Module:Cache

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This module provides a way of storing data between module invocations. Possible data types are strings, numbers, nil and tables. This is useful for templates that tend to appear multiple times on the same page. Do not use this for modules that only appear a single time per page. It will lead to performance decreases.

Warning[edit]

Metatables are not preserved. To work around this, this module automatically checks for a __tostring method and converts the table to a string if possible.

Functions[edit]

Basic[edit]

cache.auto[edit]

cache.auto(func, args, prefix)

The cache.auto function is the simplest way of implementing caching. It wraps the function supplying the value and automatically decides whether to execute the function or use a cached version.


It's parameters are:

  1. The function for which caching should be applied.
  2. A table holding the functions arguments.
  3. An optional prefix for the key under which the output will be stored (useful if multiple functions have the same arguments).

In pseudo-code it would look something like this:

function cache.auto(func, args, prefix)
  if prefix_args[1]_args[2].isCached() then
    return get_cache(prefix_args[1]_args[2])
  else
    return set_cache(prefix_args[1]_args[2], func(args))
  end
end

Advanced[edit]

Use these functions if you want to manually implement caching in your module.

cache.set[edit]

cache.set(args, value, prefix)

Stores content. Logs the stored content and the variable name. Returns the content.

cache.get[edit]

cache.get(args, prefix)

Retrieves content. Returns the content.

Usage[edit]

local p = {}
local cache = require('Module:Cache')


function p.example(args)
  -- First usage of p._example(); Executes the function and stores the value.
  cache.auto(p._example, args, 'example_prefix')

  -- Second usage; Uses the cached version.
  cache.auto(p._example, args, 'example_prefix')
end

function p._example(args)
  return args[1]
end


return p

Tests[edit]

YesY All tests passed.

Name Expected Actual
YesY test_auto_boolean
YesY test_auto_number
YesY test_auto_string
YesY test_auto_table
YesY test_get_boolean
YesY test_get_no_set
YesY test_get_number
YesY test_get_string
YesY test_get_table
YesY test_set_boolean
YesY test_set_number
YesY test_set_string
YesY test_set_table

Dependencies

--------------------------------------------------------------------------------
-- Imports
--------------------------------------------------------------------------------

local libraryUtil = require( 'libraryUtil' )
local var = require( 'Module:Variables' ).var
local vardefine = require( 'Module:Variables' ).vardefine

--------------------------------------------------------------------------------
-- Strings
--------------------------------------------------------------------------------

local i18n = {
  error = {
    unsupported_type = 'Unsupported data type'
  },
  log = {
    caching = 'No cached version found. Storing.'
  }
}

--------------------------------------------------------------------------------
-- Helper functions
--------------------------------------------------------------------------------

local h = {}

--- Generate a variable unique key.
-- @param args (table): The template/module arguments.
-- @param prefix (string): A unique prefix for the cached template/module.
-- @return (string): A unique key.
function h.make_key( args, prefix )
  prefix = ( prefix or 'cache' )
  local key = { prefix }
  for _,arg in pairs( args ) do
    key[#key+1] = tostring( arg )
  end
  local key = table.concat( key, '_' )
  return mw.hash.hashValue( 'md5', key )
end

--- Convert a value into a string for caching.
-- @param value (string/number/bool/table/nil): The value to be converted
-- @return (string): The converted value.
-- @return (string): The original type.
function h.preprocess( value )
  local value_type = type( value )
  
  if value_type == 'number' or value_type == 'boolean' then
    value = tostring( value )
  elseif value_type == 'table' then
    -- Check the table for a metatable to detect mw.html and similar objects.
    local mt = getmetatable( value )
    if mt and mt.__tostring then
      value = tostring( value )
      value_type = 'string'
    else
      value = mw.text.jsonEncode( value )
    end
  elseif value_type ~= 'string' then
    error( i18n.error.unsupported_type )
  end

  return value, value_type
end

--- Convert a string value back to its original type.
-- @param value (string): The string value.
-- @param value_type (string): The original type.
-- @return (string/number/bool/table/nil): The value in its original type.
function h.process( value, value_type )
  if value_type == 'string' then
    return value
  elseif value_type == 'number' then
    return tonumber( value )
  elseif value_type == 'boolean' then
    return ( value == 'true' )
  elseif value_type == 'table' then
    return mw.text.jsonDecode( value )
  elseif not value_type then
    return
  else
    error( i18n.error.unsupported_type )
  end
end

--- Write a value to the cache.
-- @param key (string): The key under which the value will be stored.
-- @param value (string/number/bool/table/nil): The value to store.
-- @return (string/number/bool/table/nil): The value.
function h.write( key, value )
  local processed_value, value_type = h.preprocess( value )
  vardefine( key, processed_value )
  vardefine( key .. '__type', value_type )
  return value
end

--- Read a value from the cache.
-- @param key (string): The key from which to retrieve the value.
-- @return (string/number/bool/table/nil): The original value.
function h.read( key )
  local value = var( key )
  local value_type = var( key .. '__type' )

  return h.process( value, value_type )
end

--------------------------------------------------------------------------------
-- Functions
--------------------------------------------------------------------------------

local p = {}

function p.auto( func, args, prefix )
  libraryUtil.checkType( 'auto', 1, func, 'function' )
  libraryUtil.checkType( 'auto', 2, args, 'table' )
  libraryUtil.checkType( 'auto', 3, prefix, 'string', true )

  local key = h.make_key( args, prefix )
  local cached = h.read( key )
  if cached then
    return cached
  else
    mw.log( i18n.log.caching )
    return h.write( key, func( args ) )
  end
end

function p.set( args, value, prefix )
  libraryUtil.checkType( 'set', 1, args, 'table' )
  libraryUtil.checkTypeMulti( 'set', 2, value, { 'boolean', 'string', 'number', 'table' } )
  libraryUtil.checkType( 'set', 3, prefix, 'string', true )

  local key = h.make_key( args, prefix )

  return h.write( key, value )
end

function p.get( args, prefix )
  libraryUtil.checkType( 'get', 2, args, 'table' )
  libraryUtil.checkType( 'get', 3, prefix, 'string', true )

  local key = h.make_key( args, prefix )

  return h.read( key )
end

function p.key( args, prefix )
  return h.make_key( args, prefix )
end

--------------------------------------------------------------------------------
-- Return
--------------------------------------------------------------------------------

return p