continuous serialization of a list with JSON.NET

Question

I am trying to serialize a List to a file in C# with JSON.NET. I want to be able to add values to the list and serialize that change.

I do not want to serialize the list all over again, since it can grow pretty big.

Is something like that possible with JSON.NET?

using (FileStream fs = File.Open(@"c:\list.json", FileMode.CreateNew))
using (StreamWriter sw = new StreamWriter(fs))
using (JsonWriter jw = new JsonTextWriter(sw))
{
    jw.Formatting = Formatting.Indented;

    JsonSerializer serializer = new JsonSerializer();
    serializer.Serialize(jw, list);
}

this way it would only be possible to "Reserialize" the whole list, not add changes to the file.

Answer 1

In many formats (including json and xml), there is semantic closing of the document at the end; to "append" would require back-tracking through this. In others, there may be length-prefix data much earlier in the file that requires changing. In either event, this will only work reasonably if the list is the last (or only) thing in the file - not a safe assumption in the general case, so serializers don't generally include support for "append at the end" after the fact.

My default answer here, therefore, would be:

either reserialize the entire list, or construct some mechanism of "framing" that allows you to store (and subsequently merge) multiple completely independent fragments (without mutating / extending - just add an extra frame)

Note that some formats do support append; for example, protocol buffers deliberately includes no document closing / length preamble - it is a specific feature of the design that append fragment === merge, which for lists means: add an item. However, this is then not json.