Append data in a json file in C#

Question

How would i keep appending data? I have this:

{
  "13232": [
    "2012952"
  ]
}

And i want to add an another object to it, example:

{
  "13232": [
    "2012952"
  ],
  "19213": [
    "2016086"
  ]
}

This is the code i use:

JArray array = new JArray();
array.Add(Itemid);

JObject o = new JObject();
o[Userid] = array;

string json = o.ToString(Formatting.Indented);
//i know this keeps appending text but how would i append it inside the { and }?
File.AppendAllText("E:/media.json", json);

I literally have no idea how to keep adding it, but maybe someone else has?

Answer 1

You won't be able to use file append operations to do this. File append operations can only add text to the end, they can't insert text at some point in the middle. This makes it impossible to use file-append to keep the JSON valid.

You have two choices that I can think of:

1. Read the entire file into an object, add your object, and then rewrite the entire file (poor performance)
2. Open the file read/write, parse through until you get to the closing curly brace, then write the remaining data, then write the close curly brace (not trivial)

Answer 2

The safest approach is read-update-rewrite (applies to JSON and XML format as they don't support appending).

Next option if you can live with invalid JSON is to simply concatenate JSON fragments with code you have and than use SupportMultipleContent in JsonReader to read fragments Read Multiple Fragments With JsonReader

If those approaches don't work and your format is fixed - find position of last ] in the file, seek stream there and write new array elements and append ]}.