Function return data from DB

[Nikolay_888]

Hello. I create a function, that return data from database.

function takePlayerDataFromDB (id, data) 
    if id and data then 
        local receivedData = false 
        local query1 = dbQuery (function (query)  
            local poll, num_rows = dbPoll (query, 0) 
            if poll then 
                if num_rows == 1 then 
                    for _, row in pairs ( poll ) do 
                        receivedData = row[data] 
                    end 
                end 
            end 
        end, players_db, "SELECT ?? FROM players WHERE id=?", data, id) 
        return receivedData 
    end 
end 
  
a =  takePlayerDataFromDB (5, 'name') 
  

The problem is line 14 runs faster then line 9, and function returns false. And I don't know how to use 'return' right in callback function.

I would be grateful for help.

[JR10]

You need coroutines in order to do that.

Some tutorials: http://www.lua.org/pil/9.html

http://lua-users.org/wiki/CoroutinesTutorial

If you're still a beginner or you couldn't understand what coroutines are then I'd suggest you find a different way to do what you're doing.

[Noki]

db = dbConnect(args) 
  
function getDataFromDb(id, column) 
    if id and column then 
        qh = dbQuery(db, "SELECT `??` FROM `players` WHERE `id`=?", column, id) 
        return dbPoll(qh, 0) 
    end 
end 

Why not use something like that, then loop through the table to get your needed data?

[Nikolay_888]

Noki, i read that using dbQuery without callback function will freeze server.

I searched this topic viewtopic.php?f=91&t=86184&p=780099&hilit=coroutine#p780099

This is the same situation, but I can't use this code for my situation yet.

[Noki]

dbQuery does not freeze the server in the way you think it does. It's more so saying that you won't be able to query the database while the result is being fetched. Your server will still work fine. Correct me if I'm wrong.

Try it yourself.

[JR10]

@Noki Because the data can be not ready yet to be returned. And using -1 instead of 0 will freeze everything until it is returned.

[Nikolay_888]

Oh, I did it. Thank you very much, JR10. This is my code. It works, but is this code right? I used coroutines first time and try 1000 variants

function someFunction () 
   playerco = coroutine.create(function (data) 
      outputChatBox (data, root) 
   end) 
                         
   coroutine.resume (getdataco, 57, 'name') 
end 
  
--- 
getdataco = coroutine.create (function (id, dataDB) 
   local data = false 
     
   function querrrry () 
      local query1 = dbQuery (function (query)  
         local poll, num_rows = dbPoll (query, 0) 
         if poll then 
            if num_rows == 1 then 
               for _, row in pairs ( poll ) do 
                  data = row[dataDB] 
                  coroutine.resume (getdataco) 
               end 
            end 
         end 
      end, players_db, "SELECT ?? FROM players WHERE id=?", dataDB, id) 
   end 
  
   querrrry () 
   coroutine.yield () 
   coroutine.resume (playerco, data) 
end) 

[JR10]

Why are you declaring another function inside the coroutine function? And why do you need 2 coroutines?

Something like this should do:

local co = coroutine.create(function() 
 dbQuery(callback, database, 'SELECT * FROM `table`') 
 local results = coroutine.yield() -- Pause execution until coroutine.resume is called 
 -- use results 
end) 
coroutine.resume(co) -- Start running the coroutine function for the first time 
  
function callback(qh) 
 local results = dbPoll(qh, 0) 
 coroutine.resume(co, results) 
end 

[Nikolay_888]

Function someFunction shows using getdataco in real situation. That is getdataco possible use in another situations.

So, first coroutine need to use received data after receive.

[JR10]

Well, for your problem, my code would just do for you.