Reading and Writing Tables to Files

[octacian]

What is the easiest way to write, read, and edit tables stored within files? I need to store in a database-like file records of players that are warned or kicked for using inappropriate words in the chat so that the "punishment" is taken to a new level after a certain number of attempts.

I'd also like to use a table/database to store the words that trigger the warning or kick, and to improve the default ban function to work something like xban2.

Speaking of xban2, I tried looking at the code as well as the lua-users wiki but couldn't make sense of anything. If someone can provide me with a detailed explanation of how to read tables from files, as well as write and edit content, I would really appreciate it.

[rubenwardy]

Note that the data you save, in this case awards.players, must not contain any functions or user data (such as player/entity objects or itemstacks)

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Code: Select all

function awards.save()
   local file = io.open(minetest.get_worldpath().."/awards.txt", "w")
   if file then
      file:write(minetest.serialize(awards.players))
      file:close()
   end
end

function awards.load()
   local file = io.open(minetest.get_worldpath().."/awards.txt", "r")
   if file then
      local table = minetest.deserialize(file:read("*all"))
      if type(table) == "table" then
         return table
      end
   end
   return {}
end


[octacian]

Thanks!

If I want to remove an entry, I assume I just set it to nil?

Any good resources on tables? I have basic understanding, and I'm sure I'll find something, however, if you know a worthwhile resource that would be great.

[rubenwardy]

Yes, setting to nil will delete it.

Read this: https://www.lua.org/pil/2.5.html

[octacian]

I tried a method much like the one you showed, but I don't seem to get the return table properly.

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Code: Select all

-- write table to file
function servertools.write_table(path, table)
  local table = minetest.serialize(table) -- serialize table
  local f = io.open(path, "w") -- open file for writing
  f:write(table) -- write table
  f:close() -- close file
  servertools.log("Wrote table to "..path)
end

-- load table from file
function servertools.load_table(path)
  local f = io.open(path, "r") -- open file for reading
  local table = f:read()
  f:close() -- close file
  return table
end

my_table = { foo = "bar" }

st.log("beginning file creation")
servertools.create_file(st.modpath.."/my_table")
servertools.write_table(st.modpath.."/my_table", my_table)
servertools.load_table(st.modpath.."/my_table")
st.log("file creation done and file read")


st.log("Original Table: "..my_table.foo)
if table then st.log("table detected: "..table.foo) end

After loading the table, if I try to print table.foo, I get nil. However, if I print my_table.foo I get bar. Somehow it doesn't seem as though the table is being returned properly, but I'm not sure why.

[Byakuren]

I tried a method much like the one you showed, but I don't seem to get the return table properly.

Your phone or window isn't wide enough to display the code box. If it's a phone, try rotating it to landscape mode.

Code: Select all

-- write table to file
function servertools.write_table(path, table)
  local table = minetest.serialize(table) -- serialize table
  local f = io.open(path, "w") -- open file for writing
  f:write(table) -- write table
  f:close() -- close file
  servertools.log("Wrote table to "..path)
end

-- load table from file
function servertools.load_table(path)
  local f = io.open(path, "r") -- open file for reading
  local table = f:read()
  f:close() -- close file
  return table
end

my_table = { foo = "bar" }

st.log("beginning file creation")
servertools.create_file(st.modpath.."/my_table")
servertools.write_table(st.modpath.."/my_table", my_table)
servertools.load_table(st.modpath.."/my_table")
st.log("file creation done and file read")


st.log("Original Table: "..my_table.foo)
if table then st.log("table detected: "..table.foo) end

After loading the table, if I try to print table.foo, I get nil. However, if I print my_table.foo I get bar. Somehow it doesn't seem as though the table is being returned properly, but I'm not sure why.

A couple issues:

• server_tools.load_table returns the serialized table, rather than the actual table. You need to deserialize it first.
• table (on the printing line) isn't defined in this code snippet, but I'll assume you defined it earlier since you said "nil" gets printed out rather than nothing.
• table is never assigned to the table read from the file. When you call server_tools.load_table, you never assign the result to anything.

[octacian]

Whoops, the load file code was an older version.

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Code: Select all

-- load table from file
function servertools.load_table(path)
  local f = io.open(path, "r") -- open file for reading
  local table = minetest.deserialize(f:read()) -- deserialize and read table
  f:close() -- close file
  return table
end

That should take care of serialization issues. When servertools.load_table is called, I thought I assigned and returned the result through table, in turn defined by:

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Code: Select all

local table = minetest.deserialize(f:read()) -- deserialize and read table
...
return table


[Byakuren]

That's a local definition and is only available in its enclosing scope (the body of load_table). You should assign the result of load_table to a new local variable, somewhere it will be in scope when you use it (changing servertools.load_table(st.modpath.."/my_table") to local table = servertools.load_table(st.modpath.."/my_table") would work fine).

Also you might want to avoid using the variable name "table", even locally, since you won't be able to access the table module which is a global table also called "table". If you don't use the table libraries in you own code though, it doesn't matter too much, but might be confusing if someone reading your code mistakes your local "table" for the global "table".

Setting the global "table" variable will ruin it for everyone who uses the table library though, and in general you should avoid setting global variables other than one with the same name as your mod (usually a table containing things you want to expose publically).