How can I detect changes in nested table and get the location of the key?

Help and Feedback Scripting Support
1

Right now I have this code that detects changes in a table, however, I need to know the key’s exact location, how can I do that?

local function Proxify(currentTable: {any})
	local proxy = newproxy(true)
	local meta = getmetatable(proxy)

	meta.__index = function(self, key)
		local idx = currentTable[key]
		if idx and type(idx) == "table" then
			idx = Proxify(idx)
		end
		return idx
	end

	meta.__newindex = function(self, key, value) -- THIS KEY
		if currentTable[key] ~= value then
			currentTable[key] = value
			print("Change made in ", key, " = ", value)
		end
	end

	return proxy
end

For example if I do this:

local data = Proxify({ store = { coins = 50 } })
data.store.coins = 100

I want to get "data.store.coins" as location of the key that changed.

2

‘self’ is a reference to the table that you either attempted to query or you attempted to assign to.

print(self.coins) --50
3

Yes, but I am asking on how I can listen for changes in a table.

If I use newproxy, it will create userdata object which won’t work with table.insert.
If I don’t use newproxy, there will be still a problem since table.insert won’t trigger changes because it’s using rawset.
Comparing tables every frame would be my best option but that would be inefficient.

4 
local Proxy = {}

local Table = setmetatable({}, {
	__index = function(Self, Key)
		return Proxy[Key]
	end,
	
	__newindex = function(Self, Key, Value)
		print("Value of table changed!")
		Proxy[Key] = Value
	end,
})

Table.Message = "Hello world!"
Table.Message = "Test!"

Notice how the print command is ran twice even though the same table key is assigned.

5

Yes, but now try to use table.insert, it won’t fire.

6

So don’t use table.insert? You have full control over your own programming.

7

The problem is that I want to use it.

8

Array[#Array + 1] = "Value"

Emulate table.insert instead, granted this is just emulating its default behavior.

1 Like
9 
local function insert(t, v, p)
    if not p then p = #t+1 end
    for i = #t, p, -1 do
        t[i+1] = t[i]
    end
    t[p] = v
end

This should only be used if you want to shift all of the values. Otherwise use what Forummer said.

1 Like
10

It doesn’t work on nested tables.

function TrackTable()
	local currentRaw = {}
	
	return setmetatable({}, {
		__index = function(self, key)
			return currentRaw[key]
		end;
		
		__newindex = function(self, key, value)
			print("Changed")
			currentRaw[key] = value
		end;
	})
end

local tbl = TrackTable()

tbl.Inventory = {
	Codes = {
		"Summer2020"
	}
}

tbl.Inventory.Codes[#tbl.Inventory.Codes + 1] = "Summer2022"