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LUA script for modification object in Redis

I Need a short advise please about LUA script for modification object in Redis.
I Have Redis List with entities like that:

{
  "@class": "com.myproject.model.Book",
  "bookId": "someId",
  "author": "someAuthor"
}

now, I need to change my entity to allow multiple authors for certain book, and create migration script for this:

{
  "@class": "com.myproject.model.Book",
  "bookId": "someId",
  "authors":  [
           "java.util.ArrayList",
            [
              "someAuthor"
            ]
         ]
}

What I Think I need to do with LUA:

local book
local cacheName --cache name in my case
local authorId;

local size = redis.call('LLEN', cacheName)
if size == 0
then
    return -1
end

while size > 0
do
    book = redis.call('LPOP', cacheName)
    
    -- modify entity here 

    affectedEntitiesCount = affectedEntitiesCount + 1
    redis.call('RPUSH', cacheName, book)
    size = size - 1
end
return affectedEntitiesCount

But I have no idea how to modify book according requirements.
Can someone take a look and suggest?

Tags:

2

Answers


  1. Chosen as BEST ANSWER
    0

    solved:

    local book
local cacheName
local authorPattern= '"author":"[^"]*"'
local authorId
local replacementAuthors = '"authors":["java.util.ArrayList",["%s"]]'

local size = redis.call('LLEN', cacheName)
if size == 0
then
    return -1
end

while size > 0
do
    book = redis.call('LPOP', cacheName)
    
    authorId = string.match(string.match(book, authorPattern), [["authorId":"([^"]+)]])
    replacedAuthors = string.format(replacedAuthors , authorId)
    book = string.gsub(book, authorPattern, replacedAuthors)
    
    affectedEntitiesCount = affectedEntitiesCount + 1
    redis.call('RPUSH', cacheName, book)
    size = size - 1
end
return affectedEntitiesCount

  2. 0

    Since it appears that you’re storing JSON-encoded values in your list, you can use the cjson library that’s embedded in Redis’ Lua engine.

    For example:

        ...
    book = cjson.decode(redis.call('LPOP', cacheName))
    book['bookId'] = book['bookId']..'foo' -- concat 'foo' to bookId
    ...
    redis.call('RPUSH', cacheName, cjson.encode(book))

    Note: also make sure that you use the KEYS input array to parameterize the script’s input key names (e.g. local cacheName = KEYS[1])

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