We can use partial word matching to rapidly search strings of text such as Names, Cities, States, etc.
We can do this by indexing strings into Redis sets based on partial matches of the string. The indexing process takes a string and breaks it into left-bound substrings which are placed into the appropriate Redis sets.
Partial word matching movie titles
In this example we’ll enable partial word matching queries of movie titles.
The movie titles will be stored in plain text. The keys are simple key-value
pairs that are stored with the key structure movies:id, where id is
incremented:
$ redis-cli get movies:1
"Bad Santa"
$ redis-cli get movies:2
"Batman"
$ redis-cli get movies:3
"Bad Company"
The movie Batman would be decomposed into the following sets (assuming that
the indexing started at two characters):
ba
bat
batm
batma
batman
We’ll index the movie titles into sets based on partial match of their titles.
To prevent any key collisions in Redis we’ll create keys with the following
structue index:abc:movies.
View the indexed ids using Redis smembers command:
$ redis-cli smembers index:ba:movies
1) "1"
2) "2"
3) "3"
$ redis-cli smembers index:bat:movies
1) "2"
Note: The keys for the movie titles have been parameterized (lowercase and spaces replaced with dashes).
We’ll use a Ruby class Autocomplete to wrap the Redis calls:
# autocomplete.rb
require 'redis'
class Autocomplete
def initialize(partial_word)
@partial_word = partial_word
end
def movies
redis.sort "index:#{partial_word}:movies", by: :nosort, get: 'movies:*'
end
private
def redis
Redis.current
end
attr_reader :partial_word
end
movies = Autocomplete.new('bat').movies
We’ll use the sort command with the by: :nosort parameter to query the
partial word match index and return the matched movie names.
