minetest_modding_book/chapters/node_metadata.md

title	layout	root
Node Metadata	default	../

Introduction

In this chapter you will learn how to manipulate a node's metadata.

• What is Node Metadata?
• Getting a Metadata Object
• Reading Metadata
• Setting Metadata
• Lua Tables
• Infotext
• Your Turn

What is Node Metadata?

Metadata is data about data. So Node Metadata is data about a node.

You may use metadata to store:

• an node's inventory (such as in a chest).
• progress on crafting (such as in a furnace).
• who owns the node (such as in a locked chest).

The node's type, light levels, and orientation are not stored in the metadata, but rather are part of the data itself.

Metadata is stored in a key value relationship.

Key	Value
foo	bar
owner	player1
counter	5

Getting a Metadata Object

Once you have a position of a node, you can do this:

{% highlight lua %} local meta = minetest.get_meta(pos) -- where pos = { x = 1, y = 5, z = 7 } {% endhighlight %}

Reading Metadata

{% highlight lua %} local value = meta:get_string("key")

if value then print(value) else -- value == nil -- metadata of key "key" does not exist print(value) end {% endhighlight %}

Here are all the get functions you can use, as of writing:

• get_string
• get_int
• get_float
• get_inventory

In order to do booleans, you should use get_string and minetest.is_yes:

{% highlight lua %} local value = minetest.is_yes(meta:get_string("key"))

if value then print("is yes") else print("is no") end {% endhighlight %}

Setting Metadata

Setting meta data works pretty much exactly the same way.

{% highlight lua %} local value = "one" meta:set_string("key", value)

meta:set_string("foo", "bar") {% endhighlight %}

Here are all the set functions you can use, as of writing:

• set_string
• set_int
• set_float

Lua Tables

You can convert to and from lua tables using to_table and from_table:

{% highlight lua %} local tmp = meta:to_table() tmp.foo = "bar" meta:from_table(tmp) {% endhighlight %}

Infotext

The Minetest Engine reads the field infotext in order to make text appear on mouse-over. This is used by furnaces to show progress and signs to show their text.

{% highlight lua %} meta:set_string("infotext", "Here is some text that will appear on mouse over!") {% endhighlight %}

Your Turn

• Make a block which disappears after it has been punched 5 times. (use on_punch in the node def and minetest.set_node)