LUA script for modification object in Redis - redis

Question

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?

Answer 1

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

Answer 2

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])