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C# Object Serialization Changes

I have the following issue:
My object is being serialized as follows:
MemoryStream memorystream = new MemoryStream();
BinaryFormatter bf = new BinaryFormatter();
bf.Serialize(memorystream, _policy);
CaptureData = Convert.ToBase64String(memorystream.ToArray());
And then saved to my database and de-serialized as required from the data saved in the database.
My problem now is that I can't make changes to this object, add properties etc as this breaks the deserialization.
Any suggestions on how I can add properties without breaking serialization of previous objects?

I don't think it's possible using this serializer.
If possible, use another serializer that deals with backward compatibility like protocol buffers

You can use [OptionalField] and similar to take advantage of the version tolerant serialisation built into .Net.

You need to shift from the built-in serialization , as this is, as you saw, is rigid and not scallable. Pick any other serializaiton technique that let's you maintan scallability of your types and flexibility of your system.
custom binary serialization
xml serialization
json serialization
binary serialization with protobuf (just example...)
All this, if you can do that. If not, for some architectural (historical) restrictions, just can do something like suggested in Hamlet's comment. But it sounds like a rough solution to me.

Generic serializer with ProtoBuf.net

I'm attempting to write a generic serializer using protobuf.net v2. However I'm running into some issues which make me wonder if perhaps what I'm doing is impossible. The objects to be serialized are of an indeterminate type to which I don't have access so I'm attempting to walk the object and add its properties to the type model.
var model = TypeModel.Create();
List<string> propertiesToSerialize = new List<string>();
foreach (var property in typeToSerialize.GetProperties())
{
propertiesToSerialize.Add(property.Name);
}
model.AutoAddMissingTypes = true;
model.Add(typeToSerialize, true).Add(propertiesToSerialize.ToArray());
For simple objects which contain only primitives this seems to work just fine. However when working with an object which contains, say, a Dictionary<string,object> I encounter an error telling me that no serializer is registered for Object.
I did look at serializing a Dictionary<string,object> in ProtoBuf-net fails but it seems the suggested solution requires some knowledge and access to the object being serialized.
Any suggestions on how I might proceed?

protobuf-net does not set out to be able to serialize every scenario (especially those dominated by object), in exactly the same way that XmlSerializer and DataContractSerializer have scenarios which they can't model. In particular, the total lack of metadata in the protobuf format (part of why it is very efficient) means that it is only intended to be consumed by code that knows the structure of the data in advance - which is not possible if too much is object.
That said, there is some support via DynamicType=true, but that would not currently be enabled for the dictionary scenario you mention.
In most cases, though, it isn't really the case that the data can be anything; more typically there are a finite number of expected data types. When that is the case, the object problem can be addressed in a cleaner way using a slightly different model (specifically, a non-generic base-type, a generic sub-type, and a few "include" options). As with most serialization, there are scenarios were it may be desirable to have a separate "DTO" model, that looks closer to the serialization output than to your domain model.
A final note: the GetProperties()/Add() approach is not robust, as GetProperties() does not guarantee any particular order to the members; with protobuf-net in the way you show, order is important, as this helps determine the keys to use. Even if the order was fixed (sorting alphabetically, for example), note that adding a member could be a breaking change.

How to dynamically create a JSON object in c# (from an ASP.NET resource file)?

I need to serialize the strings from a resource file (.resx) into a JSON object. The resource file's keys are in flux and thus I cannot just create a C# object that accepts the appropriate values. It needs to be a dynamic solution. I am able to loop through the key-value pairs for the file, but I need an easy way to serialize them to JSON.
I know I could do:
Object thing = new {stringOne = StringResource.stringOne; ...}
But, I'd rather have something like:
Object generic = {}
foreach (DictionaryEntry entry in StringResource) {
generic.(entry.Key) = entry.Value
}
Or should I just create a custom JSON serializer that constructs the object piecemeal (i.e. foreach loop that appends part of the JSON string with each cycle)?
EDIT
I ended up writing a quick JSON serializer that constructs the string one field at a time. I didn't want to include a whole JSON library as this is the only use of JSON objects (for now at least). Ultimately, what I wanted is probably impractical and doesn't exist as it's function is better served by other data structures. Thanks for all the answers though!

If you're using C# 4.0, you should look at the magical System.Dynamic.ExpandoObject. It's an object that allows you to dynamically add and remove properties at runtime, using the new DLR in .NET 4.0. Here is a good example use for the ExpandoObject.
Once you have your fully populated ExpandoObject, you can probably easily serialize that with any of the JSON libraries mentioned by the other excellent answers.

This sounds like an accident waiting to happen (i.e. creating output prior to cementing the structure), but it happens.
The custom JSON serializer is a compelling option, as it allows you to easily move from your dictionary into a JSON format. I would look at open source libraries (JSON.NET, etc) to see if you can reduce the development time.
I also think setting up in a slightly more structured format, like XML, is a decent choice. It is quite easy to serialize from XML to JSON using existing libraries, so you avoid heavy customization/
The bigger question is what purposes will the data ultimately serve. If you solve this problem using either of these methods, are you creating bigger problems in the future.

Probably I would use JSON.NET and the ability to create JSON from XML.
Then, you could create an XML in-memory and let JSON.NET convert it to JSON for you. Maybe if you dig deeper into the API, there are other options, too.

Newtonsoft is a library that has all kinds of nifty JSON tools...among them, on-the-fly one-line serializer and deserializers...check it out, it's my favorite JSON library out there
http://james.newtonking.com/pages/json-net.aspx
If I remember correctly, it has a class that will convert JSON to a .NET object without having to create the .NET object first. Think it is in the Json.Convert class

The way I do it is:
var serialiser = new System.Web.Script.Serialization.JavaScriptSerializer();
string json = serialiser.Serialize(data);
context.Response.Write(json);

Slightly non-trivial data structure: is XmlSerializer right for me?

I'm currently using XmlSerializer to, surprisingly enough :), handle de/serialization of my data structures - I find it wonderfully simple to use, but at the cost of flexibility. At the moment, I'm using it for a tree-based structure; since XmlSerializer doesn't handle cyclic structures, I've added [XmlIgnore] to my Parent property, and do a post-deserialization iteration over the tree to fix up node parents.
Is there a better way to handle this using XmlSerializer, or would it be better to rewrite the code using XmlReader/XmlWriter? I suppose implementing IXmlSerializable would work, but it seems like a fair amount of work, while still retaining the cons of XmlSerializer.
The current post-deserialization step is OK, but I'm adding a data structure that has to be serialized to a separate XML file: basically a flat list of items that need a Parent property referencing a node from the previous tree structure. This would require yet a post-deserialization step, as well as keeping both a Parent attribute as well as as ParentId (or some trickery) in the new data structure.
So, any smart (and non-fragile) ideas? Or XmlReader/XmlWriter it is?
Solution
DataContractSerializer turned out to be a pretty decent solution, with pretty much the same simplicity as XmlSerializer. I opted not to use the automatic cycle handling but instead defining and OnDeserialized decorated method to handle setting the parent node; that way, the generated XML is standard-conforming.
One thing that confused me for a while was that I got crashes on some properties after deserializing, with the backing members set to null - couldn't figure out how this was possible since the backing members were definitely initialized in all possible constructors. Debugging showed constructors were never called, and after some googling I found this SO post with an explanation.

You could try binary serialization (BinarySerializer or DataContractSerializer), which I think handles cyclic graphs somewhat better, at the cost of not having a human-readable representation of the data. Alternatively, you can try the SoapFormatter as detailed here.

Use DataContractSerializer. Mark your classes with [DataContract(IsReference = true)].

How to design to prompt users for new values for properties of deserialized objects?

Right now, I'm currently serializing a class like this:
class Session
{
String setting1;
String setting2;
...etc... (other member variables)
List<SessionAction> actionsPerformed;
}
Where SessionAction is an interface that just has one method. All implementations of the SessionAction interface have various properties describing what that specific SessionAction does.
Currently, I serialize this to a file which can be loaded again using the default .Net binary serializer. Now, I want to serialize this to a template. This template will just be the List of SessionActions serialized to a file, but upon loading it back into memory at another time, I want some properties of these SessionActions to require input from the user (which I plan to dynamically generate GUI controls on the fly depending on the property type). Right now, I'm stuck on determining the best way to do this.
Is there some way I could flag some properties so that upon using reflection, I could determine which properties need input from user? Or what are my other options? Feel free to leave comments if anything isn't clear.

For info, I don't recommend using BinaryFormatter for anything that you are storing long-term; it is very brittle between versions. It is fine for short-lived messages where you know the same version will be used for serialization and deserialization.
I would recommend any of: XmlSerializer, DataContractSerializer (3.0), or for fast binary, protobuf-net; all of these are contract-based, so much more version tolerant.
Re the question; you could use things like Nullable<T> for value-types, and null for strings etc - and ask for input for those that are null? There are other routes involving things like the ShouldSerialize* pattern, but this might upset the serialization APIs.

If you know from start what properties will have that SessionAction, you must implement IDeserializationCallback and put to those props the attribute [NonSerialized]. When you implement the OnDeserialization method you get the new values from the user.