error in json in corona lua - json

Question

hi i have found a tutorial on how to use post json in lua.
here is the code :
http = require("socket.http")
crypto = require("crypto")
ltn12 = require("ltn12")
url = require("socket.url")
local json = require("json")
local commands_json =
{
["message"] = "Hello",
}
print (commands_json)
local json = {}
json.api_key = "6_192116334"
json.ver = 1
json.commands_json = json.encode(commands_json)
json.commands_hash = crypto.digest(crypto.md5, json.commands_json .. 'hkjhkjhkjh')
local post = "api=" .. url.escape(Json.Encode(json))
local response = {}
local r, c, h = http.request {
url = "http://127.0.0.1/?page=api",
method = "POST",
headers = {
["content-length"] = #post,
["Content-Type"] = "application/x-www-form-urlencoded"
},
source = ltn12.source.string(post),
sink = ltn12.sink.table(response)
}
local path = system.pathForFile("r.txt", system.DocumentsDirectory)
local file = io.open (path, "w")
file:write (Json.Encode(json) .. "\n")
file:write (post .. "\n")
file:write (response[1] .. "\n")
io.close (file)
json = Json.Decode(table.concat(response,''))
native.showAlert("hey", json.commands[1].tot_nbr_rows)
now i got these error:
Windows simulator build date: Dec 9 2011 # 14:01:29
Copyright (C) 2009-2011 A n s c a , I n c .
Version: 2.0.0
Build: 2011.704
table: 0346D6D0
Runtime error
...nistrator\my documents\corona projects\json\main.lua:17: attempt to c
all field 'encode' (a nil value)
stack traceback:
[C]: in function 'encode'
...nistrator\my documents\corona projects\json\main.lua:17: in main chun
k
Runtime error: ...nistrator\my documents\corona projects\json\main.lua:17: attem
pt to call field 'encode' (a nil value)
stack traceback:
[C]: in function 'encode'
...nistrator\my documents\corona projects\json\main.lua:17: in main chun
k
i don't know why i got the error from encode.
can anyone can help me about my case?
thanks in advance ...

Answer 1

This includes the Json code provided externally, likely with an encode function:
local json = require("json")
This throws away your old json variable and replaces it with an empty table:
local json = {}
And this tries to call json.encode which is now undefined since you redefined json as an empty table above:
json.commands_json = json.encode(commands_json)
The solution is to pick a different variable name.