Lua: attempt to perform arithmetic on global 'mapfinishes' (a nil value)

Question

I'm trying to set up something in a game that runs off of Lua and this specific local function is triggered when the player finishes the map. Here is the code:

local function setDrRanks( ply )
    local name = SQLStr( ply:Nick() )
    local sid = ply:SteamID()

    drsql:query( "SELECT MapFinishes from dr_exp WHERE SteamID = '"..sid.."'", function( q, data )
        local row = data[1]

        if ( row ) then
            mapfinishes = row["Mapfinishes"]
        end

        drsql:query( "REPLACE into dr_exp (`SteamID`, `PlayerName`, `MapFinishes`) VALUES('"..sid.."', "..name..", '"..(mapfinishes+1).."');" );
    end )
end

The function is to insert into SQL via a lua function, which it did successfully when ran the first time, as the player was at 0 finishes. Once they hit 1, it refused to do a simple +1 on the mapfinishes value. Which strange is that this seems to work 100% when the player is at 0 finishes, and it will put them at 1, but once they are at 1, it will not add to it any longer. The error received is:

attempt to perform arithmetic on global 'mapfinishes' (a nil value)

Anyone have any ideas? Thanks in advance.

Answer 1

    local row = data[1]

    if ( row ) then
        mapfinishes = row["Mapfinishes"]
    end

    drsql:query( "REPLACE into dr_exp (`SteamID`, `PlayerName`, `MapFinishes`) VALUES('"..sid.."', "..name..", '"..(mapfinishes+1).."');" )

问题出在表达式mapfinishes+1中，似乎在没有mapfinishes设置的情况下执行了。这意味着上面的if循环没有执行，因为row是nil或false。请记住，在Lua中，零和空字符串是真值。

另一种可能性是row["Mapfinishes"]本身为nil，因此mapfinishes仍为nil。

通常，最小/无全局变量会更好。如果您仅在此功能中使用mapfinishes，则应将其声明为local。