adding methods/attributes which corresponds to the certain steps of serialization/deserialization lifecycle. Considering your question about structure changes, please take a look on the following article.
I'm trying to create a function that will save the current state of my application to a file, and another function to load a saved file. Currently, all the information is contained within a single object, which in turn refers to other objects. I recently heard that C# has some built-in classes that help you serialize and deserialize your objects, so I did a little research and learned about DataContracts, mostly from this page: http://msdn.microsoft.com/en-us/library/ms731073.aspx
Most of it works, except for the classes that implement built-in classes. For example, I have an object that inherits System.Windows.DependencyObject, and when I try to serialize it, it complains that my class inherits a class that does not have the DataContract attribute.
It makes sense to me why that would be a problem. When an object is being deserialized, its constructor is not called. If it inherits something that is not serializable, that might leave it in an invalid state.
I was wondering if this was possible: can I somehow tell the deserializer to call the base class's default constructor before deserializing my object? And then I would have to tell the serializer not to freak out.
Can you create a data transer object that has all the properties you want to store, then populate that object with data from the framework object? Mark it as serialized, fire up the serialization class of your choice - and now you have all the info you need. You just need to re-populate the appropriate class after deserialization.
You may want to look into using a binary serializer or xml serializer instead of a data contract serializer for this one. If you're saving it to a file and don't need the file human-readable binary serialization nearly always works.
See Binary Serialization, and in particular the Basic Serialization topic.
Also take a look at the XmlSerializer Class which will sometimes work where a DataContractSerializer doesn't.
It's ok if the answer to this is "it's impossible." I won't be upset. But I'm wondering, in making a game using C#, if there's any way to mimic the functionality of the "save state" feature of console emulators. From what I understand, emulators have it somewhat easy, they just dump the entire contents of the virtualized memory, instruction pointers and all. So they can resume exactly the same way, in the exact same spot in the game code as before. I know I won't be able to resume from the same line of code, but is there any way I can maintain the entire state of the game without manually saving every single variable? I'd like a way that doesn't need to be extended or modified every single time I add something to my game.
I'm guessing that if there is any possible way to do this, it would use a p/invoke...
Well, in C# you can do the same, in principle. It's called serialization. Agreed, it's not the exact same thing as a memory dump but comes close enough.
To mark a class as serializable just add the Serializable attribute to it:
[Serializable]
class GameState
Additional information regarding classes that might change:
If new members are added to a serializable class, they can be tagged with the OptionalField attribute to allow previous versions of the object to be deserialized without error. This attribute affects only deserialization, and prevents the runtime from throwing an exception if a member is missing from the serialized stream. A member can also be marked with the NonSerialized attribute to indicate that it should not be serialized. This will allow the details of those members to be kept secret.
To modify the default deserialization (for example, to automatically initialize a member marked NonSerialized), the class must implement the IDeserializationCallback interface and define the IDeserializationCallback.OnDeserialization method.
Objects may be serialized in binary format for deserialization by other .NET applications. The framework also provides the SoapFormatter and XmlSerializer objects to support serialization in human-readable, cross-platform XML.
—Wikipedia: Serialization, .NET Framework
If you make every single one of your "state" classes Serializable then you can literally serialize the objects to a file. You can then load them all up again from this file when you need to resume.
See ISerializable
I agree with the other posters that making your game state classes Serializable is probably the way you want to go. Others have covered basic serialization; for a high end alternative you could look into NHibernate which will persist objects to a database. You can find some good info on NHibernate at these links:
http://www.codeproject.com/KB/database/Nhibernate_Made_Simple.aspx
http://nhibernate.info/doc/burrow/faq
XML Serialization from MSDN:
Serializes and deserializes objects
into and from XML documents. The
XmlSerializer enables you to control
how objects are encoded into XML.
Reflection from MSDN
Reflection provides objects (of type
Type) that encapsulate assemblies,
modules and types. You can use
reflection to dynamically create an
instance of a type, bind the type to
an existing object, or get the type
from an existing object and invoke its
methods or access its fields and
properties. If you are using
attributes in your code, Reflection
enables you to access them.
As far as my understanding goes, I could create objects in run time using XML Serialization? In other words, let's say I have a database, I could define my "classes" or "objects" in couple of tables. I could then get the XML for the object's data and then create the object at run-time.
I could also already have those objects compiled as libraries readily available and then use Reflection to access it's functions.
From your understanding, which one of these two concepts would grant the most flexibility while sacrificing the least performance? Bonus points if you can provide a detailed explanation with considerations and perhaps a sample of code.
Serialization and Reflection are not mutually exclusive. You could definitely serialize and deserialize an object and then subsequently modify it using Reflection.
Serialization
Serialization is simply the concept of taking a 'snapshot' of an object's state so that you can potentially restore that snapshot at a later time.
If you wish to store objects in a persistent store, serialization is a good option if you don't need to be able to query after particular values.
Note that there are at least two different types of serialization:
XML Serialization, that represents an object as XML. Since it is XML, this representation is (in theory at least) human-readable and interoperable.
Binary serialization, that simply stores and reads an object as an array of bytes. This representation is proprietary and not human-readable.
Reflection
Reflection is the ability to use object metadata to manipulate an object. You could, for example, decide that you want to assign the string "Foo" to all writable string properties of a given object, irrespective of the type of object.
This is mostly interesting when the type of object is not known at design time.
To use deserialize an object you need to know the type you want to deserialize it into. So you can't just create you objects from xml without having its type defined in an assembly.
What you can do is to store xml in your database that represents serialized objects. You could then load the xml from the database and deserialize it into object instances as needed. The source of the xml need not be a serialized object, so you can create it manually if you need.
Using reflection would be a different situation. With reflection you could take an object and get a list of the method and properties available on the object. You could then write code that worked dynamically with your objects regardless of which type they implement. The problem with this approach is that the code is clumsy to write and read, and it is very easy to introduce errors that are only visible at run time. On top of that the code will run slowly due to the overhead introduced by using reflection.
Instead of using reflection I would have my objects implement some well known interfaces that I could cast them to. That would allow my code to be type-safe and I could avoid the hassle of reflection. The code would also run much faster and be more readable.
You cannot create new types on the fly using neither XML serialization nor reflection. These techniques only applies to existing types. If you need to create new types at runtime you will have to use another approach. However, generating types of the fly is of limited usefulness since you can only use reflection to access these types. Using the dynamic runtime in the next major release of .NET will give you more options for creating and using dynamic types.
XML serialization is for serializing objects to and from a well known format (XML). Reflection is much more general and enables you to inspect type information at runtime and manipulate objects without knowing their type at compile time. You can also do serialization using reflection, but it is much more cumbersome compared to XML serialization.