Updating Json files in a Unity game - What am I doing wrong?

Question

I am working in Unity, on my first project. I am working on a turn-based RPG, and I am having a hard time figuring out my back end.

I'm currently using JSON files to store my data, which are then converted into objects and processed in C#. So far so good, but I have reached a road block when trying to save data back into a JSON file.

For example, lets say I have a character file such as: [{"name":"John", "CurrentHP": 100, "MaxHP": 100},{"name":"Paul", "CurrentHP": 200, "MaxHP": 200}]. After a combat, John loses 30 hp. How do I save this data back to that JSON file, so it reads as [{"name":"John", "CurrentHP": 70, "MaxHP": 100},{"name":"Paul", "CurrentHP": 200, "MaxHP": 200}]?

The tutorials I've watched all talk about serializing the object back into a JSON file, but this would involve deleting the whole file and creating a new one with the new information. This sounds like a very ineffective approach, especially for some large 'tables' in my game. There needs to be a way to update just one attribute from one of the IDs in a given JSON file.

How do I efficiently update individual JSON rows?

Answer 1

JSON is a string-based format. When you change the length of something in a JSON file (for example by changing "CurrentHP": 99 to "CurrentHP": 101 everything which comes after that in the JSON file needs to be rewritten because it's now at the wrong offset. That's how string-based file formats work. For that reason JSON libraries rarely support in-place replacement of individual fields, and Unity is no exception.

To mitigate the problem you might want to avoid too large JSON files. Split information into multiple files instead. For example, when you have a large table of objects, make each row an individual file. There is no law which says each savegame must be a single file and can not be a directory of multiple files.

Alternatively, you could use a proper database. Like SQLite, for example.

You should also avoid unnecessary saving. You generally don't need to save the complete gamestate whenever anything in the game changes. It is completely adequate to save when the player tells you to and/or autosave at regular checkpoints.

Answer 2

Make two files, GameData.json for storing actual data and GameState.json for holding the the current state. When your character initialized first time, assign their stats from GameData. When saving state of your character, write on GameState. SO next time when your character load, get state from GameState.