lua - 如何使用 luasql 将函数输出添加到变量

Question

我正在尝试将函数的输出分配给变量，但我做不到。:(

我使用Lua 5.3.4和luarocks 3.2.1 (+ luasql-postgres )

我的脚本：

luasql = require "luasql.postgres"
value=arg[1]
current_time=os.date("%Y-%m-%d %H:%M:%S")
env = luasql.postgres()
con = assert (env:connect('postgres', 'postgres', 'postgres', '192.168.241.93','5432'))

function printvalues(res)
    row = res:fetch ({}, "a")
    while row do
            print(string.format("%-12s", row.client_addr))
            row = res:fetch (row, "a")
    end
    print()
end

res = assert (con:execute('select client_addr from pg_stat_replication order by replay_lag asc limit 1'))


--txn = res
a = {myfunc = printvalues(res)}

if a == '192.168.242.41' then
print("backend1")
elseif a == '192.168.241.76' then
print("backend2")
end

print(string.format("%-12s",a))
print(a)

脚本结果：

root@haproxy:/etc/haproxy# lua scripts/test.lua
192.168.1.76

table: 0x559fadf97080
table: 0x559fadf97080

请告诉我：

1. 如何将函数的结果分配给变量？

2. 如何删除函数printvalues(res)输出中的空行

Answer 1

1. 需要return在函数体中声明返回值
2. 您示例中的空行是print()函数中的语句printvalues

我看到您正在使用 进行查询limit 1，因为您只会得到一个值，因此while循环语句是无用的。

我希望这对你有用

local luasql = require "luasql.postgres"
local env = luasql.postgres()
local con = assert (env:connect(
  'postgres', 'postgres', 'postgres', '192.168.241.93', '5432'
))
local res = assert(con:execute(
  'select client_addr from pg_stat_replication order by replay_lag asc limit 1'
))
local row = res:fetch({}, 'a')
local a = string.format('%-12s', row.client_addr)

res:close()

if a == '192.168.242.41' then
  print('backend1')
elseif a == '192.168.241.76' then
  print('backend2')
end

print(a)

但是如果你想要一个函数的例子：

local luasql = require "luasql.postgres"
local env = luasql.postgres()
local con = assert (env:connect(
  'postgres', 'postgres', 'postgres', '192.168.241.93', '5432'
))
local res = assert(con:execute(
  'select client_addr from pg_stat_replication order by replay_lag asc limit 1'
))

local function printvalues(res)
  local row = res:fetch({}, 'a')
  res:close()
  return string.format('%-12s', row.client_addr)
end

local a = printvalues(res)

if a == '192.168.242.41' then
  print('backend1')
elseif a == '192.168.241.76' then
  print('backend2')
end

print(a)

尝试local在变量之前使用关键字，这将使它们成为范围变量

Answer 2

感谢。我最终使用了这个脚本：

luasql = require "luasql.postgres"
env = luasql.postgres()
con = assert (env:connect('postgres', 'postgres', 'postgres','333.333.333.333','5432')) --master

backend = function(txn)
res = assert (con:execute('select client_addr from pg_stat_replication order by replay_lag asc limit 1'))
row = res:fetch ({}, "a")
while row do
    ip = string.format("%-12s", row.client_addr)
    row = res:fetch (row, "a")
end
result = "backend1"
if ip == '111.111.111.111' then
result = "backend1"
elseif ip == '222.222.222.222' then
result = "backend2"
end
return result
end

core.register_fetches("choose_backend", backend)